AFE4403 [TI]
AFE4403 Ultra-Small, Integrated Analog Front-End for Heart Rate Monitors and Low-Cost Pulse Oximeters;型号: | AFE4403 |
厂家: | TEXAS INSTRUMENTS |
描述: | AFE4403 Ultra-Small, Integrated Analog Front-End for Heart Rate Monitors and Low-Cost Pulse Oximeters |
文件: | 总97页 (文件大小:1840K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
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AFE4403
SBAS650B –MAY 2014–REVISED JULY 2014
AFE4403 Ultra-Small, Integrated Analog Front-End for Heart Rate Monitors and
Low-Cost Pulse Oximeters
1 Features
2 Applications
1
•
Fully-Integrated AFE for Pulse Oximeter and
Heart Rate Monitoring Applications:
•
•
•
Medical Pulse Oximeter Applications
Optical HRM
•
Transmit:
Industrial Photometry Applications
–
Integrated Dual LED Driver
3 Description
(H-Bridge or Common Anode)
The AFE4403 is a fully-integrated analog front-end
(AFE) ideally suited for pulse oximeter applications.
The device consists of a low-noise receiver channel
with an integrated analog-to-digital converter (ADC),
an LED transmit section, and diagnostics for sensor
and LED fault detection. The device is a very
configurable timing controller. This flexibility enables
the user to have complete control of the device timing
characteristics. To ease clocking requirements and
provide a low-jitter clock to the AFE4403, an oscillator
is also integrated that functions from an external
crystal. The device communicates to an external
microcontroller or host processor using an SPI™
interface.
–
Option for a Third LED Support for Optimized
SPO2, HRM, or Multi-Wavelength HRM
–
–
Up to 110-dB Dynamic Range
LED Current:
–
Programmable to 100 mA with 8-Bit
Current Resolution
–
–
–
30 µA + Average LED Current
Programmable LED On-Time
Independent LED2 and LED1 Current
Reference
•
Receive Channel with High Dynamic Range:
–
–
–
–
22-Bit Output in Twos Complement Format
Up to 105-dB Dynamic Range
Low Power: < 650 µA
The device is a complete AFE solution packaged in a
single, compact DSBGA-36 (3.07 mm × 3.07 mm ×
0.5 mm) and is specified over the operating
temperature range of –20°C to 70°C.
Dynamic Power-Down Mode to Reduce
Current to 300 µA
Device Information(1)
–
–
Adaptable to a Very Wide Range of Signal
Amplitudes:
PART NUMBER
PACKAGE
BODY SIZE (NOM)
AFE4403
DSBGA (36)
3.07 mm × 3.07 mm
–
Total Programmable Gain: 10 kΩ to 4 MΩ
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Integrated Digital Ambient Estimation and
Subtraction
•
Flexible Clocking by External Clock or Crystal:
–
–
–
Pulse Frequency: 62.5 SPS to 2000 SPS
Flexible Pulse sequencing and Timing Control
Input Clock Range: 4 MHz (Min) to 60 MHz
(Max)
•
•
Integrated Fault Diagnostics:
–
Photodiode and LED Open and
Short Detection
Supplies:
–
–
Rx = 2.0 V to 3.6 V
Tx = 3.0 V to 5.25 V
•
•
Package: Compact DSBGA-36
(3.07 mm × 3.07 mm × 0.5 mm)
Specified Temperature Range: –20°C to 70°C
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
AFE4403
SBAS650B –MAY 2014–REVISED JULY 2014
www.ti.com
Table of Contents
8.2 Functional Block Diagram ....................................... 20
8.3 Feature Description................................................. 21
8.4 Device Functional Modes........................................ 45
8.5 Programming........................................................... 53
8.6 Register Maps......................................................... 58
Application and Implementation ........................ 83
9.1 Application Information............................................ 83
9.2 Typical Application .................................................. 83
1
2
3
4
5
6
7
Features.................................................................. 1
Applications ........................................................... 1
Description ............................................................. 1
Revision History..................................................... 2
Device Family Options .......................................... 3
Pin Configuration and Functions......................... 3
Specifications......................................................... 5
7.1 Absolute Maximum Ratings ...................................... 5
7.2 Handling Ratings....................................................... 5
7.3 Recommended Operating Conditions....................... 6
7.4 Thermal Information.................................................. 6
7.5 Electrical Characteristics........................................... 7
7.6 Timing Requirements.............................................. 11
9
10 Power Supply Recommendations ..................... 87
10.1 Power Consumption Considerations..................... 88
11 Layout................................................................... 90
11.1 Layout Guidelines ................................................. 90
11.2 Layout Example .................................................... 90
12 Device and Documentation Support ................. 91
12.1 Trademarks........................................................... 91
12.2 Electrostatic Discharge Caution............................ 91
12.3 Glossary................................................................ 91
7.7 Timing Requirements: Supply Ramp and Power-
Down........................................................................ 12
7.8 Typical Characteristics............................................ 14
Detailed Description ............................................ 20
8.1 Overview ................................................................. 20
8
13 Mechanical, Packaging, and Orderable
Information ........................................................... 91
4 Revision History
Changes from Revision A (June 2014) to Revision B
Page
•
•
Changed Pin Configuration diagram: changed Top View to Bottom View ............................................................................ 3
Added footnote to Figure 41 ................................................................................................................................................ 27
Changes from Original (May 2014) to Revision A
Page
•
•
•
•
•
•
•
•
•
Changed document status to Production Data ...................................................................................................................... 1
Changed first and third sub-bullets of Flexible Clocking Features bullet .............................................................................. 1
Changed MIN to NOM in Body Size column of Device Information table ............................................................................. 1
Added Device Family Options table and Pin Configuration and Functions section ............................................................... 3
Added Specifications section ................................................................................................................................................. 5
Added Detailed Description section ..................................................................................................................................... 20
Added Application and Implementation section.................................................................................................................... 83
Added Power Supply Recommendations section ............................................................................................................... 87
Added Layout section .......................................................................................................................................................... 90
2
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SBAS650B –MAY 2014–REVISED JULY 2014
5 Device Family Options
LED DRIVE
CURRENT
(mA, max)
OPERATING
TEMPERATURE
RANGE
LED DRIVE
CONFIGURATION
Tx POWER SUPPLY
(V)
PRODUCT
PACKAGE-LEAD
AFE4400
VQFN-40
Bridge, push-pull
Bridge, push-pull
Bridge, push-pull
50
3 to 5.25
3 to 5.25
3 to 5.25
0°C to 70°C
–40°C to 85°C
–20°C to 70°C
50, 75, 100,
150, and 200
AFE4490
AFE4403
VQFN-40
DSBGA-36
25, 50, 75, and 100
6 Pin Configuration and Functions
YZP Package
DSBGA-36
(Bottom View)
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Pin Functions
PIN
NAME
NO.
FUNCTION
DESCRIPTION
Output signal that indicates ADC conversion completion.
Can be connected to the interrupt input pin of an external microcontroller.
ADC_RDY
D5
Digital
AFE-only power-down input; active low.
Can be connected to the port pin of an external microcontroller.
AFE_PDN
BG
C3
C2
Digital
Decoupling capacitor for internal band-gap voltage to ground.
Connect a decoupling capacitor to ground.
To achieve the lowest transmitter noise, use a capacitor value of 2.2 µF.
Reference
To reduce the recovery time from power-down (from 1 s to 0.1 s), use a capacitor value of
0.1 µF instead—but with slightly degraded transmitter noise.
Buffered 4-MHz output clock output.
Can be connected to the clock input pin of an external microcontroller.
CLKOUT
DIAG_END
DNC(1)
E6
B4
Digital
Digital
—
Output signal that indicates completion of diagnostics.
Can be connected to the port pin of an external microcontroller.
C1, A1, E3, D3,
F5, B5, B6
Do not connect these pins. Leave as open circuit.
INN
INP
F1
E1
A3
Analog
Analog
Supply
Receiver input pin. Connect to photodiode anode.
Receiver input pin. Connect to photodiode cathode.
LED driver ground pin, H-bridge. Connect to common board ground.
LED_DRV_GND
LED driver supply pin, H-bridge. Connect to an external power supply capable of supplying the
large LED current, which is drawn by this supply pin.
LED_DRV_SUP
RESET
A6
D4
Supply
Digital
AFE-only reset input, active low.
Can be connected to the port pin of an external microcontroller
RX_ANA_GND
RX_ANA_SUP
RX_DIG_GND
RX_DIG_SUP
SCLK
E2
F2, E4
B2, F6
E5
Supply
Supply
Supply
Supply
SPI
Rx analog ground pin. Connect to common board ground.
Rx analog supply pin; 0.1-µF decoupling capacitor to ground
Rx digital ground pin. Connect to common board ground.
Rx digital supply pin; 0.1-µF decoupling capacitor to ground
SPI clock pin
C6
SPISIMO
C4
SPI
SPI serial in master out
SPISOMI
C5
SPI
SPI serial out master in
SPISTE
D6
SPI
SPI serial interface enable
TX_CTRL_SUP
A2
Supply
Transmit control supply pin (0.1-µF decoupling capacitor to ground)
Transmitter reference voltage, 0.25 V default after reset.
Connect a decoupling capacitor to ground.
TX_REF
B1
Reference
To achieve the lowest transmitter noise, use a capacitor value of 2.2 µF.
To reduce the recovery time from power-down (from 1 s to 0.1 s), use a capacitor value of
0.1 µF instead—but with slightly degraded transmitter noise.
TXN
TXP
A4
A5
Analog
Analog
LED driver out. Connect to LED in common anode or H-bridge configuration.
LED driver out. Connect to LED in common anode or H-bridge configuration.
LED driver out for third LED. Connect to optional third LED supported in common anode
configuration.
TX3
B3
Analog
Input common-mode voltage output.
This signal can be used to shield (guard) the INP, INN traces.
If used as a shield, then connect a series resistor (1 kΩ) and a decoupling capacitor (10 nF) to
ground.
VCM
D1
Reference
If VCM is not used externally, then these external components are not required.
VSS
D2
F4
Supply
Digital
Substrate ground. Connect to common board ground.
Crystal oscillator pins.
Connect an external crystal between these pins with the correct load capacitor
(as specified by vendor) to ground.
XOUT
Crystal oscillator pins.
XIN
F3
Digital
Connect an external crystal between these pins with the correct load capacitor
(as specified by vendor) to ground.
(1) Leave pins as open circuit. Do not connect.
4
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SBAS650B –MAY 2014–REVISED JULY 2014
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)
MIN
–0.3
–0.3
–0.3
MAX
UNIT
V
RX_ANA_SUP, RX_DIG_SUP to RX_ANA_GND, RX_DIG_GND
TX_CTRL_SUP, LED_DRV_SUP to LED_DRV_GND
RX_ANA_GND, RX_DIG_GND to LED_DRV_GND
4
6
V
0.3
V
Analog inputs
RX_ANA_GND – 0.3
RX_DIG_GND – 0.3
RX_ANA_SUP + 0.3
V
Digital inputs
RX_DIG_SUP + 0.3
V
Input current to any pin except supply pins(2)
±7
±50
±7
mA
mA
mA
°C
°C
Momentary
Input current
Continuous
Operating temperature range
0–20
70
Maximum junction temperature, TJ
125
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) Input terminals are diode-clamped to the power-supply rails. Input signals that can swing beyond the supply rails must be current-limited
to 10 mA or less.
7.2 Handling Ratings
MIN
MAX
UNIT
Tstg
Storage temperature range
–60
150
°C
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all
pins(1)
–1000
–250
1000
250
V(ESD)
Electrostatic discharge
V
Charged device model (CDM), per JEDEC specification
JESD22-C101, all pins(2)
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
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7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
PARAMETER
SUPPLIES
MIN
MAX
UNIT
RX_ANA_SUP
RX_DIG_SUP
TX_CTRL_SUP
AFE analog supply
2.0
2.0
3.0
3.6
3.6
V
V
V
AFE digital supply
Transmit controller supply
5.25
(1)(2)
[3.0 or (0.75 + VLED + VCABLE
)
,
H-bridge
5.25
5.25
0.3
V
V
V
whichever is greater]
LED_DRV_SUP
Transmit LED driver supply
(1)(2)
Common anode
configuration
[3.0 or (0.5 + VLED + VCABLE
)
,
whichever is greater]
Difference between LED_DRV_SUP and
TX_CTRL_SUP
–0.3
TEMPERATURE
Specified temperature range
Storage temperature range
–20
–60
70
°C
°C
150
(1) VLED refers to the maximum voltage drop across the external LED (at maximum LED current) connected between the TXP and TXN pins
(in H-bridge mode) and from the TXP and TXN pins to LED_DRV_SUP (in the common anode configuration).
(2) VCABLE refers to voltage drop across any cable, connector, or any other component in series with the LED.
7.4 Thermal Information
AFE4403
THERMAL METRIC(1)
YZP (WCSP)
UNIT
36 BALLS
49.8
0.2
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
RθJB
Junction-to-case (top) thermal resistance
Junction-to-board thermal resistance
8.5
°C/W
ψJT
Junction-to-top characterization parameter
Junction-to-board characterization parameter
Junction-to-case (bottom) thermal resistance
0.8
ψJB
8.5
RθJC(bot)
n/a
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
6
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SBAS650B –MAY 2014–REVISED JULY 2014
7.5 Electrical Characteristics
Minimum and maximum specifications are at TA = –20°C to 70°C, typical specifications are at 25°C. Crystal mode enabled,
detector capacitor = 50 pF differential, ADC averaging set to maximum allowed for each PRF, TX_REF voltage set to 0.5 V,
and CLKOUT tri-stated, at RX_ANA_SUP = RX_DIG_SUP = 3 V, TX_CTRL_SUP = LED_DRV_SUP = 3.3 V, stage 2
amplifier disabled, and fCLK = 8 MHz, unless otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
PERFORMANCE (Full-Signal Chain)
RF = 10 kΩ
RF = 25 kΩ
RF = 50 kΩ
RF = 100 kΩ
RF = 250 kΩ
RF = 500 kΩ
RF = 1 MΩ
50
20
10
5
µA
µA
µA
IIN_FS
Full-scale input current
µA
2
µA
1
µA
0.5
µA
PRF
Pulse repetition frequency
PRF duty cycle
62.5
2000
25%
SPS
DCPRF
fCM = 50 Hz and 60 Hz, LED1 and LED2 with
RSERIES = 500 kΩ, RF = 500 kΩ
75
95
dB
dB
CMRR
Common-mode rejection ratio
fCM = 50 Hz and 60 Hz, LED1-AMB and LED2-AMB with
RSERIES = 500 kΩ, RF = 500 kΩ
PSRRLED PSRR, transmit LED driver
PSRRTx PSRR, transmit control
PSRRRx PSRR, receiver
Total integrated noise current, input-
With respect to ripple on LED_DRV_SUP
75
60
60
25
dB
dB
With respect to ripple on TX_CTRL_SUP
With respect to ripple on RX_ANA_SUP and RX_DIG_SUP
RF = 100 kΩ, PRF = 600 Hz, duty cycle = 5%
dB
pARMS
referred (receiver with transmitter loop
back, 0.1-Hz to 20-Hz bandwidth)
RF = 500 kΩ, PRF = 600 Hz, duty cycle = 5%
6
pARMS
RECEIVER FUNCTIONAL BLOCK LEVEL SPECIFICATION
RF = 500 kΩ, ambient cancellation enabled,
stage 2 gain = 4, PRF = 1200 Hz, LED duty cycle = 25%
3.2
5.3
pARMS
pARMS
Total integrated noise current, input
referred (receiver alone) over 0.1-Hz to
20-Hz bandwidth
RF = 500 kΩ, ambient cancellation enabled,
stage 2 gain = 4, PRF = 1200 Hz, LED duty cycle = 5%
I-V TRANSIMPEDANCE AMPLIFIER
See the Receiver Channel
G
Gain
RF = 10 kΩ to 1 MΩ
V/µA
section for details
Gain accuracy
Feedback resistance
±7%
10k, 25k, 50k, 100k, 250k,
500k, and 1M
RF
Ω
Feedback resistor tolerance
Feedback capacitance
RF
CF
CF
±20%
5, 10, 25, 50, 100, and 250
pF
Feedback capacitor tolerance
Full-scale differential output voltage
Common-mode voltage on input pins
±20%
1
V
V
Set internally
0.9
Includes equivalent capacitance of photodiode, cables,
EMI filter, and so forth
External differential input capacitance
Shield output voltage, VCM
10
1000
pF
V
With a 1-kΩ series resistor and a 10-nF decoupling
capacitor to ground
0.8
0.9
1
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Electrical Characteristics (continued)
Minimum and maximum specifications are at TA = –20°C to 70°C, typical specifications are at 25°C. Crystal mode enabled,
detector capacitor = 50 pF differential, ADC averaging set to maximum allowed for each PRF, TX_REF voltage set to 0.5 V,
and CLKOUT tri-stated, at RX_ANA_SUP = RX_DIG_SUP = 3 V, TX_CTRL_SUP = LED_DRV_SUP = 3.3 V, stage 2
amplifier disabled, and fCLK = 8 MHz, unless otherwise noted.
PARAMETER
AMBIENT CANCELLATION STAGE
Gain
TEST CONDITIONS
MIN
TYP
MAX
UNIT
0, 3.5, 6, 9.5, and 12
dB
µA
µA
Current DAC range
0
10
Current DAC step size
LOW-PASS FILTER
1
Low-pass corner frequency
3-dB attenuation
Duty cycle = 25%
Duty cycle = 10%
500
0.004
0.041
28
Hz
dB
dB
ms
Pass-band attenuation, 2 Hz to 10 Hz
Filter settling time
ANALOG-TO-DIGITAL CONVERTER
Resolution
After diagnostics mode
22
Bits
SPS
V
Sample rate
See the ADC Operation and Averaging Module section
See the ADC Operation and Averaging Module section
4 × PRF
±1.2
ADC full-scale voltage
ADC conversion time
ADC reset time(1)
PRF / 4
µs
2
tCLK
TRANSMITTER
Selectable, 0 to 100
(see the LEDCNTRL: LED
Control Register for details)
Output current range
mA
LED current DAC error
Output current resolution
±10%
8
Bits
dB
Transmitter noise dynamic range,
over 0.1-Hz to 20-Hz bandwidth,
TX_REF set to 0.5 V
At 25-mA output current
At 50-mA output current
110
110
50
dB
µs
Minimum sample time of LED1 and
LED2 pulses
LED_ON = 0
1
50
0.50
7
µA
µA
%
LED current DAC leakage current
LED current DAC linearity
LED_ON = 1
Percent of full-scale current
From zero current to 50 mA
From 50 mA to zero current
µs
µs
Output current settling time
(with resistive load)
7
DIAGNOSTICS
Start of diagnostics after the DIAG_EN register bit is set.
End of diagnostic is indicated by DIAG_END going high.
Duration of diagnostics state machine
16
ms
Open fault resistance
Short fault resistance
> 100
< 10
kΩ
kΩ
INTERNAL OSCILLATOR
fCLKOUT
CLKOUT frequency
With an 8-MHz crystal connected to the XIN, XOUT pins
With an 8-MHz crystal connected to the XIN, XOUT pins
4
50%
200
MHz
CLKOUT duty cycle
Crystal oscillator start-up time
µs
(1) A low ADC reset time can result in a small component of the LED signal leaking into the ambient phase. With an ADC reset of two clock
cycles, a –60-dB leakage is expected. In many cases, this leakage does not affect system performance. However, if this crosstalk must
be completely eliminated, a longer ADC reset time of approximately six clock cycles is recommended for t22, t24, t26, and t28 in
Figure 48.
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Electrical Characteristics (continued)
Minimum and maximum specifications are at TA = –20°C to 70°C, typical specifications are at 25°C. Crystal mode enabled,
detector capacitor = 50 pF differential, ADC averaging set to maximum allowed for each PRF, TX_REF voltage set to 0.5 V,
and CLKOUT tri-stated, at RX_ANA_SUP = RX_DIG_SUP = 3 V, TX_CTRL_SUP = LED_DRV_SUP = 3.3 V, stage 2
amplifier disabled, and fCLK = 8 MHz, unless otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
EXTERNAL CLOCK
For SPO2 applications
50
ps
ps
Maximum allowable external clock jitter
For optical heart rate only
±2%
1000
60
(2)
External clock input frequency
4
8
MHz
0.75 ×
RX_DIG_SUP
Voltage input high (VIH
)
V
V
External clock input voltage
0.25 ×
RX_DIG_SUP
Voltage input low (VIL)
TIMING
Wake-up time from complete
power-down
1000
ms
Wake-up time from Rx power-down
Wake-up time from Tx power-down
Active low RESET pulse duration
100
1000
1
µs
ms
ms
tRESET
DIAG_END pulse duration at the
completion of diagnostics
CLKOUT
cycles
tDIAGEND
4
1
CLKOUT
cycle
tADCRDY
ADC_RDY pulse duration
DIGITAL SIGNAL CHARACTERISTICS
0.8
DVDD
DVDD +
0.1
VIH
Logic high input voltage
AFE_PDN, SCLK, SPISIMO, SPISTE, RESET
> 1.3
V
0.2
DVDD
VIL
IIN
Logic low input voltage
Logic input current
AFE_PDN, SCLK, SPISIMO, SPISTE, RESET
0 V < VDigitalInput < DVDD
–0.1
–10
< 0.4
V
µA
V
10
0.9
DVDD
> (RX_DIG_SUP –
0.2 V)
VOH
Logic high output voltage
DIAG_END, SPISOMI, ADC_RDY, CLKOUT
0.1
< 0.4
VOL
Logic low output voltage
DIAG_END, SPISOMI, ADC_RDY, CLKOUT
V
DVDD
SUPPLY CURRENT
RX_ANA_SUP = 3.0 V, with 8-MHz clock running,
Rx stage 2 disabled
0.6
0.7
mA
mA
mA
RX_ANA_SUP = 3.0 V, with 8-MHz clock running,
Rx stage 2 enabled
Receiver analog supply current
RX_ANA_SUP = 3.0 V, with 8-MHz clock running,
Rx stage 2 disabled, external clock mode
0.49
Receiver digital supply current
LED driver supply current
RX_DIG_SUP = 3.0 V
0.15
30
15
3
mA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
With zero LED current setting
Transmitter control supply current
Receiver current only (RX_ANA_SUP)
Receiver current only (RX_DIG_SUP)
Transmitter current only (LED_DRV_SUP)
Transmitter current only (TX_CTRL_SUP)
Receiver current only (RX_ANA_SUP)
Receiver current only (RX_DIG_SUP)
Transmitter current only (LED_DRV_SUP)
Transmitter current only (TX_CTRL_SUP)
3
Complete power-down
(using the AFE_PDN pin)
1
1
200
150
2
Power-down Rx alone
Power-down Tx alone
2
(2) Refer to the CLKDIV[2:0] register bits for a detailed list of input clock frequencies that are supported.
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Electrical Characteristics (continued)
Minimum and maximum specifications are at TA = –20°C to 70°C, typical specifications are at 25°C. Crystal mode enabled,
detector capacitor = 50 pF differential, ADC averaging set to maximum allowed for each PRF, TX_REF voltage set to 0.5 V,
and CLKOUT tri-stated, at RX_ANA_SUP = RX_DIG_SUP = 3 V, TX_CTRL_SUP = LED_DRV_SUP = 3.3 V, stage 2
amplifier disabled, and fCLK = 8 MHz, unless otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
POWER DISSIPATION
LED_DRV_SUP Does not include LED current.
1
1
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
TX_CTRL_SUP
Power-down with
the AFE_PDN pin
RX_ANA_SUP
5
RX_DIG_SUP
0.1
1
LED_DRV_SUP Does not include LED current.
TX_CTRL_SUP
Power-down with
the PDNAFE
register bit
1
RX_ANA_SUP
15
20
30
15
200
150
2
RX_DIG_SUP
LED_DRV_SUP Does not include LED current.
TX_CTRL_SUP
Power-down Rx
Power-down Tx
RX_ANA_SUP
RX_DIG_SUP
LED_DRV_SUP Does not include LED current.
TX_CTRL_SUP
2
RX_ANA_SUP
600
150
30
15
600
150
30
15
700
150
RX_DIG_SUP
LED_DRV_SUP Does not include LED current.
TX_CTRL_SUP
After reset, with 8-
MHz clock running
RX_ANA_SUP
RX_DIG_SUP
LED_DRV_SUP Does not include LED current.
TX_CTRL_SUP
With stage 2 mode
enabled and 8-MHz
clock running
RX_ANA_SUP
RX_DIG_SUP
Does not include LED
LED_DRV_SUP
current.
7
µA
Dynamic power-
down mode enabled
PRF = 100 Hz,
PDN_CYCLE duration = 8 ms
TX_CTRL_SUP
RX_ANA_SUP
RX_DIG_SUP
5
205
150
µA
µA
µA
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7.6 Timing Requirements
PARAMETER
MIN
TYP
MAX
UNIT
MHz
ns
tCLK
Clock frequency on the XIN pin
8
tSCLK
Serial shift clock period
62.5
10
tSTECLK
tCLKSTEH,L
tSIMOSU
tSIMOHD
tSOMIPD
tSOMIHD
STE low to SCLK rising edge, setup time
SCLK transition to SPI STE high or low
SIMO data to SCLK rising edge, setup time
Valid SIMO data after SCLK rising edge, hold time
SCLK falling edge to valid SOMI, setup time
SCLK rising edge to invalid data, hold time
ns
10
ns
10
ns
10
ns
17
ns
0.5
tSCLK
tCLK
XIN
tSTECLK
SPISTE
tSPICLK
tCLKSTEH
31
23
7
0
SCLK
tCLKSTEL
tSIMOHD
tSIMOSU
A7
A6
A1
A0
SPISIMO
SPISOMI
tSOMIHD
tSOMIPD
tSOMIPD
D22
D17 D16
D23
D7
D6
D1
D0
ꢀ}v[ꢁꢀꢁꢂ, can be high or low.
(1) The SPI_READ register bit must be enabled before attempting a register read.
(2) Specify the register address whose contents must be read back on A[7:0].
(3) The AFE outputs the contents of the specified register on the SPISOMI pin.
Figure 1. Serial Interface Timing Diagram, Read Operation(1)(2)(3)
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tSTECLK
SPISTE
31
23
0
SCLK
tSIMOHD
tSIMOSU
A7
A6
A1
A0
D23
D22
D1
D0
SPISIMO
Figure 2. Serial Interface Timing Diagram, Write Operation
7.7 Timing Requirements: Supply Ramp and Power-Down
PARAMETER
VALUE
t1
t2
t3
t4
Time between Rx and Tx supplies ramping up
Time between both supplies stabilizing and high-going RESET edge
RESET pulse duration
Keep as small as possible (for example, ±10 ms)
> 100 ms
> 0.5 ms
> 1 µs
Time between RESET and SPI commands
Time between SPI commands and the ADC_RESET which corresponds > 3 ms of cumulative sampling time in each
to valid data
t5
phase(1)(2)(3)
> 1 s(3)
Time between RESET pulse and high-accuracy data coming out of the
signal chain
t6
t7
t8
Time from AFE_PDN high-going edge and RESET pulse(4)
> 100 ms
> 1 s(3)
Time from AFE_PDN high-going edge (or PDN_AFE bit reset) to high-
accuracy data coming out of the signal chain
(1) This time is required for each of the four switched RC filters to fully settle to the new settings. The same time is applicable whenever
there is a change to any of the signal chain controls (for example, LED current setting, TIA gain, and so forth).
(2) If the SPI commands involve a change in the TX_REF value from its default, then there is additional wait time of approximately 1 s (for a
2.2-µF decoupling capacitor on the TX_REF pin).
(3) Dependent on the value of the capacitors on the BG and TX_REF pins. The 1-s wait time is necessary when the capacitors are 2.2 µF
and scale down proportionate to the capacitor value. A very low capacitor (for example, 0.1 µF) on these pins causes the transmitter
dynamic range to reduce to approximately 100 dB.
(4) After an active power-down from AFE_PDN, the device should be reset using a low-going RESET pulse.
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RX Supplies
(RX_ANA_SUP, RX_DIG_SUP)
t1
TX Supplies
(TX_CTRL_SUP, LED_DRV_SUP)
t2
t6
RESET
t3
t4
t4
t5
t5
SPI Interface
t7
t3
ADC_RDY
AFE_PDN
t6
t8
Figure 3. Supply Ramp and Hardware Power-Down Timing
RX Supplies
(RX_ANA_SUP, RX_DIG_SUP)
t1
TX Supplies
(TX_CTRL_SUP, LED_DRV_SUP)
t2
PDN_AFE
Bit Set
PDN_AFE Bit
Reset
RESET
t8
t3
t4
t5
SPI Interface
ADC_RDY
AFE_PDN
t6
Figure 4. Supply Ramp and Software Power-Down Timing
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7.8 Typical Characteristics
At PRF = 100 Hz, 25% duty cycle, RF = 500 kΩ, CF is adjusted to keep TIA time constant at 1/10th of sampling duration, All
supplies at 3.3 V, 8-MHz external clock, CLKOUT tri-state, 1-µF capacitor on TX_REF and BG pins, detector CIN = 50 pF,
TX_REF = 0.5 V, ADC averaging = max allowed, and SNR in dBFS is noise referred to full-scale range of 2 V, unless
otherwise noted.
600
500
400
300
200
100
50
40
30
20
10
0
I(LED_DRV_SUP)
I(TX_CTRL_SUP)
I(RX_DIG_SUP)
I(RX_ANA_SUP)
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
2.6
3
3.4
3.8
4.2
4.6
5
Receiver Supply Voltage (V)
Transmitter Supply Voltage (V)
C001
C002
LED current = 0 mA
Figure 5. Receiver Currents vs Receiver Supply Voltage
Figure 6. Transmitter Currents vs
Transmitter Supply Voltage
1200
1000
800
700
600
500
400
300
200
Clock Division Ratio = 1
Clock Division Ratio = 2
Clock Division Ratio = 4
Clock Division Ratio = 6
Clock Division Ratio = 8
Clock Division Ratio = 12
600
400
200
0
10
20
30
40
50
60
50
250
450
650
850
1050
1250
External Clock Frequency (MHz)
PRF (Hz)
C003
C004
PRF = 150 Hz
Active window = 500 µs
LED pulse = 100 µs
All four DYNAMIC bits set to 1
Figure 7. Receiver Currents (Analog and Digital) vs
Clock Divider Ratio
Figure 8. Receiver Current vs
PRF in Dynamic Power-Down Mode
700
600
500
400
300
200
5
±5
±15
±25
±35
±45
5% Duty cycle
25% Duty cycle
0
1
2
3
4
5
6
7
8
9
1
10
100
1000
PDN_CYCLE Width (ms)
Frequency (Hz) in Log Scale
C005
C030
PRF = 100 Hz
LED pulse = 100 µs
All four DYNAMIC bits set to 1
Figure 9. Receiver Current (Analog and Digital) vs
Dynamic Power-Down Duty Cycle
Figure 10. Filter Response vs Duty cycle
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Typical Characteristics (continued)
At PRF = 100 Hz, 25% duty cycle, RF = 500 kΩ, CF is adjusted to keep TIA time constant at 1/10th of sampling duration, All
supplies at 3.3 V, 8-MHz external clock, CLKOUT tri-state, 1-µF capacitor on TX_REF and BG pins, detector CIN = 50 pF,
TX_REF = 0.5 V, ADC averaging = max allowed, and SNR in dBFS is noise referred to full-scale range of 2 V, unless
otherwise noted.
106
104
102
100
98
50
45
40
35
30
25
20
15
10
Output voltage = 0 %FS
Output voltage = 10 %FS
Output voltage = 25 %FS
Output voltage = 50 %FS
Output voltage = 75 %FS
Output voltage = 0 %FS
Output voltage = 10 %FS
Output voltage = 25 %FS
Output voltage = 50 %FS
Output voltage = 75 %FS
96
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C007
C006
500-Hz PRF
500-Hz PRF
Figure 11. SNR over Nyquist Bandwidth vs Duty Cycle
(Input Current with Tx-Rx Loopback)
Figure 12. Input-Referred Noise Current over Nyquist
Bandwidth vs Duty Cycle
(Input Current with Tx-Rx Loopback)
100000
108
RF = 10 kꢀ
RF = 10 kꢀ
RF = 25 kꢀ
RF = 50 kꢀ
RF = 25 kꢀ
10000
1000
100
10
RF = 100 kꢀ
RF = 250 kꢀ
RF = 500 kꢀ
RF = 1000 kꢀ
106
RF = 50 kꢀ
RF = 100 kꢀ
RF = 250 kꢀ
RF = 500 kꢀ
RF = 1000 kꢀ
104
102
100
98
1
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C011
C008
Figure 14. Receiver Input-Referred Noise Current over
Nyquist Bandwidth vs Duty Cycle (Different Gain Settings)
Figure 13. Receiver SNR over Nyquist Bandwidth vs
Duty Cycle (Different Gain Settings)
112
100000
RF = 10 kꢀ
RF = 25 kꢀ
RF = 50 kꢀ
RF = 100 kꢀ
RF = 250 kꢀ
RF = 500 kꢀ
RF = 1000 kꢀ
RF = 10 kꢀ
RF = 25 kꢀ
RF = 50 kꢀ
110
108
106
104
102
10000
RF = 100 kꢀ
RF = 250 kꢀ
RF = 500 kꢀ
RF = 1000 kꢀ
1000
100
10
1
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C009
C010
Figure 15. Receiver SNR in 20-Hz BW vs Duty Cycle
(Different Gain Settings)
Figure 16. Receiver Input-Referred Noise Current in
20-Hz BW vs Duty Cycle (Different Gain Settings)
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Typical Characteristics (continued)
At PRF = 100 Hz, 25% duty cycle, RF = 500 kΩ, CF is adjusted to keep TIA time constant at 1/10th of sampling duration, All
supplies at 3.3 V, 8-MHz external clock, CLKOUT tri-state, 1-µF capacitor on TX_REF and BG pins, detector CIN = 50 pF,
TX_REF = 0.5 V, ADC averaging = max allowed, and SNR in dBFS is noise referred to full-scale range of 2 V, unless
otherwise noted.
102
40
30
20
10
0
98
94
ADC Averaging = 1
ADC Averaging = 2
ADC Averaging = 4
ADC Averaging = 8
ADC Averaging = 16
ADC Averaging = 1
ADC Averaging = 2
ADC Averaging = 4
ADC Averaging = 8
ADC Averaging = 16
90
86
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C013
C012
Figure 17. Receiver SNR over Nyquist Bandwidth vs
Duty Cycle (Different ADC Averaging)
Figure 18. Receiver Input-Referred Noise Current over
Nyquist Bandwidth vs Duty Cycle (Different ADC Averaging)
116
112
108
104
30
PRF = 62.5 Hz
PRF = 100 Hz
PRF = 500 Hz
PRF = 1000 Hz
25
20
PRF = 2000 Hz
15
10
5
PRF = 62.5 Hz
PRF = 100 Hz
PRF = 500 Hz
100
96
PRF = 1000 Hz
PRF = 2000 Hz
92
0
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C015
C014
Figure 19. Receiver SNR in 20-Hz BW vs Duty Cycle
(Different PRFs)
Figure 20. Receiver Input Referred Noise in 20-Hz BW vs
Duty Cycle (Different PRFs)
112
108
104
100
96
25
20
15
10
5
0
0
250
500
750
1000
1250
0
250
500
750
1000
1250
PRF (Hz)
PRF (Hz)
C017
C016
Active window = 500 µs
LED pulse = 100 µs
All four DYNAMIC bits set to 1
Active window = 500 µs
LED pulse = 100 µs
All four DYNAMIC bits set to 1
Figure 21. Receiver SNR in 20-Hz BW in Dynamic
Power-Down Mode vs PRF
Figure 22. Receiver Input-Referred Noise in 20-Hz BW in
Dynamic Power-Down Mode vs PRF
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Typical Characteristics (continued)
At PRF = 100 Hz, 25% duty cycle, RF = 500 kΩ, CF is adjusted to keep TIA time constant at 1/10th of sampling duration, All
supplies at 3.3 V, 8-MHz external clock, CLKOUT tri-state, 1-µF capacitor on TX_REF and BG pins, detector CIN = 50 pF,
TX_REF = 0.5 V, ADC averaging = max allowed, and SNR in dBFS is noise referred to full-scale range of 2 V, unless
otherwise noted.
106
104
102
100
98
30
26
22
18
14
10
96
0
2
4
6
8
10
0
2
4
6
8
10
Dynamic Powerdown Cycle Width (ms)
Dynamic Powerdown Cycle width (ms)
C019
C018
PRF = 100 Hz
LED pulse = 100 µs
PRF = 100 Hz
LED pulse = 100 µs
All four DYNAMIC bits set to 1
All four DYNAMIC bits set to 1
Figure 23. Receiver SNR over Nyquist Bandwidth vs
Dynamic Power-Down Duty Cycle
Figure 24. Receiver Input-Referred Noise over Nyquist
Bandwidth vs Dynamic Power-Down Duty Cycle
106
104
102
100
30
26
22
RF = 250 kꢀ
18
14
10
RF = 500 kꢀ
RF = 250 kꢀ
98
RF = 500 kꢀ
96
0
10
20
30
40
50
60
70
0
10
20
30
40
50
60
70
±20 ±10
±20 ±10
Temperature (deg C)
Temperature (deg C)
C021
C020
LED pulse = 100 µs Pleth current = 1 µA
LED pulse = 100 µs Pleth current = 1 µA
Figure 25. SNR in 20-Hz Bandwidth vs Temperature
(Tx-Rx Loopback)
Figure 26. Input-Referred Noise Current in 20-Hz BW vs
Temperature (TX-Rx Loopback)
106
105
104
103
102
101
20
Stg2Gain = 1
Stg2Gain = 1.5
Stg2Gain = 2
Stg2Gain = 3
Stg2Gain = 4
16
12
8
100
Stg2Gain = 1
99
98
97
96
Stg2Gain = 1.5
Stg2Gain = 2
Stg2Gain = 3
Stg2Gain = 4
4
0
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C023
C022
Stage 2 enabled
Stage 2 enabled
Figure 27. Receiver SNR over Nyquist Bandwidth vs
Duty Cycle (Different Stage 2 Gain Settings)
Figure 28. Receiver Input-Referred Noise Current over
Nyquist Bandwidth vs Duty Cycle
(Different Stage 2 Gain Settings)
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Typical Characteristics (continued)
At PRF = 100 Hz, 25% duty cycle, RF = 500 kΩ, CF is adjusted to keep TIA time constant at 1/10th of sampling duration, All
supplies at 3.3 V, 8-MHz external clock, CLKOUT tri-state, 1-µF capacitor on TX_REF and BG pins, detector CIN = 50 pF,
TX_REF = 0.5 V, ADC averaging = max allowed, and SNR in dBFS is noise referred to full-scale range of 2 V, unless
otherwise noted.
60
56
52
48
44
40
36
32
28
24
20
100
80
60
40
20
0
±20
3
4
5
6
7
0
50
100
150
200
250
300
Internal Clock Frequency (MHz)
DAC Current Setting Code
C029
C025
RF = 250 kΩ
PRF = 100 Hz
ADC averaging = 1
TX_REF = 0.25 V
Figure 30. Transmitter DAC Current Step Error
Figure 29. Receiver Input-Referred Noise Current vs
Internal Clock Frequency
116
112
108
25
TX_REF = 0.25 V
TX_REF = 0.5 V
TX_REF = 0.75 V
TX_REF = 1 V
20
15
10
5
TX_REF = 0.25 V
TX_REF = 0.5 V
TX_REF = 0.75 V
TX_REF = 1 V
104
100
96
0
0
5
10
15
20
25
0
5
10
15
20
25
Duty Cycle (%)
Duty Cycle (%)
C027
C028
PRF = 500 Hz
PRF = 500 Hz
DAC current is set such that ADC output is 50 %FS
DAC current is set such that ADC output is 50 %FS
Figure 31. SNR in 20-Hz BW vs Duty Cycle
(TX_REF Voltage with Tx-Rx Loopback)
Figure 32. Input Referred Noise Current in 20-Hz BW vs
Duty Cycle (TX_REF Voltage with Tx-Rx Loopback)
60
50
40
30
30
25
20
15
10
5
20
Actual current
Expected current - 2 %
10
Expected current + 2 %
0
0
0
50
100
150
200
250
300
44
45
46
47
48
49
50
51
52
DAC Current Setting Code
LED Current (mA)
C024
C031
TX_REF = 0.25 V
LED current = 48 mA
100 devices on tester
Figure 33. Transmitter Current linearity
Figure 34. Transmitter Current Across Devices
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Typical Characteristics (continued)
At PRF = 100 Hz, 25% duty cycle, RF = 500 kΩ, CF is adjusted to keep TIA time constant at 1/10th of sampling duration, All
supplies at 3.3 V, 8-MHz external clock, CLKOUT tri-state, 1-µF capacitor on TX_REF and BG pins, detector CIN = 50 pF,
TX_REF = 0.5 V, ADC averaging = max allowed, and SNR in dBFS is noise referred to full-scale range of 2 V, unless
otherwise noted.
100
DAC setting = 50 codes
80
60
40
20
0
DAC setting = 75 codes
DAC setting = 100 codes
0.25
0.5
0.75
1
TX_REF (V)
C026
Figure 35. Transmitter Current vs TX_REF Voltage
(Multiple DAC Settings)
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8 Detailed Description
8.1 Overview
The AFE4403 is a complete analog front-end (AFE) solution targeted for pulse oximeter applications. The device
consists of a low-noise receiver channel, an LED transmit section, and diagnostics for sensor and LED fault
detection. To ease clocking requirements and provide the low-jitter clock to the AFE, an oscillator is also
integrated that functions from an external crystal. The device communicates to an external microcontroller or host
processor using an SPI interface. The Functional Block Diagram section provides a detailed block diagram for
the AFE4403. The blocks are described in more detail in the following sections.
8.2 Functional Block Diagram
Device
Reference
CF
+ 1.2V
-
RF
Filter
+
+
Gain
+
Buffer
SPISTE
Digital
Filter
INP
INN
Stage 2
TIA
4G ADC
SPISIMO
CPO
SPI
SPISOMI
SCLK
RF
Control
CF
Photodiode
VCM
Timing
Connector
LED_DRV_SUP
c
TX3
TXN
LED Driver
AFE_PDN
ADC_RDY
RESET
LED Current
Control DAC
TXP
%
DNC(1)
DNC(1)
DNC(1)
Diagonostic
Signals
DIAG_END
OSC
Diagnostics
c
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8.3 Feature Description
8.3.1 Receiver Channel
This section describes the functionality of the receiver channel.
8.3.1.1 Receiver Front-End
The receiver consists of a differential current-to-voltage (I-V) transimpedance amplifier (TIA) that converts the
input photodiode current into an appropriate voltage, as shown in Figure 36. The feedback resistor of the
amplifier (RF) is programmable to support a wide range of photodiode currents. Available RF values include:
1 MΩ, 500 kΩ, 250 kΩ, 100 kΩ, 50 kΩ, 25 kΩ, and 10 kΩ.
The device is ideally suited as a front-end for a PPG (photoplethysmography) application. In such an application,
the light from the LED is reflected (or transmitted) from (or through) the various components inside the body
(such as blood, tissue, and so forth) and are received by the photodiode. The signal received by the photodiode
has three distinct components:
1. A pulsatile or ac component that arises as a result of the changes in blood volume through the arteries.
2. A constant dc signal that is reflected or transmitted from the time invariant components in the path of light.
This constant dc component is referred to as the pleth signal.
3. Ambient light entering the photodiode.
The ac component is usually a small fraction of the pleth component, with the ratio referred to as the perfusion
index (PI). Thus, the allowed signal chain gain is usually determined by the amplitude of the dc component.
Rx
SLED2
CONVLED2
LED2
CF
RF
RG
ADC
ADC Output Rate
PRF Sa/sec
Amb
LED1
+
+
Stage 2
Gain
SLED2_amb
SLED1
+
CONVLED2_amb
CONVLED1
TIA
CPD
Buffer
ûꢀꢀADC
RG
RF
CF
ADC Convert
ADC Clock
Amb
Ambient
DAC
CONVLED1_amb
SLED1_amb
I-V Amplifier
Filter
Buffer
ADC
Amb cancellation DAC
Ambient-cancellation current can be set digitally using SPI interface.
Figure 36. Receiver Front-End
The RF amplifier and the feedback capacitor (CF) form a low-pass filter for the input signal current. Always ensure
that the low-pass filter RC time constant has sufficiently high bandwidth (as shown by Equation 1) because the
input current consists of pulses. For this reason, the feedback capacitor is also programmable. Available CF
values include: 5 pF, 10 pF, 25 pF, 50 pF, 100 pF, and 250 pF. Any combination of these capacitors can also be
used.
Rx Sample Time
RF ´ CF £
10
(1)
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Feature Description (continued)
The output voltage of the I-V amplifier includes the pleth component (the desired signal) and a component
resulting from the ambient light leakage. The I-V amplifier is followed by the second stage, which consists of a
current digital-to-analog converter (DAC) that sources the cancellation current and an amplifier that gains up the
pleth component alone. The amplifier has five programmable gain settings: 0 dB, 3.5 dB, 6 dB, 9.5 dB, and
12 dB. The gained-up pleth signal is then low-pass filtered (500-Hz bandwidth) and buffered before driving a 22-
bit ADC. The current DAC has a cancellation current range of 10 µA with 10 steps (1 µA each). The DAC value
can be digitally specified with the SPI interface. Using ambient compensation with the ambient DAC allows the
dc-biased signal to be centered to near mid-point of the amplifier (±0.9 V). Using the gain of the second stage
allows for more of the available ADC dynamic range to be used.
The output of the ambient cancellation amplifier is separated into LED2 and LED1 channels. When LED2 is on,
the amplifier output is filtered and sampled on capacitor CLED2. Similarly, the LED1 signal is sampled on the
CLED1 capacitor when LED1 is on. In between the LED2 and LED1 pulses, the idle amplifier output is sampled to
estimate the ambient signal on capacitors CLED2_amb and CLED1_amb
.
The sampling duration is termed the Rx sample time and is programmable for each signal, independently. The
sampling can start after the I-V amplifier output is stable (to account for LED and cable settling times). The Rx
sample time is used for all dynamic range calculations; the minimum time recommended is 50 µs. While the
AFE4403 can support pulse widths lower than 50 us, having too low a pulse width could result in a degraded
signal and noise from the photodiode.
A single, 22-bit ADC converts the sampled LED2, LED1, and ambient signals sequentially. Each conversion
provides a single digital code at the ADC output. As discussed in the Receiver Timing section, the conversions
are meant to be staggered so that the LED2 conversion starts after the end of the LED2 sample phase, and so
on.
Note that four data streams are available at the ADC output (LED2, LED1, ambient LED2, and ambient LED1) at
the same rate as the pulse repetition frequency. The ADC is followed by a digital ambient subtraction block that
additionally outputs the (LED2 – ambient LED2) and (LED1 – ambient LED1) data values.
The model of the photodiode and the connection to the TIA is shown in Figure 37.
CF
RF
Sensor Model
VTIA
-
+
-
-
ADC
CIN
Iin
VTIA
+
+
CF
RF
Figure 37. TIA Block Diagram
Iin is the signal current generated by the photodiode in response to the incident light. Cin is the zero-bias
capacitance of the photodiode. The current-to-voltage gain in the TIA is given by Equation 2:
VTIA (diff) = VTIA+ – VTIA– = 2 × Iin × RF
(2)
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Feature Description (continued)
For example, for a photodiode current of Iin = 1 µA and a TIA gain setting of RF = 100 kΩ, the differential output
of the TIA is equal to 200 mV. The TIA has an operating range of ±1 V, and the ADC has an input full-scale
range of ±1.2 V (the extra margin is to prevent the ADC from saturating while operating the TIA at the fullest
output range). Furthermore, because the PPG signal is one-sided, only one half of the full-scale is used. TI
recommends operating the device at a dc level that is not more than 50% to 60% of the ADC full-scale. The
margin allows for sudden changes in the signal level that might saturate the signal chain if operating too close to
full-scale. Signal levels are shown in Figure 38:
+1.2 V
ADC max
(Differential)
+1 V
TIA max
(Differential)
+0.6 V
Ideal Operating
Point
0 V
-1 V
TIA min
(Differential)
-1.2 V
ADC min
(Differential)
Figure 38. Signal Levels in TIA and ADC
On startup, a gain calibration algorithm running on the microcontroller unit (MCU) can be used to monitor the dc
level and adjusts the LED current and TIA gain to get close to the target dc level. In addition to a target dc level,
a high and low threshold (for example 80% and 20% of full-scale) can be determined that can cause the
algorithm to switch to a different TIA gain or LED current setting when the signal amplitude changes beyond
these thresholds.
In heart rate monitoring (HRM) applications demanding small-form factors, the sensor size can be so small (and
the signal currents so low) that they do not occupy even 50% of full-scale even with the highest TIA gain setting
of 1 MΩ, which is the case for signal currents that are less than 300 nA. As such, experimentation with various
use cases is essential in order to determine the optimal target value, as well as high and low thresholds. Also, by
enabling the stage 2 and introducing additional gain (up to 12 dB), a few extra decibels of SNR can be achieved.
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Feature Description (continued)
8.3.1.2 Ambient Cancellation Scheme and Second Stage Gain Block
The receiver provides digital samples corresponding to ambient duration. The host processor (external to the
AFE) can use these ambient values to estimate the amount of ambient light leakage. The processor must then
set the value of the ambient cancellation DAC using the SPI, as shown in Figure 39.
Device
Host Processor
LED2 Data
ADC Output Rate
PRF Samples per Second
Ambient (LED2)
Data
Front End
(LED2 ± Ambient)
Data
Ambient Estimation Block
SPI
Interface
Ambient information is available in the host
processor.
ADC
Rx
SPI
Digital
Block
The processor can:
* Read ambient data
LED1 Data
Ambient (LED1)
Data
* Estimate ambient value to
be cancelled
* Set the value to be used by the ambient
cancellation DAC using the SPI of AFE
(LED1 ± Ambient)
Data
Digital Control for Ambient-Cancellation DAC
Figure 39. Ambient Cancellation Loop (Closed by the Host Processor)
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Feature Description (continued)
Using the set value, the ambient cancellation stage subtracts the ambient component and gains up only the pleth
component of the received signal; see Figure 40. The amplifier gain is programmable to 0 dB, 3.5 dB, 6 dB,
9.5 dB, and 12 dB.
ICANCEL
Cf
Rg
Rf
IPLETH + IAMB
Ri
Rx
VDIFF
Ri
Rf
Rg
ICANCEL
Cf
Value of ICANCEL set using
the SPI interface.
Figure 40. Front-End (I-V Amplifier and Cancellation Stage)
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Feature Description (continued)
The differential output of the second stage is VDIFF, as given by Equation 3:
RF
RF
VDIFF = 2 ´ IPLETH
´
+ IAMB
´
- ICANCEL ´ RG
RI
RI
where:
•
•
•
•
RI = 100 kΩ,
IPLETH = photodiode current pleth component,
IAMB = photodiode current ambient component, and
ICANCEL = the cancellation current DAC value (as estimated by the host processor).
(3)
RG values with various gain settings are listed in Table 1.
Table 1. RG Values
GAIN
0 (x1)
RG(kΩ)
100
3.5 (x1.5)
6 (x2)
150
200
9.5 (x3)
12 (x4)
300
400
8.3.1.3 Receiver Control Signals
LED2 sample phase (SLED2 or SR): When this signal is high, the amplifier output corresponds to the LED2 on-
time. The amplifier output is filtered and sampled into capacitor CLED2. To avoid settling effects resulting from the
LED or cable, program SLED2 to start after the LED turns on. This settling delay is programmable.
Ambient sample phase (SLED2_amb or SR_amb): When this signal is high, the amplifier output corresponds to the
LED2 off-time and can be used to estimate the ambient signal (for the LED2 phase). The amplifier output is
filtered and sampled into capacitor CLED2_amb
.
LED1 sample phase (SLED1 or SIR): When this signal is high, the amplifier output corresponds to the LED1 on-
time. The amplifier output is filtered and sampled into capacitor CLED1. To avoid settling effects resulting from the
LED or cable, program SLED1 to start after the LED turns on. This settling delay is programmable.
Ambient sample phase (SLED1_amb or SIR_amb): When this signal is high, the amplifier output corresponds to the
LED1 off-time and can be used to estimate the ambient signal (for the LED1 phase). The amplifier output is
filtered and sampled into capacitor CLED1_amb
.
LED2 convert phase (CONVLED2 or CONVR): When this signal is high, the voltage sampled on CLED2 is buffered
and applied to the ADC for conversion. At the end of the conversion, the ADC provides a single digital code
corresponding to the LED2 sample.
Ambient convert phases (CONVLED2_amb or CONVR_amb, CONVLED1_ambor CONVIR_amb): When this signal is
high, the voltage sampled on CLED2_amb (or CLED1_amb) is buffered and applied to the ADC for conversion. At the
end of the conversion, the ADC provides a single digital code corresponding to the ambient sample.
LED1 convert phase (CONVLED1 or CONVIR): When this signal is high, the voltage sampled on CLED1 is
buffered and applied to the ADC for conversion. At the end of the conversion, the ADC provides a single digital
code corresponding to the LED1 sample.
8.3.1.4 Receiver Timing
See Figure 41 for a timing diagram detailing the control signals related to the LED on-time, Rx sample time, and
the ADC conversion times for each channel. Figure 41 shows the timing for a case where each phase occupies
25% of the pulse repetition period. However, this percentage is not a requirement. In cases where the device is
operated with low pulse repetition frequency (PRF) or low LED pulse durations, the active portion of the pulse
repetition period can be reduced. Using the dynamic power-down feature, the overall power consumption can be
significantly reduced.
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Red LED
ON signal
TLED LED ON time
<= 0.25T
IR LED
ON signal
N+1
Plethysmograph signal
N+2
N
Photo-diode current
Or
N
N+1
I-V output pulses
Ambient level
(dark level)
Rx sample time
= TLED ± settle time
SR,
Sample Red
SR_amb
,
Sample Ambient
(red phase)
SIR,
Sample IR
SIR_amb
,
Sample Ambient
(IR phase)
CONVIR_amb
,
Convert ambient sample
(IR phase)
CONVR,
Convert red sample
CONVR_amb
,
Convert ambient sample
(red phase)
CONVIR,
Convert IR sample
ADC Conversion
Pulse repetition period T = 1/PRF
TCONV
Sample phase ± input current is converted to an analog voltage.
Sample phase width is variable from 0 to 25% duty cycle
Convert phase ± sampled analog voltage is converted to a digital code
NOTE: Relationship to the AFE4403 EVM is: LED1 = IR and LED2 = RED.
Figure 41. Rx Timing Diagram
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8.3.2 Clocking and Timing Signal Generation
The crystal oscillator generates a master clock signal using an external crystal. In the default mode, a divide-by-2
block converts the 8-MHz clock to 4 MHz, which is used by the AFE to operate the timer modules, ADC, and
diagnostics. The 4-MHz clock is buffered and output from the AFE in order to clock an external microcontroller.
The clocking functionality is shown in Figure 42.
Timer
Module
Divide-
by-2
ADC
Diagnostics
Module
Oscillator
XIN
XOUT
CLKOUT
4 MHz
8-MHz Crystal
Figure 42. AFE Clocking
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To enable flexible clocking, the AFE4403 has a clock divider with programmable division ratios. While the default
division ratio is divide-by-2, the clock divider can be programmed to select between ratios of 1, 2, 4, 6, 8, or 12.
The division ratio should be selected based on the external clock input frequency such that the divided clock has
a frequency close to 4 MHz. For this reason, CLKOUT is referred as a 4-MHz clock in this document. When
operating with an external clock input, the divider is reset based on the RESET rising edge. Figure 43 shows the
case where the divider ratio is set to divide-by-2.
Tres_setup
CLK input (on XIN)
RESET
CLKOUT
Figure 43. Clock Divider Reset
The device supports both external clock mode as well as an internal clock mode with external crystal.
In the external clock mode, an external clock is input on the XIN pin and the device internally generates the
internal clock (used by the timing engine and the ADC) by a programmable division ratio. After division, the
internal clock should be within a range of 4 MHz to 6 MHz. The exact frequency of this divided clock is one of the
pieces of information required to establish the heart rate being measured from the pulse data.
In internal clock mode, an external crystal (connected between XIN and XOUT) is used to generate the clock. To
generate sustained oscillations, the oscillator within the AFE provides negative resistance to cancel out the ESR
of the crystal. A good rule of thumb is to limit the ESR of the crystal to less than a third of the negative resistance
achievable by the oscillator. Figure 44 shows the connection of Crystal to AFE4403.
OSCILLATOR
XIN
C1
XOUT
C2
8 MHz crystal
(Csh, ESR)
Figure 44. Connection of Crystal to AFE4403
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In Figure 44 the crystal is characterized by a capacitance, Csh (shunt capacitance of the crystal) and an
equivalent series resistance (ESR). C1 and C2 are external capacitors added at the XIN and XOUT pins.
The negative resistance achievable from the internal oscillator is given by Equation 4:
R = –1 / (2 × ω × Csh × [1 + Csh / CL])
where
•
•
•
•
CL = (C1 × C2) / (C1 + C2),
ω is the frequency of oscillation in rads,
Csh is the shunt capacitor of the crystal, and
C1, C2 are the capacitors to ground from the XIN, XOUT pins. A value of approximately 15 pF is recommended for
C1, C2.
(4)
For example, with Csh = 8 pF, C1 = C2 = 15 pF, and a frequency of 8 MHz, the result is Equation 5:
R = –600 Ω
(5)
Thus, the crystal ESR is limited to less than approximately 200 Ω.
TI highly recommends that a single clock source be used to generate the clock required by the AFE as well as
the clock needed by the microcontroller (MCU). If an independent clock source is used by the MCU, then any
energy coupling into the AFE supply or ground or input pins can cause aliased spurious tones close to the heart
rate being measured. To enable operation with the single clock source between the AFE and the MCU, two
options are possible:
1. AFE clock as master: The AFE uses a crystal to generate its clock. CLKOUT from the AFE is used as the
input clock for the MCU.
2. MCU clock as master: The AFE operates with an external clock provided by the MCU.
Note that the switching of CLKOUT consumes power. Thus, if CLKOUT is not used, it can be shut off using the
CLKOUT_TRI bit.
8.3.3 Timer Module
See Figure 45 for a timing diagram detailing the various timing edges that are programmable using the timer
module. The rising and falling edge positions of 11 signals can be controlled. The module uses a single 16-bit
counter (running off of the 4-MHz clock) to set the time-base.
All timing signals are set with reference to the pulse repetition period (PRP). Therefore, a dedicated compare
register compares the 16-bit counter value with the reference value specified in the PRF register. Every time that
the 16-bit counter value is equal to the reference value in the PRF register, the counter is reset to 0.
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LED2(Red LED)
ON signal
tLED LED On-Time
d 0.25 T
LED1(IR LED)
ON signal
Rx Sample Time = tLED ± Settling Time
SLED2_amb
,
Sample Ambient
(LED2(Red) phase)
SLED1
,
Sample LED1(IR)
SLED1_amb
,
Sample Ambient
(LED1(IR) phase)
SLED2
,
Sample LED2(Red)
CONVLED2
,
Convert LED2(Red) sample
CONVLED2_amb
,
Convert ambient sample
(LED2(Red) phase)
CONVLED1
,
Convert LED1(IR) sample
CONVLED1_amb
,
Convert ambient sample
(LED1(IR) phase)
ADC Conversion
ADC Reset
ADC_RDY Pin
Pulse Repetition Period (PRP)
T = 1 / PRF
NOTE: Programmable edges are shown in blue and red.
Figure 45. AFE Control Signals
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For the timing signals in Figure 41, the start and stop edge positions are programmable with respect to the PRF
period. Each signal uses a separate timer compare module that compares the counter value with
preprogrammed reference values for the start and stop edges. All reference values can be set using the SPI
interface.
After the counter value has exceeded the stop reference value, the output signal is set. When the counter value
equals the stop reference value, the output signal is reset. Figure 46 shows a diagram of the timer compare
register. With a 4-MHz clock, the edge placement resolution is 0.25 µs.
Set
START
STOP
Start Reference Register
Output
Signal
Counter
Input
Reset
Stop Reference Register
Timer Compare Register
Enable
Figure 46. Compare Register
The ADC conversion signal requires four pulses in each PRF clock period. Timer compare register 11 uses four
sets of start and stop registers to control the ADC conversion signal, as shown in Figure 47.
Reset
CLKIN
16-Bit Counter
Reset
Enable
Counter
S
R
Start
Stop
PRF
Pulse
Timer Compare
16-Bit Register 1
Timer Compare
16-Bit PRF Register
RED LED
IR LED
En
En
En
En
En
En
En
S
R
Start
Stop
S
R
Start
Stop
CONVR,
Convert RED Sample
Timer Compare
16-Bit Register 2
Timer Compare
16-Bit Register 7
S
R
Start
Stop
S
R
SR
Start
Stop
CONVIR
,
Timer Compare
16-Bit Register 3
Timer Compare
16-Bit Register 8
Sample RED
Convert IR Sample
En
CONVIR_amb
,
S
R
Start
Stop
S
R
SIR
Sample IR
Start
Stop
Timer Compare
16-Bit Register 4
Timer Compare
16-Bit Register 9
Convert Ambient Sample
(IR Phase)
En
En
CONVR_amb
,
S
R
S
R
Start
Stop
Start
Stop
Timer Compare
16-Bit Register 5
Timer Compare
16-Bit Register 10
Convert Ambient Sample
(RED Phase)
SR_amb
,
Sample Ambient
(red phase)
START-A
STOP-A
S
R
Start
Stop
SIR_amb
Sample Ambient
(IR phase)
,
Timer Compare
16-Bit Register 6
En
START-B
STOP-B
ADC
Timer Compare
Conversion
16-Bit Register 11
START-C
STOP-D
START-D
STOP-D
En
Timer Module
Figure 47. Timer Module
8.3.3.1 Using the Timer Module
The timer module registers can be used to program the start and end instants in units of 4-MHz clock cycles.
These timing instants and the corresponding registers are listed in Table 2.
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Note that the device does not restrict the values in these registers; thus, the start and end edges can be
positioned anywhere within the pulse repetition period. Care must be taken by the user to program suitable
values in these registers to avoid overlapping the signals and to make sure none of the edges exceed the value
programmed in the PRP register. Writing the same value in the start and end registers results in a pulse duration
of one clock cycle. The following steps describe the timer sequencing configuration:
1. With respect to the start of the PRP period (indicated by timing instant t0 in Figure 48), the following
sequence of conversions must be followed in order: convert LED2 → LED2 ambient → LED1 → LED1
ambient.
2. Also, starting from t0, the sequence of sampling instants must be staggered with respect to the respective
conversions as follows: sample LED2 ambient → LED1 → LED1 ambient → LED2.
3. Finally, align the edges for the two LED pulses with the respective sampling instants.
Table 2. Clock Edge Mapping to SPI Registers
TIME INSTANT
(See Figure 48 and
EXAMPLE(2)
(Decimal)
Figure 49)(1)
DESCRIPTION
Start of pulse repetition period
Start of sample LED2 pulse
End of sample LED2 pulse
Start of LED2 pulse
CORRESPONDING REGISTER ADDRESS AND REGISTER BITS
No register control
t0
t1
—
LED2STC[15:0], register 01h
6050
7998
6000
7999
50
t2
LED2ENDC[15:0], register 02h
LED2LEDSTC[15:0], register 03h
LED2LEDENDC[15:0], register 04h
ALED2STC[15:0], register 05h
t3
t4
End of LED2 pulse
t5
Start of sample LED2 ambient pulse
End of sample LED2 ambient pulse
Start of sample LED1 pulse
End of sample LED1 pulse
Start of LED1 pulse
t6
ALED2ENDC[15:0], register 06h
LED1STC[15:0], register 07h
1998
2050
3998
2000
3999
4050
5998
t7
t8
LED1ENDC[15:0], register 08h
LED1LEDSTC[15:0], register 09h
LED1LEDENDC[15:0], register 0Ah
ALED1STC[15:0], register 0Bh
ALED1ENDC[15:0], register 0Ch
t9
t10
t11
t12
End of LED1 pulse
Start of sample LED1 ambient pulse
End of sample LED1 ambient pulse
LED2CONVST[15:0], register 0Dh
Must start one AFE clock cycle after the ADC reset pulse ends.
t13
t14
t15
t16
t17
t18
t19
Start of convert LED2 pulse
4
End of convert LED2 pulse
LED2CONVEND[15:0], register 0Eh
1999
2004
3999
4004
5999
6004
ALED2CONVST[15:0], register 0Fh
Must start one AFE clock cycle after the ADC reset pulse ends.
Start of convert LED2 ambient pulse
End of convert LED2 ambient pulse
Start of convert LED1 pulse
ALED2CONVEND[15:0], register 10h
LED1CONVST[15:0], register 11h
Must start one AFE clock cycle after the ADC reset pulse ends.
End of convert LED1 pulse
LED1CONVEND[15:0], register 12h
ALED1CONVST[15:0], register 13h
Must start one AFE clock cycle after the ADC reset pulse ends.
Start of convert LED1 ambient pulse
t20
t21
t22
t23
End of convert LED1 ambient pulse
ALED1CONVEND[15:0], register 14h
ADCRSTSTCT0[15:0], register 15h
ADCRSTENDCT0[15:0], register 16h
7999
0
Start of first ADC conversion reset pulse
End of first ADC conversion reset pulse(3)
3
Start of second ADC conversion reset pulse ADCRSTSTCT1[15:0], register 17h
2000
End of second ADC conversion reset
ADCRSTENDCT1[15:0], register 18h
pulse(3)
t24
2003
t25
t26
t27
t28
t29
Start of third ADC conversion reset pulse
End of third ADC conversion reset pulse(3)
Start of fourth ADC conversion reset pulse
ADCRSTSTCT2[15:0], register 19h
ADCRSTENDCT2[15:0], register 1Ah
ADCRSTSTCT3[15:0], register 1Bh
4000
4003
6000
6003
7999
End of fourth ADC conversion reset pulse(3) ADCRSTENDCT3[15:0], register 1Ch
End of pulse repetition period PRPCOUNT[15:0], register 1Dh
(1) Any pulse can be set to zero width by making its start value higher than the end value.
(2) Values are based off of a pulse repetition frequency (PRF) = 500 Hz and duty cycle = 25%.
(3) See Figure 49, note 2 for the effect of the ADC reset time crosstalk.
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LED2 (RED LED)
On Signal
t3
t4
LED1 (IR LED)
On Signal
t9
t10
SLED2_amb
Sample Ambient
LED2 (RED) Phase
,
t6
t5
SLED1
,
Sample LED1 (IR)
t7
t8
SLED1_amb
,
Sample Ambient
LED1 (IR) Phase
t11
t12
SLED2
,
Sample LED2 (RED)
t1
t2
CONVLED2
,
t14
t13
Convert LED2 (RED) Sample
CONVLED2_amb
,
Convert Ambient Sample
LED2 (RED) Phase
t15
t16
CONVLED1
,
t17
Convert LED1 (IR) Sample
t18
CONVLED1_amb
,
Convert Ambient Sample
LED1 (IR) Phase
t19
t20
ADC Conversion
ADC Reset
t23
t25
t27
t21
t22
t24
t26
t28
Pulse Repetition Period (PRP),
One Cycle
t0
t29
(1) RED = LED2, IR = LED1.
(2) A low ADC reset time can result in a small component of the LED signal leaking into the ambient phase. With an ADC reset of two clock
cycles, a –60-dB leakage is expected. In many cases, this leakage does not affect system performance. However, if this crosstalk must be
completely eliminated, a longer ADC reset time of approximately six clock cycles is recommended for t22, t24, t26, and t28
.
Figure 48. Programmable Clock Edges(1)(2)
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t14
CONVLED2
Convert LED2 (RED) Sample
,
t13
CONVLED2_amb
Convert Ambient Sample
LED2 (RED) Phase
,
t16
t15
t18
CONVLED1
Convert LED1 (IR) Sample
,
t17
CONVLED1_amb
Convert Ambient Sample
LED1 (IR) Phase
,
t20
t19
ADC Conversion
Two 4-MHz Clock Cycles
t21
t23
t25
t27
t22
ADC Reset
t24
t28
t26
Pulse Repetition Period (PRP),
One Cycle
t0
t29
(1) RED = LED2, IR = LED1.
(2) A low ADC reset time can result in a small component of the LED signal leaking into the ambient phase. With an ADC reset of two clock
cycles, a –60-dB leakage is expected. In many cases, this leakage does not affect system performance. However, if this crosstalk must be
completely eliminated, a longer ADC reset time of approximately six clock cycles is recommended for t22, t24, t26, and t28
.
Figure 49. Relationship Between the ADC Reset and ADC Conversion Signals(1)(2)
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8.3.4 Receiver Subsystem Power Path
The block diagram in Figure 50 shows the AFE4403 Rx subsystem power routing. Internal LDOs running off
RX_ANA_SUP and RX_DIG_SUP generate the 1.8-V supplies required to drive the internal blocks. The two
receive supplies could be shorted to a single supply on the board.
1.8 V
RX_ANA_SUP to
RX_ANA_SUP
1.8-V Regulator
Rx Analog Modules
RX_DIG_SUP to
1.8 V
RX_DIG_SUP
1.8-V Regulator
Rx I/O
Block
I/O
Pins
Rx Digital
Device
Figure 50. Receive Subsystem Power Routing
8.3.5 Transmit Section
The transmit section integrates the LED driver and the LED current control section with 8-bit resolution.
The RED and IR LED reference currents can be independently set. The current source (ILED) locally regulates
and ensures that the actual LED current tracks the specified reference. The transmitter section uses an internal
0.25-V reference voltage for operation. This reference voltage is available on the TX_REF pin and must be
decoupled to ground with a 2.2-μF capacitor. The TX_REF voltage is derived from the TX_CTRL_SUP. The
TX_REF voltage can be programmed from 0.25 V to 1 V. A lower TX_REF voltage allows a lower voltage to be
supported on LED_DRV_SUP. However, the transmitter dynamic range falls in proportion to the voltage on
TX_REF. Thus, a TX_REF setting of 0.5 V gives a 6-dB lower transmitter dynamic range as compared to a 1-V
setting on TX_REF, and a 6-dB higher transmitter dynamic range as compared to a 0.25-V setting on TX_REF.
Note that reducing the value of the band-gap reference capacitor on the BG pin reduces the time required for the
device to wake-up and settle. However, this reduction in time is a trade-off between wake-up time and noise
performance.For example, reducing the value of the capacitors on the BG and TX_REF pins from 2.2 uF to 0.1
uF reduces the wake-up time (from complete power-down) from 1000 ms to 100 ms, but results in a few decibels
of degradation in the transmitter dynamic range.
The minimum LED_DRV_SUP voltage required for operation depends on:
•
•
Voltage drop across the LED (VLED),
Voltage drop across the external cable, connector, and any other component in series with the LED (VCABLE),
and
•
Transmitter reference voltage.
See the Recommended Operating Conditions table for further details.
Two LED driver schemes are supported:
•
•
An H-bridge drive for a two-terminal back-to-back LED package; see Figure 51.
A push-pull drive for a three-terminal LED package; see Figure 52.
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LED_DRV_SUP
TX_CTRL_SUP
External
Supply
Tx
CBULK
H-Bridge
LED2_ON
LED1_ON
H-Bridge
Driver
LED2_ON
or
LED1_ON
LED2 Current
Reference
LED
Current
Control
ILED
8-Bit Resolution
LED1 Current
Reference
Register
Register
LED2 Current Reference
LED1 Current Reference
Figure 51. Transmit: H-Bridge Drive
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TX_CTRL_SUP
LED_DRV_SUP
External
Supply
CBULK
Tx
LED2_ON
LED1_ON
H-Bridge
Driver
LED2_ON
or
LED1_ON
LED2 Current
Reference
LED
Current
Control
ILED
8-Bit Resolution
LED1 Current
Reference
Register
Register
RED Current Reference
IR Current Reference
Figure 52. Transmit: Push-Pull LED Drive for Common Anode LED Configuration
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8.3.5.1 Third LED Support
A third LED can be optionally connected on the TX3 pin, as shown in Figure 53. An example application involving
a third LED is where the Red and IR LEDs are connected on the TXP, TXN pins for pulse oximeter applications
and a third LED (for example a Green LED) is connected on the TX3 pin for a heart rate monitoring application.
The third LED can be connected only in common anode configuration. By programming the TX3_MODE register
bit, the timing engine controls on TXP can be transferred to the TX3 pin. In this mode, the register bits that
indicate the diagnostic results on the TXP pin now indicate the diagnostic results on the TX3 pin. The selection
between using TX3 versus using TXP, TXN is intended as a static mode selection as opposed to a dynamic
switching selection. A typical time delay of approximately 20 ms is required for the receive channel to settle after
a change to the TX3_MODE setting. During this transition time, the receive signal chain should be active so that
the filters are able to settle to the new signal level from the third LED.
Figure 53. Multiplexing Third LED
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8.3.5.2 Transmitter Power Path
The block diagram in Figure 54 shows the AFE4403 Tx subsystem power routing.
TX_CTRL_SUP
Tx Reference
and
Control
LED_DRV_SUP
LED
Current
Control
DAC
Tx LED
Bridge
Device
Figure 54. Transmit Subsystem Power Routing
8.3.5.3 LED Power Reduction During Periods of Inactivity
The diagram in Figure 55 shows how LED bias current passes 50 µA whenever LED_ON occurs. In order to
minimize power consumption in periods of inactivity, the LED_ON control must be turned off. Furthermore, the
TIMEREN bit in the CONTROL1 register should be disabled by setting the value to 0.
Note that depending on the LEDs used, the LED may sometimes appear dimly lit even when the LED current is
set to 0 mA. This appearance is because of the switching leakage currents (as shown in Figure 55) inherent to
the timer function. The dimmed appearance does not effect the ambient light level measurement because during
the ambient cycle, LED_ON is turned off for the duration of the ambient measurement.
0 mA to 50 mA
(See the LEDRANGE bits
in the LEDCNTRL register.)
1 PA
50 PA
LED_ON
Figure 55. LED Bias Current
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8.3.5.4 LED Configurations
Multiple LED configurations are possible with the AFE4403.
Case 1: Red, IR LEDs in the common anode configuration for SPO2 and a Green LED for the HRM. Figure 56
shows the common anode configuration for this case. Figure 57 shows the configuration for HRM mode.
LED_DRV_SUP
Max
100mA
Max
100mA
OFF
RED
IR
TX3
TXM
TXP
LED1
Controls
LED2
Controls
LED_DRV_GND
Figure 56. SPO2 Application, Common Anode Configuration
HRM mode: Set TX3_MODE = 1.
LED_DRV_SUP
Max 50mA
RED
IR
OFF
TX3
TXM
TXP
To disable the IR
LED, set LED1
FRQWUROVꢀWRꢀµ0¶.
LED2
Controls
LED1
Controls
LED_DRV_GND
Figure 57. HRM Application Using the Third LED (Optional use of the IR LED)
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Case 2: Red, IR LEDs in an H-bridge configuration for SPO2 and a Green LED for the HRM. The H-bridge
configuration for this case is shown in Figure 58. Figure 59 shows the configuration for HRM mode.
SPO2 mode: Set TX3_MODE = 0.
LED_DRV_SUP
LED2
LED1
Controls
Controls
LED_DRV_SUP
IR
Max 100mA
Max 100mA
OFF
TXM
TXP
TX3
RED
LED2
LED1
Controls
Controls
LED_DRV_GND
Figure 58. SPO2 Application, H-Bridge Configuration
HRM mode: Set TX3_MODE = 1.
LED_DRV_SUP
LED_DRV_SUP
LED1
Controls
IR
Max 50mA
TXM
TXP
TX3
OFF
RED
LED2
Controls
To disable the IR
LED, set LED1
FRQWUROVꢀWRꢀµ0¶.
LED1
Controls
LED_DRV_GND
LED_DRV_GND
Figure 59. HRM Application Using the Third LED
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Case 3: Driving two LEDs simultaneously for HRM.
Some sensor modules have two LEDs on either side of the photodiode to make the illumination more uniform.
The two LEDs can be connected in parallel, as shown in Figure 60.
The connection shown in Figure 60 results in an equal split of the current between the two LEDs if their forward
voltages are exactly matched. High mismatch in the forward voltages of the two LEDs can cause one of them to
consume the majority of the current.
LED_DRV_SUP
TXP
TXM
TX3
Max
100mA
LED2
Controls
LED1
Controls
LED_DRV_GND
Figure 60. Using Two Parallel LEDs for an HRM Application
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Case 4: Driving two LEDs separated in time for HRM.
The two LEDs can also be driven as shown in Figure 61.
While this mode of driving the two LEDs does not drive them simultaneously, there are two advantages in this
case. First, the full current is available for driving each LED. Secondly, the mismatch in the forward voltages
between the two LEDs does not play a role.
LED_DRV_SUP
TX3
TXM
TXP
Max
Max
100mA
100mA
TX3
LED2
Controls
LED1
Controls
LED_DRV_GND
Figure 61. Using Two Parallel LEDs for an HRM Application with Separation in Timing
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8.4 Device Functional Modes
8.4.1 ADC Operation and Averaging Module
After the falling edge of the ADC reset signal, the ADC conversion phase starts (refer to Figure 49). Each ADC
conversion takes 50 µs.
The ADC operates with averaging. The averaging module averages multiple ADC samples and reduces noise to
improve dynamic range. Figure 62 shows a diagram of the averaging module. The ADC output is a 22-bit code
that is obtained by discarding the two MSBs of the 24-bit registers (for example the register with address 2Ah),
as shown in Figure 63.
Rx Digital
ADC Reset
22-Bits
ADC Output Rate
PRF Samples per Second
Register
42
LED2 Data
LED2 Data
ADC
Register
43
Ambient
(LED2) Data
LED2_Ambient Data
ADC
Averager
Register
44
LED1 Data
LED1 Data
ADC Reset
Ambient
(LED1) Data
Register
45
LED1_Ambient Data
ADC Convert
ADC Clock
Figure 62. Averaging Module
Figure 63. 22-Bit Word
23
11
22
21
9
20
8
19
18
17
16
15
14
2
13
1
12
0
Ignore
22-Bit ADC Code, MSB to LSB
10
7
6
5
4
3
22-Bit ADC Code, MSB to LSB
Table 3 shows the mapping of the input voltage to the ADC to its output code.
Table 3. ADC Input Voltage Mapping
DIFFERENTIAL INPUT VOLTAGE AT ADC INPUT
22-BIT ADC OUTPUT CODE
1000000000000000000000
1111111111111111111111
0000000000000000000000
0000000000000000000001
0111111111111111111111
–1.2 V
(–1.2 / 221) V
0
(1.2 / 221) V
1.2 V
The data format is binary twos complement format, MSB-first. Because the TIA has a full-scale range of ±1 V, TI
recommends that the input to the ADC does not exceed ±1 V, which is approximately 80% of its full-scale.
In cases where having the processor read the data as a 24-bit word instead of a 22-bit word is more convenient,
the entire register can be mapped to the input level as shown in Figure 64.
Figure 64. 24-Bit Word
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
24-Bit ADC Code, MSB to LSB
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Table 4 shows the mapping of the input voltage to the ADC to its output code when the entire 24-bit word is
considered.
Table 4. Input Voltage Mapping
DIFFERENTIAL INPUT VOLTAGE AT ADC INPUT
24-BIT ADC OUTPUT CODE
111000000000000000000000
111111111111111111111111
000000000000000000000000
000000000000000000000001
000111111111111111111111
–1.2 V
(–1.2 / 221) V
0
(1.2 / 221) V
1.2 V
Now the data can be considered as a 24-bit data in binary twos complement format, MSB-first. The advantage of
using the entire 24-bit word is that the ADC output is correct, even when the input is over the normal operating
range.
8.4.1.1 Operation Without Averaging
In this mode, the ADC outputs a digital sample one time for every 50 µs. Consider a case where the ADC_RDY
signals are positioned at 25%, 50%, 75%, and 100% points in the pulse repetition period. At the next rising edge
of the ADC reset signal, the first 22-bit conversion value is written into the result registers sequentially as follows
(see Figure 65):
•
•
•
•
At the 25% reset signal, the first 22-bit ADC sample is written to register 2Ah.
At the 50% reset signal, the first 22-bit ADC sample is written to register 2Bh.
At the 75% reset signal, the first 22-bit ADC sample is written to register 2Ch.
At the next 0% reset signal, the first 22-bit ADC sample is written to register 2Dh. The contents of registers
2Ah and 2Bh are written to register 2Eh and the contents of registers 2Ch and 2Dh are written to register
2Fh.
At the rising edge of the ADC_RDY signal, the contents of all six result registers can be read out.
8.4.1.2 Operation With Averaging
In this mode, all ADC digital samples are accumulated and averaged after every 50 µs. At the next rising edge of
the ADC reset signal, the average value (22-bit) is written into the output registers sequentially, as follows (see
Figure 66):
•
•
•
•
At the 25% reset signal, the averaged 22-bit word is written to register 2Ah.
At the 50% reset signal, the averaged 22-bit word is written to register 2Bh.
At the 75% reset signal, the averaged 22-bit word is written to register 2Ch.
At the next 0% reset signal, the averaged 22-bit word is written to register 2Dh. The contents of registers 2Ah
and 2Bh are written to register 2Eh and the contents of registers 2Ch and 2Dh are written to register 2Fh.
At the rising edge of the ADC_RDY signal, the contents of all six result registers can be read out.
The number of samples to be used per conversion phase is specified in the CONTROL1 register (NUMAV[7:0]).
The user must specify the correct value for the number of averages, as described in Equation 6:
0.25 ´ Pulse Repetition Period
NUMAV[7:0] + 1 =
- 1
50 ms
(6)
Note that the 50-µs factor corresponds to a case where the internal clock of the AFE (after division) is exactly
equal to 4 MHz. The factor scales linearly with the clock period being used.
When the number of averages is 0, the averaging is disabled and only one ADC sample is written to the result
registers.
Note that the number of average conversions is limited by 25% of the PRF. For example, eight samples can be
averaged with PRF = 625 Hz, and four samples can be averaged with PRF = 1250 Hz.
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ADC Conversion
ADC Data
1
2
3
4
5
6
7
8
9
10 11 12
13 14 15 16
17 18 19 20
ADC Reset
0%
75%
50%
25%
0%
ADC Data 1 are
written into
register 42.
ADC Data 9 are
written into
register 44.
ADC Data 5 are
written into
register 43.
ADC Data 13 are written into
register 45.
Register 42 ꢀ register 43
are written into register 46.
Register 44 ꢀꢁregister 45
are written into register 47.
ADC_RDY Pin
Pulse Repetition Period (PRP)
T = 1 / PRF
1.0 T
0 T
Figure 65. ADC Data Without Averaging (When Number of Averages = 0)
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ADC Conversion
ADC Data
1
2
3
4
5
6
7
8
9
10 11 12
13 14 15 16
17 18 19 20
ADC Reset
0%
75%
50%
25%
Average of
ADC data 1 to 3 are
written into
0%
Average of
ADC data 5 to 7
are written into
register 43.
Average of
ADC data 9 to 11 are
written into
Average of
ADC data 13 to 15 are written
into register 45.
register 42.
register 44.
Register 42 ꢀ register 43
are written into register 46.
Register 44 ꢀꢁregister 45
are written into register 47.
ADC_RDY Pin
Pulse Repetition Period
T = 1 / PRF
1.0 T
0 T
NOTE: Example is with three averages. The value of the NUMAVG[7:0] register bits = 2.
Figure 66. ADC Data with Averaging Enabled
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8.4.1.3 Dynamic Power-Down Mode
When operated at low PRF, a dynamic power-down mode can be optionally enabled to shut off blocks during a
portion of each period. This operation is illustrated in Figure 67. The dynamic power-down signal (called
PDN_CYCLE) can be internally generated using the timing controller. PDN_CYCLE can be used to shut off
power to internal blocks during the unused section within each pulse repetition period.
Pulse repetition period
Sample LED2
Sample Ambient 2
Sample LED1
Sample Ambient 1
Convert LED2
Convert Ambient 2
Convert LED1
Convert Ambient 1
PDN_CYCLE
t1
t2
Figure 67. Dynamic Power-Down Mode Timing
t1 and t2 denote the timing margin between the active portion of the period and the dynamic power-down signal.
TI recommends setting t1 > 50 µs and t2 > 200 µs in order to ensure sufficient time for the shutdown blocks to
recover from power-down. By choosing the blocks that are shut down during dynamic power-down, a power
savings of anywhere between 35% to 70% power can be achieved when the PDN_CYCLE phase is active.
The sequence of the convert phases within a pulse repetition period should be as follows: LED2 (Red) →
Ambient 2 → LED1 (IR) → Ambient 1. The sample phases must precede the corresponding convert phase. Also
note that the ADC_RDY signal comes at the beginning of the pulse repetition period. Thus, the contents of the
registers must be read before the completion of the first conversion phase in the pulse repetition period. These
contents correspond to the samples of the four phases from the previous pulse repetition period.
The DYNAMIC1, DYNAMIC2, DYNAMIC3, and DYNAMIC4 bits determine which blocks are powered down
during the dynamic power-down state (when PDN_CYCLE is high). For maximum power saving, all four bits can
be set to 1. TI recommends setting t1 to greater than 100 µs and t2 to greater than 200 µs to ensure that the
blocks recover from power-down in time for the next cycle.
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The bit corresponding to the TIA power-down (DYNAMIC3) needs a bit more consideration. When the TIA is
powered down, the TIA no longer maintains the bias across the photodiode output. This loss of bias can cause
the photodiode output voltage to drift from the normal value. The recovery time constant associated with the
photodiode returning to a proper bias condition (when the TIA is powered back on) is approximately equal to 2 ×
CPD × RF, where CPD is the effective differential capacitance of the photodiode and RF is the TIA gain setting.
This consideration might result in a different choice for the value of t2.
8.4.2 Diagnostics
The device includes diagnostics to detect open or short conditions of the LED and photosensor, LED current
profile feedback, and cable on or off detection.
8.4.2.1 Photodiode-Side Fault Detection
Figure 68 shows the diagnostic for the photodiode-side fault detection.
Internal
TX_CTRL_SUP
10 kꢀ
10 kꢀ
1 kꢀ
Cable
Rx On/Off
INN
INP
To Rx Front-End
Rx On/Off
GND Wires
PD Wires
LED Wires
Legend for Cable
Figure 68. Photodiode Diagnostic
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8.4.2.2 Transmitter-Side Fault Detection
Figure 69 shows the diagnostic for the transmitter-side fault detection.
Internal
TX_CTRL_SUP
10 kꢀ
10 kꢀ
Cable
TXP
D
C
TXN
GND Wires
PD Wires
LED DAC
LED Wires
Legend for Cable
Figure 69. Transmitter Diagnostic
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8.4.2.3 Diagnostics Module
The diagnostics module, when enabled, checks for nine types of faults sequentially. The results of all faults are latched in 11 separate flags.
The status of all flags can also be read using the SPI interface. Table 5 details each fault and flag used. Note that the diagnostics module requires all
AFE blocks to be enabled in order to function reliably.
Table 5. Fault and Flag Diagnostics(1)
MODULE
SEQ.
FAULT
FLAG1
FLAG2
FLAG3
FLAG4
FLAG5
FLAG6
FLAG7
FLAG8
FLAG9
FLAG10
FLAG11
—
—
No fault
0
0
0
0
0
0
0
0
0
0
0
Rx INP cable shorted to LED
cable
1
2
3
1
Rx INN cable shorted to LED
cable
1
PD
Rx INP cable shorted to GND
cable
1
Rx INN cable shorted to GND
cable
4
5
6
1
PD open or shorted
1
1
Tx OUTM line shorted to
GND cable
1
Tx OUTP line shorted to
GND cable
7
1
LED
8
9
LED open or shorted
LED open or shorted
1
1
1
(1) Resistances below 10 kΩ are considered to be shorted.
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Figure 70 shows the timing for the diagnostic function.
DIAG_EN Register Bit = 1
Diagnostic State
Machine
Diagnostic State Machine
Diagnostic Starts
Diagnostic Ends
DIAG_END Pin
tWIDTH = Four 4-MHz
Clock Cycles
tDIAG
Figure 70. Diagnostic Timing Diagram
By default, the diagnostic function takes tDIAG = 16 ms to complete. After the diagnostics function completes, the
AFE4403 filter must be allowed time to settle. See the Electrical Characteristics for the filter settling time.
8.5 Programming
8.5.1 Serial Programming Interface
The SPI-compatible serial interface consists of four signals: SCLK (serial clock), SPISOMI (serial interface data
output), SPISIMO (serial interface data input), and SPISTE (serial interface enable).
The serial clock (SCLK) is the serial peripheral interface (SPI) serial clock. SCLK shifts in commands and shifts
out data from the device. SCLK features a Schmitt-triggered input and clocks data out on the SPISOMI. Data are
clocked in on the SPISIMO pin. Even though the input has hysteresis, TI recommends keeping SCLK as clean
as possible to prevent glitches from accidentally shifting the data. When the serial interface is idle, hold SCLK
low.
The SPI serial out master in (SPISOMI) pin is used with SCLK to clock out the AFE4403 data. The SPI serial in
master out (SPISIMO) pin is used with SCLK to clock in data to the AFE4403. The SPI serial interface enable
(SPISTE) pin enables the serial interface to clock data on the SPISIMO pin in to the device.
8.5.2 Reading and Writing Data
The device has a set of internal registers that can be accessed by the serial programming interface formed by
the SPISTE, SCLK, SPISIMO, and SPISOMI pins.
8.5.2.1 Writing Data
The SPI_READ register bit must be first set to 0 before writing to a register. When SPISTE is low:
•
•
•
Serially shifting bits into the device is enabled.
Serial data (on the SPISIMO pin) are latched at every SCLK rising edge.
The serial data are loaded into the register at every 32nd SCLK rising edge.
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Programming (continued)
In case the word length exceeds a multiple of 32 bits, the excess bits are ignored. Data can be loaded in
multiples of 32-bit words within a single active SPISTE pulse. The first eight bits form the register address and
the remaining 24 bits form the register data. Figure 71 shows an SPI timing diagram for a single write operation.
For multiple read and write cycles, refer to the Multiple Data Reads and Writes section.
SPISTE
SPISIMO
SCLK
A7
A6
A1
A0
D23 D22
D17 D16
D15 D14
D9
D8
D7
D6
D1
D0
'RQ¶WꢀFDUH, can be high or low.
Figure 71. AFE SPI Write Timing Diagram
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Programming (continued)
8.5.2.2 Reading Data
The SPI_READ register bit must be first set to 1 before reading from a register. The AFE4403 includes a mode
where the contents of the internal registers can be read back on the SPISOMI pin. This mode may be useful as a
diagnostic check to verify the serial interface communication between the external controller and the AFE. To
enable this mode, first set the SPI_READ register bit using the SPI write command, as described in the Writing
Data section. In the next command, specify the SPI register address with the desired content to be read. Within
the same SPI command sequence, the AFE outputs the contents of the specified register on the SPISOMI pin.
Figure 72 shows an SPI timing diagram for a single read operation. For multiple read and write cycles, refer to
the Multiple Data Reads and Writes section.
SPISTE
SPISIMO
SPISOMI
A7
A6
A1
A0
D23 D22
D17 D16
D15 D14
D9
D8
D7
D6
D1
D0
SCLK
'RQ¶WꢀFDUH, can be high or low.
(1) The SPI_READ register bit must be enabled before attempting a serial readout from the AFE.
(2) Specify the register address of the content that must be readback on bits A[7:0].
(3) The AFE outputs the contents of the specified register on the SPISOMI pin.
Figure 72. AFE SPI Read Timing Diagram
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8.5.2.3 Multiple Data Reads and Writes
The device includes functionality where multiple read and write operations can be performed during a single SPISTE event. To enable this functionality,
the first eight bits determine the register address to be written and the remaining 24 bits determine the register data. Perform two writes with the SPI read
bit enabled during the second write operation in order to prepare for the read operation, as described in the Writing Data section. In the next command,
specify the SPI register address with the desired content to be read. Within the same SPI command sequence, the AFE outputs the contents of the
specified register on the SPISOMI pin. This functionality is described in the Writing Data and Reading Data sections. Figure 73 shows a timing diagram
for the SPI multiple read and write operations.
SPISTE
First Write
Second Write(1, 2)
Read(3, 4)
Operation
SPISIMO
SPISOMI
A7
A0
D23
D16
D15
D8
D7
D0
A7
A0
D23
D16
D15
D8
D7
D0
A7
A0
D23
D16
D15
D8
D7
D0
SCLK
'RQ¶WꢀFDUH, can be high or low
(1) The SPI read register bit must be enabled before attempting a serial readout from the AFE.
(2) The second write operation must be configured for register 0 with data 000001h.
(3) Specify the register address whose contents must be read back on A[7:0].
(4) The AFE outputs the contents of the specified register on the SPISOMI pin.
Figure 73. Serial Multiple Read and Write Operations
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8.5.2.4 Register Initialization
After power-up, the internal registers must be initialized to the default values. This initialization can be done in
one of two ways:
•
•
Through a hardware reset by applying a low-going pulse on the RESET pin, or
By applying a software reset. Using the serial interface, set SW_RESET (bit D3 in register 00h) high. This
setting initializes the internal registers to the default values and then self-resets to 0. In this case, the RESET
pin is kept high (inactive).
8.5.2.5 AFE SPI Interface Design Considerations
Note that when the AFE4403 is deselected, the SPISOMI, CLKOUT, ADC_RDY, and DIAG_END digital output
pins do not enter a 3-state mode. This condition, therefore, must be taken into account when connecting multiple
devices to the SPI port and for power-management considerations. In order to avoid loading the SPI bus when
multiple devices are connected, the SOMI_TRI register bit must be to 1 whenever the AFE SPI is inactive. The
DIGOUT_TRISTATE register bit must be set to 1 to tri-state the ADC_RDY and DIAG_END pins. The
CLKOUT_TRI register bit must be set to 1 to put the CLKOUT buffer in tri-state mode.
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8.6 Register Maps
8.6.1 AFE Register Map
The AFE consists of a set of registers that can be used to configure it, such as receiver timings, I-V amplifier settings, transmit LED currents, and so forth.
The registers and their contents are listed in Table 6. These registers can be accessed using the AFE SPI interface.
Table 6. AFE Register Map
ADDRESS
REGISTER DATA
REGISTER
NAME
CONTROL(1)
Hex
Dec
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
CONTROL0
W
00
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LED2STC
LED2ENDC
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
10
11
12
13
14
15
16
17
18
19
1A
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LED2STC[15:0]
LED2ENDC[15:0]
2
LED2LEDSTC
LED2LEDENDC
ALED2STC
3
LED2LEDSTC[15:0]
LED2LEDENDC[15:0]
ALED2STC[15:0]
4
5
ALED2ENDC
6
ALED2ENDC[15:0]
LED1STC[15:0]
LED1STC
7
LED1ENDC
8
LED1ENDC[15:0]
LED1LEDSTC
LED1LEDENDC
ALED1STC
9
LED1LEDSTC[15:0]
LED1LEDENDC[15:0]
ALED1STC[15:0]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
ALED1ENDC
ALED1ENDC[15:0]
LED2CONVST[15:0]
LED2CONVEND[15:0]
ALED2CONVST[15:0]
ALED2CONVEND[15:0]
LED1CONVST[15:0]
LED1CONVEND[15:0]
ALED1CONVST[15:0]
ALED1CONVEND[15:0]
ADCRSTCT0[15:0]
ADCRENDCT0[15:0]
ADCRSTCT1[15:0]
ADCRENDCT1[15:0]
ADCRSTCT2[15:0]
ADCRENDCT2[15:0]
LED2CONVST
LED2CONVEND
ALED2CONVST
ALED2CONVEND
LED1CONVST
LED1CONVEND
ALED1CONVST
ALED1CONVEND
ADCRSTSTCT0
ADCRSTENDCT0
ADCRSTSTCT1
ADCRSTENDCT1
ADCRSTSTCT2
ADCRSTENDCT2
(1) R = read only, R/W = read or write, N/A = not available, and W = write only.
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Table 6. AFE Register Map (continued)
ADDRESS
REGISTER DATA
REGISTER
CONTROL(1)
Hex
1B
Dec
27
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTSTCT3
ADCRSTENDCT3
PRPCOUNT
R/W
R/W
R/W
ADCRSTCT3[15:0]
ADCRENDCT3[15:0]
PRPCT[15:0]
1C
1D
28
0
0
0
0
0
0
0
0
29
0
0
0
0
0
0
0
0
CONTROL1
SPARE1
R/W
N/A
1E
1F
30
31
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
NUMAV[7:0]
0
0
0
0
0
0
0
0
0
TIAGAIN
R/W
R/W
20
21
32
33
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
STG2GAIN1[2:0]
STG2GAIN2[2:0]
CF_LED1[4:0]
CF_LED[4:0]
RF_LED1[2:0]
TIA_AMB_GAIN
AMBDAC[3:0]
RF_LED[2:0]
LEDCNTRL
CONTROL2
R/W
R/W
22
23
34
35
0
0
0
0
0
0
0
0
0
0
LED1[7:0]
LED2[7:0]
0
0
0
0
0
0
0
SPARE2
SPARE3
N/A
N/A
N/A
N/A
N/A
R/W
R
24
25
26
27
28
29
2A
2B
2C
2D
2E
2F
36
37
38
39
40
41
42
43
44
45
46
47
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
0
X
X
0
0
0
SPARE4
RESERVED1
RESERVED2
ALARM
X
X
0
LED2VAL
LED2VAL[23:0]
ALED2VAL[23:0]
LED1VAL[23:0]
ALED1VAL[23:0]
ALED2VAL
LED1VAL
R
R
ALED1VAL
LED2-ALED2VAL
LED1-ALED1VAL
R
R
LED2-ALED2VAL[23:0]
LED1-ALED1VAL[23:0]
R
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Table 6. AFE Register Map (continued)
ADDRESS
REGISTER
REGISTER DATA
NAME
CONTROL(1)
Hex
Dec
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
DIAG
R
30
48
0
0
0
0
0
0
0
0
0
0
0
CONTROL3
R/W
31
49
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CLKDIV[2:0]
PDNCYCLESTC
R/W
R/W
32
33
50
51
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
PDNCYCLESTC[15:0]
PDNCYCLEENDC[15:0]
PDNCYCLEENDC
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8.6.2 AFE Register Description
Figure 74. CONTROL0: Control Register 0 (Address = 00h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
11
10
9
8
7
6
5
4
3
2
1
0
TIM_
SPI_
READ
0
0
0
0
0
0
0
0
SW_RST DIAG_EN COUNT_
RST
This register is write-only. CONTROL0 is used for AFE software and count timer reset, diagnostics enable, and
SPI read functions.
Bits 23:4
Bit 3
Must be 0
SW_RST: Software reset
0 = No action (default after reset)
1 = Software reset applied; resets all internal registers to the default values and self-clears
to 0
Bit 2
DIAG_EN: Diagnostic enable
0 = No action (default after reset)
1 = Diagnostic mode is enabled and the diagnostics sequence starts when this bit is set.
At the end of the sequence, all fault status are stored in the DIAG: Diagnostics Flag
Register. Afterwards, the DIAG_EN register bit self-clears to 0.
Note that the diagnostics enable bit is automatically reset after the diagnostics completes
(16 ms). During the diagnostics mode, ADC data are invalid because of the toggling
diagnostics switches.
Bit 1
Bit 0
TIM_CNT_RST: Timer counter reset
0 = Disables timer counter reset, required for normal timer operation (default after reset)
1 = Timer counters are in reset state
SPI READ: SPI read
0 = SPI read is disabled (default after reset)
1 = SPI read is enabled
Figure 75. LED2STC: Sample LED2 Start Count Register (Address = 01h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
LED2STC[15:0]
11
10
9
8
7
6
5
4
3
2
1
LED2STC[15:0]
This register sets the start timing value for the LED2 signal sample.
Bits 23:16
Bits 15:0
Must be 0
LED2STC[15:0]: Sample LED2 start count
The contents of this register can be used to position the start of the sample LED2 signal with
respect to the pulse repetition period (PRP), as specified in the PRPCOUNT register. The
count is specified as the number of
4-MHz clock cycles. Refer to the Using the Timer Module section for details.
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Figure 76. LED2ENDC: Sample LED2 End Count Register (Address = 02h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED2ENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED2ENDC[15:0]
This register sets the end timing value for the LED2 signal sample.
Bits 23:16
Bits 15:0
Must be 0
LED2ENDC[15:0]: Sample LED2 end count
The contents of this register can be used to position the end of the sample LED2 signal with
respect to the PRP, as specified in the PRPCOUNT register. The count is specified as the
number of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
Figure 77. LED2LEDSTC: LED2 LED Start Count Register (Address = 03h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED2LEDSTC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED2LEDSTC[15:0]
This register sets the start timing value for when the LED2 signal turns on.
Bits 23:16
Bits 15:0
Must be 0
LED2LEDSTC[15:0]: LED2 start count
The contents of this register can be used to position the start of the LED2 with respect to the
PRP, as specified in the PRPCOUNT register. The count is specified as the number of 4-
MHz clock cycles. Refer to the Using the Timer Module section for details.
Figure 78. LED2LEDENDC: LED2 LED End Count Register (Address = 04h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED2LEDENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED2LEDENDC[15:0]
This register sets the end timing value for when the LED2 signal turns off.
Bits 23:16
Bits 15:0
Must be 0
LED2LEDENDC[15:0]: LED2 end count
The contents of this register can be used to position the end of the LED2 signal with respect
to the PRP, as specified in the PRPCOUNT register. The count is specified as the number
of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
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Figure 79. ALED2STC: Sample Ambient LED2 Start Count Register (Address = 05h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ALED2STC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ALED2STC[15:0]
This register sets the start timing value for the ambient LED2 signal sample.
Bits 23:16
Bits 15:0
Must be 0
ALED2STC[15:0]: Sample ambient LED2 start count
The contents of this register can be used to position the start of the sample ambient LED2
signal with respect to the PRP, as specified in the PRPCOUNT register. The count is
specified as the number of 4-MHz clock cycles. Refer to the Using the Timer Module section
for details.
Figure 80. ALED2ENDC: Sample Ambient LED2 End Count Register
(Address = 06h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
ALED2ENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
ALED2ENDC[15:0]
This register sets the end timing value for the ambient LED2 signal sample.
Bits 23:16
Bits 15:0
Must be 0
ALED2ENDC[15:0]: Sample ambient LED2 end count
The contents of this register can be used to position the end of the sample ambient LED2
signal with respect to the PRP, as specified in the PRPCOUNT register. The count is
specified as the number of 4-MHz clock cycles. Refer to the Using the Timer Module section
for details.
Figure 81. LED1STC: Sample LED1 Start Count Register (Address = 07h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
LED1STC[15:0]
11
10
9
8
7
6
5
4
3
2
1
LED1STC[15:0]
This register sets the start timing value for the LED1 signal sample.
Bits 23:17
Bits 16:0
Must be 0
LED1STC[15:0]: Sample LED1 start count
The contents of this register can be used to position the start of the sample LED1 signal with
respect to the PRP, as specified in the PRPCOUNT register. The count is specified as the
number of
4-MHz clock cycles. Refer to the Using the Timer Module section for details.
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Figure 82. LED1ENDC: Sample LED1 End Count (Address = 08h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
LED1ENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
LED1ENDC[15:0]
This register sets the end timing value for the LED1 signal sample.
Bits 23:17
Bits 16:0
Must be 0
LED1ENDC[15:0]: Sample LED1 end count
The contents of this register can be used to position the end of the sample LED1 signal with
respect to the PRP, as specified in the PRPCOUNT register. The count is specified as the
number of
4-MHz clock cycles. Refer to the Using the Timer Module section for details.
Figure 83. LED1LEDSTC: LED1 LED Start Count Register (Address = 09h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED1LEDSTC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED1LEDSTC[15:0]
This register sets the start timing value for when the LED1 signal turns on.
Bits 23:16
Bits 15:0
Must be 0
LED1LEDSTC[15:0]: LED1 start count
The contents of this register can be used to position the start of the LED1 signal with respect
to the PRP, as specified in the PRPCOUNT register. The count is specified as the number
of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
Figure 84. LED1LEDENDC: LED1 LED End Count Register (Address = 0Ah, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED1LEDENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED1LEDENDC[15:0]
This register sets the end timing value for when the LED1 signal turns off.
Bits 23:16
Bits 15:0
Must be 0
LED1LEDENDC[15:0]: LED1 end count
The contents of this register can be used to position the end of the LED1 signal with respect
to the PRP, as specified in the PRPCOUNT register. The count is specified as the number
of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
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Figure 85. ALED1STC: Sample Ambient LED1 Start Count Register (Address = 0Bh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ALED1STC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ALED1STC[15:0]
This register sets the start timing value for the ambient LED1 signal sample.
Bits 23:16
Bits 15:0
Must be 0
ALED1STC[15:0]: Sample ambient LED1 start count
The contents of this register can be used to position the start of the sample ambient LED1
signal with respect to the PRP, as specified in the PRPCOUNT register. The count is
specified as the number of 4-MHz clock cycles. Refer to the Using the Timer Module section
for details.
Figure 86. ALED1ENDC: Sample Ambient LED1 End Count Register
(Address = 0Ch, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
ALED1ENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
ALED1ENDC[15:0]
This register sets the end timing value for the ambient LED1 signal sample.
Bits 23:16
Bits 15:0
Must be 0
ALED1ENDC[15:0]: Sample ambient LED1 end count
The contents of this register can be used to position the end of the sample ambient LED1
signal with respect to the PRP, as specified in the PRPCOUNT register. The count is
specified as the number of 4-MHz clock cycles. Refer to the Using the Timer Module section
for details.
Figure 87. LED2CONVST: LED2 Convert Start Count Register (Address = 0Dh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED2CONVST[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED2CONVST[15:0]
This register sets the start timing value for the LED2 conversion.
Bits 23:16
Bits 15:0
Must be 0
LED2CONVST[15:0]: LED2 convert start count
The contents of this register can be used to position the start of the LED2 conversion signal
with respect to the PRP, as specified in the PRPCOUNT register. The count is specified as
the number of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
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Figure 88. LED2CONVEND: LED2 Convert End Count Register (Address = 0Eh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED2CONVEND[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED2CONVEND[15:0]
This register sets the end timing value for the LED2 conversion.
Bits 23:16
Bits 15:0
Must be 0
LED2CONVEND[15:0]: LED2 convert end count
The contents of this register can be used to position the end of the LED2 conversion signal
with respect to the PRP, as specified in the PRPCOUNT register. The count is specified as
the number of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
Figure 89. ALED2CONVST: LED2 Ambient Convert Start Count Register
(Address = 0Fh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
ALED2CONVST[15:0]
11
10
9
8
7
6
5
4
3
2
1
ALED2CONVST[15:0]
This register sets the start timing value for the ambient LED2 conversion.
Bits 23:16
Bits 15:0
Must be 0
ALED2CONVST[15:0]: LED2 ambient convert start count
The contents of this register can be used to position the start of the LED2 ambient
conversion signal with respect to the PRP, as specified in the PRPCOUNT register. The
count is specified as the number of 4-MHz clock cycles. Refer to the Using the Timer
Module section for details.
Figure 90. ALED2CONVEND: LED2 Ambient Convert End Count Register
(Address = 10h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
ALED2CONVEND[15:0]
11
10
9
8
7
6
5
4
3
2
1
ALED2CONVEND[15:0]
This register sets the end timing value for the ambient LED2 conversion.
Bits 23:16
Bits 15:0
Must be 0
ALED2CONVEND[15:0]: LED2 ambient convert end count
The contents of this register can be used to position the end of the LED2 ambient
conversion signal with respect to the PRP. The count is specified as the number of 4-MHz
clock cycles. Refer to the Using the Timer Module section for details.
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Figure 91. LED1CONVST: LED1 Convert Start Count Register (Address = 11h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED1CONVST[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED1CONVST[15:0]
This register sets the start timing value for the LED1 conversion.
Bits 23:16
Bits 15:0
Must be 0
LED1CONVST[15:0]: LED1 convert start count
The contents of this register can be used to position the start of the LED1 conversion signal
with respect to the PRP, as specified in the PRPCOUNT register. The count is specified as
the number of 4-MHz clock cycles. Refer to the Using the Timer Module section for details.
Figure 92. LED1CONVEND: LED1 Convert End Count Register (Address = 12h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
LED1CONVEND[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED1CONVEND[15:0]
This register sets the end timing value for the LED1 conversion.
Bits 23:16
Bits 15:0
Must be 0
LED1CONVEND[15:0]: LED1 convert end count
The contents of this register can be used to position the end of the LED1 conversion signal
with respect to the PRP. The count is specified as the number of 4-MHz clock cycles. Refer
to the Using the Timer Module section for details.
Figure 93. ALED1CONVST: LED1 Ambient Convert Start Count Register
(Address = 13h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
ALED1CONVST[15:0]
11
10
9
8
7
6
5
4
3
2
1
ALED1CONVST[15:0]
This register sets the start timing value for the ambient LED1 conversion.
Bits 23:16
Bits 15:0
Must be 0
ALED1CONVST[15:0]: LED1 ambient convert start count
The contents of this register can be used to position the start of the LED1 ambient
conversion signal with respect to the PRP, as specified in the PRPCOUNT register. The
count is specified as the number of 4-MHz clock cycles. Refer to the Using the Timer
Module section for details.
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Figure 94. ALED1CONVEND: LED1 Ambient Convert End Count Register
(Address = 14h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
ALED1CONVEND[15:0]
11
10
9
8
7
6
5
4
3
2
1
ALED1CONVEND[15:0]
This register sets the end timing value for the ambient LED1 conversion.
Bits 23:16
Bits 15:0
Must be 0
ALED1CONVEND[15:0]: LED1 ambient convert end count
The contents of this register can be used to position the end of the LED1 ambient
conversion signal with respect to the PRP. The count is specified as the number of 4-MHz
clock cycles. Refer to the Using the Timer Module section for details.
Figure 95. ADCRSTSTCT0: ADC Reset 0 Start Count Register (Address = 15h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTSTCT0[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTSTCT0[15:0]
This register sets the start position of the ADC0 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTSTCT0[15:0]: ADC RESET 0 start count
The contents of this register can be used to position the start of the ADC reset conversion
signal (default value after reset is 0000h). Refer to the Using the Timer Module section for
details.
Figure 96. ADCRSTENDCT0: ADC Reset 0 End Count Register (Address = 16h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTENDCT0[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTENDCT0[15:0]
This register sets the end position of the ADC0 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTENDCT0[15:0]: ADC RESET 0 end count
The contents of this register can be used to position the end of the ADC reset conversion
signal (default value after reset is 0000h). Refer to the Using the Timer Module section for
details.
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Figure 97. ADCRSTSTCT1: ADC Reset 1 Start Count Register (Address = 17h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTSTCT1[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTSTCT1[15:0]
This register sets the start position of the ADC1 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTSTCT1[15:0]: ADC RESET 1 start count
The contents of this register can be used to position the start of the ADC reset conversion.
Refer to the Using the Timer Module section for details.
Figure 98. ADCRSTENDCT1: ADC Reset 1 End Count Register (Address = 18h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTENDCT1[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTENDCT1[15:0]
This register sets the end position of the ADC1 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTENDCT1[15:0]: ADC RESET 1 end count
The contents of this register can be used to position the end of the ADC reset conversion.
Refer to the Using the Timer Module section for details.
Figure 99. ADCRSTSTCT2: ADC Reset 2 Start Count Register (Address = 19h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTSTCT2[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTSTCT2[15:0]
This register sets the start position of the ADC2 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTSTCT2[15:0]: ADC RESET 2 start count
The contents of this register can be used to position the start of the ADC reset conversion.
Refer to the Using the Timer Module section for details.
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Figure 100. ADCRSTENDCT2: ADC Reset 2 End Count Register (Address = 1Ah, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTENDCT2[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTENDCT2[15:0]
This register sets the end position of the ADC2 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTENDCT2[15:0]: ADC RESET 2 end count
The contents of this register can be used to position the end of the ADC reset conversion.
Refer to the Using the Timer Module section for details.
Figure 101. ADCRSTSTCT3: ADC Reset 3 Start Count Register (Address = 1Bh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTSTCT3[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTSTCT3[15:0]
This register sets the start position of the ADC3 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTSTCT3[15:0]: ADC RESET 3 start count
The contents of this register can be used to position the start of the ADC reset conversion.
Refer to the Using the Timer Module section for details.
Figure 102. ADCRSTENDCT3: ADC Reset 3 End Count Register (Address = 1Ch, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
ADCRSTENDCT3[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
ADCRSTENDCT3[15:0]
This register sets the end position of the ADC3 reset conversion signal.
Bits 23:16
Bits 15:0
Must be 0
ADCRSTENDCT3[15:0]: ADC RESET 3 end count
The contents of this register can be used to position the end of the ADC reset conversion
signal (default value after reset is 0000h). Refer to the Using the Timer Module section for
details.
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Figure 103. PRPCOUNT: Pulse Repetition Period Count Register (Address = 1Dh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
PRPCOUNT[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
PRPCOUNT[15:0]
This register sets the device pulse repetition period count.
Bits 23:16
Bits 15:0
Must be 0
PRPCOUNT[15:0]: Pulse repetition period count
The contents of this register can be used to set the pulse repetition period (in number of
clock cycles of the 4-MHz clock). The PRPCOUNT value must be set in the range of 800 to
64000. Values below 800 do not allow sufficient sample time for the four samples; see the
Electrical Characteristics table.
Figure 104. CONTROL1: Control Register 1 (Address = 1Eh, Reset Value = 0000h)
23
0
22
0
21
0
20
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
0
8
11
0
10
0
9
7
6
5
4
3
2
1
0
0
TIMEREN
NUMAV[7:0]
This register configures the clock alarm pin and timer.
Bits 23:9
Bit 8
Must be 0
TIMEREN: Timer enable
0 = Timer module is disabled and all internal clocks are off (default after reset)
1 = Timer module is enabled
Bits 7:0
NUMAV[7:0]: Number of averages
Specify an 8-bit value corresponding to the number of ADC samples to be averaged – 1.
For example, to average four ADC samples, set NUMAV[7:0] equal to 3.
The maximum number of averages is 16. Any setting of NUMAV[7:0] greater than or equal
to a decimal value of 15 results in the number of averages getting set to 16.
Figure 105. SPARE1: SPARE1 Register For Future Use (Address = 1Fh, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
11
0
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
This register is a spare register and is reserved for future use.
Bits 23:0 Must be 0
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Figure 106. TIAGAIN: Transimpedance Amplifier Gain Setting Register
(Address = 20h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
0
12
0
ENSEP
GAIN
STAGE2
EN1
11
0
10
9
8
7
6
5
4
3
2
1
0
STG2GAIN1[2:0]
CF_LED1[4:0]
RF_LED1[2:0]
This register sets the device transimpedance amplifier gain mode and feedback resistor and capacitor values.
Bits 23:16
Bit 15
Must be 0
ENSEPGAIN: Enable separate gain mode
0 = The RF, CF values and stage 2 gain settings are the same for both the LED2 and LED1
signals; the values are specified by the bits (RF_LED2, CF_LED2, STAGE2EN2,
STG2GAIN2) in the TIA_AMB_GAIN register (default after reset)
1 = The RF, CF values and stage 2 gain settings can be independently set for the LED2 and
LED1 signals. The values for LED1 are specified using the bits (RF_LED1, CF_LED1,
STAGE2EN1, STG2GAIN1) in the TIAGAIN register, whereas the values for LED2 are
specified using the corresponding bits in the TIA_AMB_GAIN register.
Bit 14
STAGE2EN1: Enable stage 2 for LED 1
0 = Stage 2 is bypassed (default after reset)
1 = Stage 2 is enabled with the gain value specified by the STG2GAIN1[2:0] bits
Bits 13:11
Bits 10:8
Must be 0
STG2GAIN1[2:0]: Program stage 2 gain for LED1
000 = 0 dB, or linear gain of 1 (default after
reset)
100 = 12 dB, or linear gain of 4
101 = Do not use
001 = 3.5 dB, or linear gain of 1.5
010 = 6 dB, or linear gain of 2
011 = 9.5 dB, or linear gain of 3
110 = Do not use
111 = Do not use
Bits 7:3
Bits 2:0
CF_LED1[4:0]: Program CF for LED1
00000 = 5 pF (default after reset)
00001 = 5 pF + 5 pF
00010 = 15 pF + 5 pF
00100 = 25 pF + 5 pF
01000 = 50 pF + 5 pF
10000 = 150 pF + 5 pF
Note that any combination of these CF settings is also supported by setting multiple bits to 1.
For example, to obtain CF = 100 pF, set bits 7:3 = 01111.
RF_LED1[2:0]: Program RF for LED1
000 = 500 kΩ (default after reset)
001 = 250 kΩ
010 = 100 kΩ
100 = 25 kΩ
101 = 10 kΩ
110 = 1 MΩ
111 = None
011 = 50 kΩ
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Figure 107. TIA_AMB_GAIN: Transimpedance Amplifier and Ambient Cancellation Stage Gain Register
(Address = 21h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
18
17
16
15
14
13
0
12
0
FLTR
CNRSEL
STAGE2
EN2
AMBDAC[3:0]
11
0
10
9
8
7
6
5
4
3
2
1
0
STG2GAIN[2:0]
CF_LED2[4:0]
RF_LED2[2:0]
This register configures the ambient light cancellation amplifier gain, cancellation current, and filter corner
frequency.
Bits 23:20
Bits 19:16
Must be 0
AMBDAC[3:0]: Ambient DAC value
These bits set the value of the cancellation current.
0000 = 0 µA (default after reset)
0001 = 1 µA
1000 = 8 µA
1001 = 9 µA
0010 = 2 µA
1010 = 10 µA
0011 = 3 µA
0100 = 4 µA
0101 = 5 µA
0110 = 6 µA
1011 = Do not use
1100 = Do not use
1101 = Do not use
1110 = Do not use
1111 = Do not use
0111 = 7 µA
Bit 15
Bit 14
Must be 0
STAGE2EN2: Stage 2 enable for LED 2
0 = Stage 2 is bypassed (default after reset)
1 = Stage 2 is enabled with the gain value specified by the STG2GAIN2[2:0] bits
Bits 13:11
Bits 10:8
Must be 0
STG2GAIN2[2:0]: Stage 2 gain setting for LED 2
000 = 0 dB, or linear gain of 1 (default after reset)
001 = 3.5 dB, or linear gain of 1.5
010 = 6 dB, or linear gain of 2
011 = 9.5 dB, or linear gain of 3
100 = 12 dB, or linear gain of 4
101 = Do not use
110 = Do not use
111 = Do not use
Bits 7:3
Bits 2:0
CF_LED[4:0]: Program CF for LEDs
00000 = 5 pF (default after reset)
00001 = 5 pF + 5 pF
00010 = 15 pF + 5 pF
00100 = 25 pF + 5 pF
01000 = 50 pF + 5 pF
10000 = 150 pF + 5 pF
Note that any combination of these CF settings is also supported by setting multiple bits to 1.
For example, to obtain CF = 100 pF, set D[7:3] = 01111.
RF_LED[2:0]: Program RF for LEDs
000 = 500 kΩ
001 = 250 kΩ
010 = 100 kΩ
011 = 50 kΩ
100 = 25 kΩ
101 = 10 kΩ
110 = 1 MΩ
111 = None
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Figure 108. LEDCNTRL: LED Control Register (Address = 22h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
16
15
14
13
12
0
LED_RANGE[1:0]
LED1[7:0]
11
10
9
8
7
6
5
4
3
2
1
LED1[7:0]
LED2[7:0]
This register sets the LED current range and the LED1 and LED2 drive current.
Bits 23:18
Bits 17:16
Must be 0
LED_RANGE[1:0]: LED range
These bits program the full-scale LED current range for Tx. Table 7 details the settings.
Bits 15:8
LED1[7:0]: Program LED current for LED1 signal
Use these register bits to specify the LED current setting for LED1 (default after reset is
00h).
The nominal value of the LED current is given by Equation 7, where the full-scale LED
current is either 0 mA or 50 mA (as specified by the LED_RANGE[1:0] register bits).
Bits 7:0
LED2[7:0]: Program LED current for LED2 signal
Use these register bits to specify the LED current setting for LED2 (default after reset is
00h).
The nominal value of LED current is given by Equation 8, where the full-scale LED current is
either 0 mA or 50 mA (as specified by the LED_RANGE[1:0] register bits).
Table 7. Full-Scale LED Current across Tx Reference Voltage Settings(1)
TX_REF = 0.25 V
TX_REF = 0.5 V
TX_REF = 0.75 V
TX_REF = 1.0 V
LED_RANGE[1:
0]
(2)
IMAX
VHR
IMAX
VHR
IMAX
VHR
IMAX
VHR
00 (default after
reset)
50 mA
0.75 V
100 mA
1.1 V
Do not use
—
Do not use
—
01
10
11
25 mA
50 mA
0.7 V
0.75 V
—
50 mA
100 mA
Tx is off
1.0 V
1.1 V
—
75 mA
Do not use
Tx is off
1.3 V
—
100 mA
Do not use
Tx is off
1.6 V
—
Tx is off
—
—
(1) For a 3-V to 3.6-V supply, use TX_REF = 0.25 or 0.5 V. For a 4.75-V to 5.25-V supply, use TX_REF = 0.75 V or 1.0 V.
(2) VHR refers to the headroom voltage (over and above the LED forward voltage and cable voltage drop) needed on the LED_DRV_SUP.
The VHR values specified are for the H-bridge configuration. In the common anode configuration, VHR can be lower by 0.25 V.
LED1[7:0]
´ Full-Scale Current
256
(7)
LED2[7:0]
´ Full-Scale Current
256
(8)
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Figure 109. CONTROL2: Control Register 2 (Address = 23h, Reset Value = 0000h)
23
0
22
0
21
0
20
19
0
18
17
16
0
15
0
14
13
0
12
0
DYNAMI
C1
DYNAMI
C2
TX_REF1 TX_REF0
11
10
9
8
7
6
0
5
0
4
3
2
1
0
DIGOUT_
TRI
STATE
EN_
SLOW_
DIAG
TXBRG
MOD
XTAL
DIS
DYNAMI DYNAMI
C3 C4
0
PDNTX
PDNRX PDNAFE
This register controls the LED transmitter, crystal, and the AFE, transmitter, and receiver power modes.
Bits 23:21
Bit 20
Must be 0
DYNAMIC1
0 = Transmitter is not powered down during dynamic power-down phase
1 = Transmitter is powered down during dynamic power-down phase
Bit 19
Must be 0
Bits 18:17
TX_REF[1:0]: Tx reference voltage
These bits set the transmitter reference voltage. This Tx reference voltage is available on
the device TX_REF pin.
00 = 0.25-V Tx reference voltage (default value after reset)
01 = 0.5-V Tx reference voltage
10 = 1.0-V Tx reference voltage
11 = 0.75-V Tx reference voltage, D3
Bits 16:15
Bit 14
Must be 0
DYNAMIC2
0 = Part of the ADC is not powered down during dynamic power-down phase
1 = Part of the ADC is powered down during dynamic power-down phase
Bit 11
Bit 10
Bit 9
TXBRGMOD: Tx bridge mode
0 = LED driver is configured as an H-bridge (default after reset)
1 = LED driver is configured as a push-pull
DIGOUT_TRISTATE: Tri-state bit for the ADC_RDY and DIAG_END pins
0 = ADC_RDY and DIAG_END are not tri-stated
1 = ADC_RDY and DIAG_END are tri-stated
XTALDIS: Crystal disable mode
0 = The crystal module is enabled; the 8-MHz crystal must be connected to the XIN and
XOUT pins
1 = The crystal module is disabled; an external 8-MHz clock must be applied to the XIN pin
Bit 8
EN_SLOW_DIAG: Fast diagnostics mode enable
0 = Fast diagnostics mode, 8 ms (default value after reset)
1 = Slow diagnostics mode, 16 ms
Bits 7:5
Bit 4
Must be 0
DYNAMIC3
0 = TIA is not powered down during dynamic power-down phase
1 = TIA is powered down during dynamic power-down phase
Bit 3
DYNAMIC4
0 = The rest of the ADC is not powered down during dynamic power-down phase
1 = The rest of the ADC is powered down during dynamic power-down phase
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Bit 2
Bit 1
Bit 0
PDN_TX: Tx power-down
0 = The Tx is powered up (default after reset)
1 = Only the Tx module is powered down
PDN_RX: Rx power-down
0 = The Rx is powered up (default after reset)
1 = Only the Rx module is powered down
PDN_AFE: AFE power-down
0 = The AFE is powered up (default after reset)
1 = The entire AFE is powered down (including the Tx, Rx, and diagnostics blocks)
Figure 110. SPARE2: SPARE2 Register For Future Use (Address = 24h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
11
0
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
This register is a spare register and is reserved for future use.
Bits 23:0 Must be 0
Figure 111. SPARE3: SPARE3 Register For Future Use (Address = 25h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
11
0
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
This register is a spare register and is reserved for future use.
Bits 23:0 Must be 0
Figure 112. SPARE4: SPARE4 Register For Future Use (Address = 26h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
11
0
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
This register is a spare register and is reserved for future use.
Bits 23:0
Must be 0
Figure 113. RESERVED1: RESERVED1 Register For Factory Use Only
(Address = 27h, Reset Value = XXXXh)
23
X(1)
11
X
22
X
21
X
20
X
19
X
18
X
17
X
16
X
15
X
14
X
13
X
12
X
10
X
9
8
7
6
5
4
3
2
1
0
X
X
X
X
X
X
X
X
X
X
(1) X = don't care.
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This register is reserved for factory use. Readback values vary between devices.
Figure 114. RESERVED2: RESERVED2 Register For Factory Use Only
(Address = 28h, Reset Value = XXXXh)
23
X(1)
11
X
22
X
21
X
20
X
19
X
18
X
17
X
16
X
15
X
14
X
13
X
12
X
10
X
9
8
7
6
5
4
3
2
1
0
X
X
X
X
X
X
X
X
X
X
(1) X = don't care.
This register is reserved for factory use. Readback values vary between devices.
Figure 115. ALARM: Alarm Register (Address = 29h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
0
11
0
10
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
This register controls the alarm pin functionality.
Bits 23:0 Must be 0
Figure 116. LED2VAL: LED2 Digital Sample Value Register (Address = 2Ah, Reset Value = 0000h)
23
22
21
20
19
18
17
16
15
14
13
12
LED2VAL[23:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED2VAL[23:0]
Bits 23:0
LED2VAL[23:0]: LED2 digital value
This register contains the digital value of the latest LED2 sample converted by the ADC. The
ADC_RDY signal goes high each time that the contents of this register are updated. The
host processor must readout this register before the next sample is converted by the AFE.
Figure 117. ALED2VAL: Ambient LED2 Digital Sample Value Register
(Address = 2Bh, Reset Value = 0000h)
23
11
22
10
21
20
19
18
17
16
15
14
13
1
12
0
ALED2VAL[23:0]
9
8
7
6
5
4
3
2
ALED2VAL[23:0]
Bits 23:0
ALED2VAL[23:0]: LED2 ambient digital value
This register contains the digital value of the latest LED2 ambient sample converted by the
ADC. The ADC_RDY signal goes high each time that the contents of this register are
updated. The host processor must readout this register before the next sample is converted
by the AFE.
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Figure 118. LED1VAL: LED1 Digital Sample Value Register (Address = 2Ch, Reset Value = 0000h)
23
22
21
20
19
18
17
16
15
14
13
12
LED1VAL[23:0]
11
10
9
8
7
6
5
4
3
2
1
0
LED1VAL[23:0]
Bits 23:0
LED1VAL[23:0]: LED1 digital value
This register contains the digital value of the latest LED1 sample converted by the ADC. The
ADC_RDY signal goes high each time that the contents of this register are updated. The
host processor must readout this register before the next sample is converted by the AFE.
Figure 119. ALED1VAL: Ambient LED1 Digital Sample Value Register
(Address = 2Dh, Reset Value = 0000h)
23
11
22
10
21
20
19
18
17
16
15
14
13
1
12
0
ALED1VAL[23:0]
9
8
7
6
5
4
3
2
ALED1VAL[23:0]
Bits 23:0
ALED1VAL[23:0]: LED1 ambient digital value
This register contains the digital value of the latest LED1 ambient sample converted by the
ADC. The ADC_RDY signal goes high each time that the contents of this register are
updated. The host processor must readout this register before the next sample is converted
by the AFE.
Figure 120. LED2-ALED2VAL: LED2-Ambient LED2 Digital Sample Value Register
(Address = 2Eh, Reset Value = 0000h)
23
11
22
21
20
19
18
17
16
15
14
13
12
0
LED2-ALED2VAL[23:0]
10
9
8
7
6
5
4
3
2
1
LED2-ALED2VAL[23:0]
Bits 23:0
LED2-ALED2VAL[23:0]: (LED2 – LED2 ambient) digital value
This register contains the digital value of the LED2 sample after the LED2 ambient is
subtracted. The host processor must readout this register before the next sample is
converted by the AFE.
Note that this value is inverted when compared to waveforms shown in many publications.
Figure 121. LED1-ALED1VAL: LED1-Ambient LED1 Digital Sample Value Register
(Address = 2Fh, Reset Value = 0000h)
23
11
22
21
20
19
18
17
16
15
14
13
12
0
LED1-ALED1VAL[23:0]
10
9
8
7
6
5
4
3
2
1
LED1-ALED1VAL[23:0]
Bits 23:0
LED1-ALED1VAL[23:0]: (LED1 – LED1 ambient) digital value
This register contains the digital value of the LED1 sample after the LED1 ambient is
subtracted from it. The host processor must readout this register before the next sample is
converted by the AFE.
Note that this value is inverted when compared to waveforms shown in many publications.
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Figure 122. DIAG: Diagnostics Flag Register (Address = 30h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
0
14
0
13
0
12
PD_ALM
0
11
10
9
8
7
6
5
4
3
2
1
LED_
ALM
LED2
OPEN
LED1
OPEN
OUTNSH OUTPSH
GND GND
INNSC
GND
INPSC
GND
INNSC
LED
INPSC
LED
LEDSC
PDOC
PDSC
This register is read only. This register contains the status of all diagnostic flags at the end of the diagnostics
sequence. The end of the diagnostics sequence is indicated by the signal going high on DIAG_END pin.
Bits 23:13
Bit 12
Read only
PD_ALM: Power-down alarm status diagnostic flag
This bit indicates the status of PD_ALM .
0 = No fault (default after reset)
1 = Fault present
Bit 11
Bit 10
Bit 9
LED_ALM: LED alarm status diagnostic flag
This bit indicates the status of LED_ALM .
0 = No fault (default after reset)
1 = Fault present
LED2OPEN: LED2 open diagnostic flag
This bit indicates that LED2 is open.
0 = No fault (default after reset)
1 = Fault present
LED1OPEN: LED1 open diagnostic flag
This bit indicates that LED1 is open.
0 = No fault (default after reset)
1 = Fault present
This bit indicates that LED2 is open.
0 = No fault (default after reset)
1 = Fault present
Bit 8
Bit 7
Bit 6
Bit 5
LEDSC: LED short diagnostic flag
This bit indicates an LED short.
0 = No fault (default after reset)
1 = Fault present
OUTNSHGND: OUTN to GND diagnostic flag
This bit indicates that OUTN is shorted to the GND cable.
0 = No fault (default after reset)
1 = Fault present
OUTPSHGND: OUTP to GND diagnostic flag
This bit indicates that OUTP is shorted to the GND cable.
0 = No fault (default after reset)
1 = Fault present
PDOC: PD open diagnostic flag
This bit indicates that PD is open.
0 = No fault (default after reset)
1 = Fault present
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Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
PDSC: PD short diagnostic flag
This bit indicates a PD short.
0 = No fault (default after reset)
1 = Fault present
INNSCGND: INN to GND diagnostic flag
This bit indicates a short from the INN pin to the GND cable.
0 = No fault (default after reset)
1 = Fault present
INPSCGND: INP to GND diagnostic flag
This bit indicates a short from the INP pin to the GND cable.
0 = No fault (default after reset)
1 = Fault present
INNSCLED: INN to LED diagnostic flag
This bit indicates a short from the INN pin to the LED cable.
0 = No fault (default after reset)
1 = Fault present
INPSCLED: INP to LED diagnostic flag
This bit indicates a short from the INP pin to the LED cable.
0 = No fault (default after reset)
1 = Fault present
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Figure 123. CONTROL3: Control Register (Address = 31h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
0
13
12
0
TX3_MO
DE
0
11
0
10
0
9
8
7
6
5
4
3
2
1
0
SOMI_
TRI
CLKOUT
_TRI
0
0
0
0
0
CLKDIV[2:0]
This register controls the clock divider ratio.
Bits 23:16
Bit 15
Must be 0
TX3_MODE: Selection of third LED
This bit transitions the control from the default two LEDs (on TXP, TXN) to the third LED on
TX3.
0 = LEDs on TXP, TXN are active
1 = LED on TX3 is active. Timing engine controls on TXP are transferred to TX3. Maximum
current setting supported for the third LED is 50 mA.
Bits 14:5
Bit 4
Must be 0
SOMI_TRI: Serial data output 3-state mode
This bit determines the state of the SPISOMI output pin. In order to avoid loading the SPI
bus when multiple devices are connected, this bit must be set to 1 (3-state mode) whenever
the device SPI is inactive.
0 = SPISOMI output buffer is active (normal operation, default)
1 = SPISOMI output buffer is in 3-state mode
Bit 3
CLKOUT_TRI: CLKOUT output 3-state mode
This bit determines the state of the CLKOUT output pin.
0 = CLKOUT buffer is active (normal operation, default)
1 = CLKOUT buffer is in 3-state mode
Bits 2:0
CLKDIV[2:0]: Clock divider ratio
These bits set the ratio of the clock divider and determine the frequency of CLKOUT relative
to the input clock frequency.
Table 8 shows the clock divider ratio settings.
Table 8. Clock Divider Ratio Settings
CLKDIV[2:0]
000
DIVIDER RATIO
Divide-by-2
Do not use
INPUT CLOCK FREQUENCY RANGE
8 MHz to 12 MHz(1)
Do not use
001
010
Divide-by-4
Divide-by-6
Divide-by-8
Divide-by-12
Do not use
16 MHz to 24 MHz(1)
24 MHz to 36 MHz
32 MHz to 48 MHz
48 MHz to 60 MHz
Do not use
011
100
101
110
111
Divide by 1(2)
4 MHz to 6 MHz
(1) These frequency ranges can be used when generating the clock using the crystal.
(2) When using divide-by-1, the external clock should have a duty cycle between 48% to 52%.
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Figure 124. PDNCYCLESTC: PDNCYCLESTC Register (Address = 32h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
0
PDNCYCLESTC[15:0]
11
10
9
8
7
6
5
4
3
2
1
PDNCYCLESTC[15:0]
Bits 23:16
Bits 15:0
Must be 0
PDNCYCLESTC[15:0]: Dynamic (cycle-to-cycle) power-down start count
The contents of this register can be used to position the start of the PDN_CYCLE signal with
respect to the pulse repetition period (PRP). The count is specified as the number of cycles
of CLKOUT. If the dynamic power-down feature is not required, then do not program this
register.
Figure 125. PDNCYCLEENDC: PDNCYCLEENDC Register (Address = 33h, Reset Value = 0000h)
23
0
22
0
21
0
20
0
19
0
18
0
17
0
16
0
15
14
13
12
PDNCYCLEENDC[15:0]
11
10
9
8
7
6
5
4
3
2
1
0
PDNCYCLEENDC[15:0]
Bits 23:16
Bits 15:0
Must be 0
PDNCYCLEENDC[15:0]: Dynamic (cycle-to-cycle) power-down end count
The contents of this register can be used to position the end of the PDN_CYCLE signal with
respect to the pulse repetition period (PRP). The count is specified as the number of cycles
of CLKOUT. If the dynamic power-down feature is not required, then do not program this
register.
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9 Application and Implementation
9.1 Application Information
The AFE4403 is ideally suited as an analog front-end for processing PPG (photoplethysmography) signals. The
information contained in PPG signals can be used for measuring SPO2 as well as for monitoring heart rate. The
high dynamic range of the device enables measuring SPO2 with a high degree of accuracy, even under
conditions of low perfusion (ac:dc ratio). An SPO2 measurement system involves two different wavelength LEDs:
usually Red and IR. By computing the ratio of the ac:dc at the two different wavelengths, SPO2 can be
calculated. Heart rate monitoring systems can also benefit from the high dynamic range of the AFE4403, which
enables a high-fidelity pulsating signal to be captured, even in cases where the signal strength is low.
9.2 Typical Application
Device connections in a typical application is shown in Figure 126. The schematic shows a cabled application in
which the LEDs and photodiode are connected to the device through a cable. However, in an application without
cables, the LEDs and photodiode can be directly connected to the TXP, TXN, TX3, INP, and INN pins directly.
Figure 126. Schematic
9.2.1 Design Requirements
An SPO2 application usually involves a Red LED and IR LED. In addition, a heart rate monitoring application can
use a different wavelength LED, such as a Green LED. The LEDs can be connected either in the common anode
configuration or H-bridge configuration to the TXP, TXN pins. The LED connected to the TX3 pin can only be
connected in the common anode configuration.
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Typical Application (continued)
9.2.2 Detailed Design Procedure
Refer to LED Configurations for different ways to connect the LEDs to the TXP, TXN, and TX3 pins. The
photodiode (shown in Figure 127) receives light from both the Red and IR phases and usually has good
sensitivities at both these wavelengths.
Figure 127. Photodiode
The photodiode connected as shown in Figure 127 operates in zero bias because of the negative feedback from
the transimpedance amplifier. The signal current generated by the photodiode is converted into a voltage by the
transimpedance amplifier, which has a programmable transimpedance gain. The rest of the signal chain then
presents a voltage to the ADC. The full-scale output of the transimpedance amplifier is ±1 V and the full-scale
input to the ADC is ±1.2 V. An automatic gain control (AGC) loop can be used to set the target dc voltage at the
ADC input to approximately 50% of its full-scale. Such an AGC loop can control a combination of the LED current
and TIA gain to achieve this target value.
9.2.3 Application Curves
This section outlines the trends seen in the Typical Characteristics curves from an application perspective.
Figure 5 illustrates the receiver currents in external clock mode with CLKOUT tri-stated. The curve in Figure 5
are taken without the dynamic power-down feature enabled, so much lower currents can be achieved using the
dynamic power-down feature. Enabling the crystal mode or removing the CLKOUT tri-state increases the
receiver currents from the values depicted in the curve.
Figure 6 illustrates the transmitter currents with a zero LED current setting. The average LED current can be
computed based on the value of the PRF and LED pulse durations, and can be added to the LED_DRV_SUP
current described in Figure 6.
Figure 7 illustrates the total receiver current (analog plus digital supply) for different clock divider ratios. For each
clock divider ratio, the external clock frequency is swept in frequency such that the divided clock changes
between 3 MHz to 7 MHz. Note however that the supported range for the divided clock is 4 MHz to 6 MHz at
each division ratio. Also, the external clock should be limited to be between 4 MHz to 60 MHz.
Figure 8 illustrates the power savings arising out of the dynamic power-down mode. This mode can be set by
defining the start and end points for the signal PDN_CYCLE within the pulse repetition period. In Figure 8, the
LED pulse durations are chosen to be 100 µs and the conversions are also chosen to be 100 µs wide. Thus, the
entire active period fits in 500 µs. With the timing margins for t1 and t2 indicated in Figure 67, the PDN_CYCLE
pulse spans the rest of the pulse repetition period. As PRF reduces, the duty cycle of the PDN_CYCLE pulse (as
a fraction of the pulse repetition period) increases, which is the reason for the power reduction at lower PRFs as
seen in Figure 8.
Figure 9 illustrates the power savings as a function of the PDN_CYCLE duration at a fixed PRF of 100 Hz. A
100-Hz PRF corresponds to a period of 10 ms. Figure 9 indicates the PDN_CYCLE duration swept from 0 ms to
9 ms. With higher durations of PDN_CYCLE, the receiver power reduces.
Figure 10 illustrates the baseband response of the switched RC filter for a 5% and 25% duty cycle. When the
duty cycle reduces, the effective bandwidth of the filter reduces.
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Typical Application (continued)
Figure 128 shows the SNR of the signal chain as a function of the output voltage level. The data are taken by
looping back the transmitter outputs to the receiver inputs using an external op amp that converts the transmitter
voltage to a receiver input current. The loopback op amp and external resistors are an extra source of noise in
this measurement, so the actual noise levels are higher than the total noise of the transmitter plus the receiver.
The SNR in this curve (and other curves) is expressed in terms of dBFS, where the full-scale of the channel is
used as the reference level. Because the valid operating range of the signal chain is ±1 V, a full-scale of 2 V is
used for converting the output noise to a dBFS number. %FS refers to the percentage of the output level as a
function of the positive full-scale. For example, a 50 %FS curve corresponds to the case where the output level is
0.5 V. Also, the total noise in this curve is the total integrated noise in the digital output. All noise is contained in
the Nyquist band, which extends from –PRF / 2 to PRF / 2.
106
Output voltage = 0 %FS
Output voltage = 10 %FS
104
Output voltage = 25 %FS
Output voltage = 50 %FS
102
100
98
Output voltage = 75 %FS
96
0
5
10
15
20
25
Duty Cycle (%)
C007
Figure 128. SNR over Nyquist Bandwidth vs Duty Cycle (Input Current with Tx-Rx Loopback)
Figure 129 is a representation of the same data as Figure 10. However, the noise is represented in terms of the
input-referred noise current in pArms. By multiplying this number with the TIA gain setting (500 k in this case),
the output noise voltage can be computed.
50
Output voltage = 0 %FS
45
Output voltage = 10 %FS
Output voltage = 25 %FS
Output voltage = 50 %FS
Output voltage = 75 %FS
40
35
30
25
20
15
10
0
5
10
15
20
25
Duty Cycle (%)
C006
Figure 129. Input-Referred Noise Current over Nyquist Bandwidth vs Duty Cycle
(Input Current with Tx-Rx Loopback)
Figure 13 illustrates the SNR from the receiver as a function of the sampling duty cycle (which is the sampling
pulse duration referred to the pulse repetition period) for different settings of TIA gain. This curve is taken at 100-
Hz PRF. The maximum duty cycle is limited to 25%. A lower sampling duty cycle also means a lower LED pulse
duration duty cycle, which results in power saving.
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Typical Application (continued)
Figure 14 illustrates the input-referred noise corresponding to Figure 13. Figure 15 and Figure 16 illustrate the
SNR and input-referred noise current in a 0.1-Hz to 20-Hz band for the LED-ambient data. By performing a
digital ambient subtraction, the low-frequency noise in the signal chain can be significantly attenuated. The noise
levels in the bandwidth of interest are lower than the noise over the full Nyquist bandwidth. For a PPG signal, the
signal band of interest is usually less than 10 Hz. By performing some digital low-pass filtering in the processor,
this noise reduction can be achieved. Figure 17 and Figure 18 illustrate the noise reduction from ADC averaging.
TI therefore recommends setting the number of ADC averages to the maximum allowed at a given PRF.
Figure 19 and Figure 20 illustrate the noise at different PRFs over a 20-Hz bandwidth. At a higher PRF, the 20-
Hz noise band is a smaller fraction of the Nyquist band. Thus, noise is lower at higher PRFs in these figures.
Figure 21 and Figure 22 illustrate the noise at different PRFs over a 20-Hz bandwidth with dynamic power-down
mode enabled. The active window remains as 500 µs and all samples and conversions are performed at this
time. For the rest of the period, the device is in dynamic power-down with the t1 and t2 values as described in
Figure 67. Again, the noise reduces with higher PRF. Figure 23 and Figure 24 illustrate the noise as a function of
the PDN_CYCLE duration varied from 0 ms to 9 ms, with the active duration (available for conversion) occupying
the rest of the period. With higher PDN_CYCLE durations, the number of allowed ADC averages reduces, ehich
explains the slight increase in noise at higher PDN_CYCLE durations. Figure 25 and Figure 26 illustrate the
noise as a function of temperature over a 20-Hz bandwidth. The measurements are performed with a transmit-
receive loopback as explained earlier. The input current is maintained at 1 µA. Thus, for 250-k gain setting, the
output voltage is 0.5 V and for a 500-k gain setting, the output voltage is 1 V. Figure 27 and Figure 28 illustrate
the noise reduction using additional gain in stage 2. Figure 29 shows the noise as a function of the internal
(divided) clock frequency. The external clock is varied from 7 MHz to 14 MHz with a clock division ratio of 2. This
range of external clock results in the internal clock varying from 3.5 MHz to 7 MHz. Out of this range, 4 MHz to 6
MHz is the allowed range for the internal (divided) clock at all clock division ratios. Figure 30 illustrates the
deviation in the measured LED current with respect to the calculated current when the LED current code is swept
from 0 to 255 in steps of 1.
Figure 31 and Figure 32 illustrate the transmitter+receiver noise (in external loopback mode) as a function of the
TX_REF voltage setting. At lower TX_REF voltages, there is a slight increase in the transmitter noise. This
increase is not very apparent from the curves because the transmitter noise is at a level much lower than the
total noise. Figure 33 illustrates the transmitter current as a function of the current setting code. Figure 34
illustrates the spread of the transmitter current taken across a large number of devices for the same current
setting. Figure 35 illustrates how the LED current changes linearly with the TX_REF voltage for a fixed code.
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10 Power Supply Recommendations
The AFE4403 has two sets of supplies: the receiver supplies (RX_ANA_SUP, RX_DIG_SUP) and the transmitter
supplies (TX_CTRL_SUP, LED_DRV_SUP). The receiver supplies can be between 2.0 V to 3.6 V, whereas the
transmitter supplies can be between 3.0 V to 5.25 V. Another consideration that determines the minimum allowed
value of the transmitter supplies is the forward voltage of the LEDs being driven. The current source and
switches inside the AFE require voltage headroom that mandates the transmitter supply to be a few hundred
millivolts higher than the LED forward voltage. TX_REF is the voltage that governs the generation of the LED
current from the internal reference voltage. Choosing the lowest allowed TX_REF setting reduces the additional
headroom required but results in higher transmitter noise. Other than for the highest-end clinical SPO2
applications, this extra noise resulting from a lower TX_REF setting can be acceptable.
Consider a design where the LEDs are meant to be used in common anode configuration with a current setting
of 50 mA. Assume that the LED manufacturer mentions the highest forward voltage of the LEDs is 2.5 V at this
current setting. Further, assume that the TX_REF voltage is set to 0.5 V. The voltage headroom required in this
case is 1 V. Thus, the LED_DRV_SUP must be driven with a voltage level greater than or equal to 3.5 V (2.5 V
plus 1 V).
LED_DRV_SUP and TX_CTRL_SUP are recommended to be tied together to the same supply (between 3.0 V to
5.25 V). The external supply (connected to the common anode of the two LEDs) must be high enough to account
for the forward drop of the LEDs as well as the voltage headroom required by the current source and switches
inside the AFE. In most cases, this voltage is expected to fall below 5.25 V; thus the external supply can be the
same as LED_DRV_SUP. However, there may be cases (for instance when two LEDs are connected in series)
where the voltage required on the external supply is higher than 5.25 V. Such a case must be handled with care
to ensure that the voltage on the TXP and TXN pins remains less than 5.25 V and never exceeds the supply
voltage of LED_DRV_SUP, TX_CTRL_SUP by more than 0.3 V.
Many scenarios of power management are possible.
Case 1: The LED forward voltage is such that a voltage of 3.3 V is acceptable on LED_DRV_SUP. In this case,
a single 3.3-V supply can be used to drive all four pins (RX_ANA_SUP, RX_DIG_SUP, TX_CTRL_SUP,
LED_DRV_SUP). Care should be taken to provide some isolation between the transmit and receive supplies
because LED_DRV_SUP carries the high-switching current from the LEDs.
Case 2: A low-voltage supply of 2.2 V is available in the system. In this case, a boost converter can be used to
derive the voltage for LED_DRV_SUP, as shown in Figure 130.
2.2-V supply
(Connect to RX_ANA, RX_DIG)
3.6 V
(Connect to LED_DRV_SUP, TX_CTRL_SUP)
Boost
Converter
Figure 130. Boost Converter
The boost converter requires a clock (usually in the megahertz range) and there is usually a ripple at the boost
converter output at this switching frequency. While this frequency is much higher than the signal frequency of
interest (which is at maximum a few tens of hertz around dc), a small fraction of this switching noise can possibly
alias to the low-frequency band. Therefore, TI strongly recommends that the switching frequency of the boost
converter be offset from every multiple of the PRF by at least 20 Hz. This offset can be ensured by choosing the
appropriate PRF.
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Case 3: In cases where a high-voltage supply is available in the system, a buck converter or an LDO can be
used to derive the voltage levels required to drive RX_ANA and RX_DIG, as shown in Figure 131.
3.9V
(Connect to LED_DRV_SUP, TX_CTRL_SUP)
2.2V supply
(Connect to RX_ANA/RX_DIG)
LDO
Figure 131. Buck Converter or an LDO
10.1 Power Consumption Considerations
The lowest power consumption mode of the AFE4403 corresponds to the following settings:
•
•
•
PRF = 62.5 Hz,
External clock mode (XTALDIS = 1), and
CLKOUT tri-stated (CLKOUT_TRI = 1).
With the above settings, the currents taken from the supplies are as shown in Table 9. The LED driver current is
with zero LED current setting.
Table 9. Current Consumption in Normal Mode
SUPPLY
RX_ANA
VOLTAGE (V)
CURRENT (µA)
2
2
3
3
490
155
15
RX_DIG
TX_CTRL_SUP
LED_DRV_SUP
55
Enabling the crystal (XTALDIS = 0) leads to an additional power consumption that can be estimated to be
approximately equal to (2 × Csh + 0.5 × C1 + 0.5 × C2) × 0.4 × fXTAL, where Csh is the effective shunt capacitance
of the crystal, C1 and C2 are the capacitances from the XIN and XOUT pins to ground, and fXTAL is the frequency
of the crystal.
Removing the CLKOUT tri-state leads to an additional power consumption of approximately CLOAD × VSUP × f,
where VSUP is the supply voltage of RX_DIG in volts, f = 4 MHz, CLOAD = the capacitive load on the CLKOUT pin
+ 2 pF.
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The power consumption can be reduced significantly by using the dynamic power-down mode. An illustration of
this mode is shown in Table 10, where:
•
•
•
•
•
PRF = 62.5 Hz,
Dynamic power-down is active for 14.7 ms every pulse repetition period,
All four bits (DYNAMIC[4:1]) are set to 1,
External clock mode (XTALDIS = 1), and
CLKOUT is tri-stated (CLKOUT_TRI = 1).
Table 10. Current Consumption in Dynamic Power-Down Mode
SUPPLY
RX_ANA
VOLTAGE (V)
CURRENT (µA)
2
2
3
3
150
155
5
RX_DIG
TX_CTRL_SUP
LED_DRV_SUP
5
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11 Layout
11.1 Layout Guidelines
Some key layout guidelines are mentioned below:
1. TXP, TXN, and TX3 are fast-switching lines and should be routed away from sensitive reference lines as well
as from the INP, INN inputs.
2. If the INP, INN lines are required to be routed over a long trace, TI recommends that VCM be used as a
shield for the INP, INN lines.
3. The device can draw high-switching currents from the LED_DRV_SUP pin. Therefore, TI recommends
having a decoupling capacitor electrically close to the pin.
11.2 Layout Example
Figure 132. Example Layout
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12 Device and Documentation Support
12.1 Trademarks
SPI is a trademark of Motorola.
All other trademarks are the property of their respective owners.
12.2 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
12.3 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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2-Jul-2014
PACKAGING INFORMATION
Orderable Device
AFE4403YZPR
AFE4403YZPT
Status Package Type Package Pins Package
Eco Plan
Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
-20 to 70
Device Marking
Samples
Drawing
Qty
(1)
(2)
(6)
(3)
(4/5)
ACTIVE
DSBGA
DSBGA
YZP
36
36
3000
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
AFE4403
AFE4403
ACTIVE
YZP
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
-20 to 70
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
2-Jul-2014
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
17-Jun-2015
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
AFE4403YZPR
AFE4403YZPT
DSBGA
DSBGA
YZP
YZP
36
36
3000
250
180.0
180.0
8.4
8.4
3.16
3.16
3.16
3.16
0.71
0.71
4.0
4.0
8.0
8.0
Q1
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
17-Jun-2015
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
AFE4403YZPR
AFE4403YZPT
DSBGA
DSBGA
YZP
YZP
36
36
3000
250
182.0
182.0
182.0
182.0
20.0
20.0
Pack Materials-Page 2
D: Max = 3.07 mm, Min = 3.01 mm
E: Max = 3.07 mm, Min = 3.01 mm
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