AD7680_11 [ADI]
3 mW, 100 kSPS, 16-Bit ADC in 6-Lead SOT-23; 3毫瓦， 100 kSPS时， 16位ADC，采用6引脚SOT -23
| 型号： | AD7680_11 |
| 厂家： | 
ADI |
| 描述： | 3 mW, 100 kSPS, 16-Bit ADC in 6-Lead SOT-23 |
| 文件： | 总24页 (文件大小：301K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
3 mW, 100 kSPS,
16-Bit ADC in 6-Lead SOT-23
AD7680
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Fast throughput rate: 100 kSPS
Specified for VDD of 2.5 V to 5.5 V
Low power
3 mW typ at 100 kSPS with 2.5 V supply
3.9 mW typ at 100 kSPS with 3 V supply
16.7 mW typ at 100 kSPS with 5 V supply
Wide input bandwidth
86 dB SNR at 10 kHz input frequency
Flexible power/serial clock speed management
No pipeline delays
V
DD
16-BIT SUCCESSIVE
APPROXIMATION
ADC
V
T/H
IN
SCLK
SDATA
CS
CONTROL
LOGIC
AD7680
GND
High speed serial interface
SPI®/QSPI™/μWire/DSP compatible
Standby mode: 0.5 μA max
Figure 1.
6-Lead SOT-23 and 8-Lead MSOP packages
Table 1. MSOP/SOT-23 16-Bit PulSAR ADC
APPLICATIONS
Type/kSPS
100 kSPS
AD7684
AD7683
AD7680
250 kSPS
AD7687
AD7685
500 kSPS
AD7688
AD7686
True Differential
Pseudo Differential
Unipolar
Battery-powered systems:
Personal digital assistants
Medical instruments
Mobile communications
Instrumentation and control systems
Remote data acquisition systems
High speed modems
Optical sensors
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
1. First 16-bit ADC in a SOT-23 package.
The AD7680 is a 16-bit, fast, low power, successive
approximation ADC. The part operates from a single 2.5 V to
5.5 V power supply and features throughput rates up to 100 kSPS.
The part contains a low noise, wide bandwidth track-and-hold
amplifier that can handle input frequencies in excess of 7 MHz.
2. High throughput with low power consumption.
3. Flexible power/serial clock speed management. The
conversion rate is determined by the serial clock, allowing
the conversion time to be reduced through the serial clock
speed increase. This allows the average power consumption
to be reduced when a power-down mode is used while not
converting. The part also features a shutdown mode to
maximize power efficiency at lower throughput rates.
Power consumption is 0.5 μA max when in shutdown.
The conversion process and data acquisition are controlled
CS
using
with microprocessors or DSPs. The input signal is sampled on
CS
and the serial clock, allowing the devices to interface
the falling edge of
and the conversion is also initiated at this
point. There are no pipeline delays associated with the part.
4. Reference derived from the power supply.
5. No pipeline delays.
The AD7680 uses advanced design techniques to achieve very
low power dissipation at fast throughput rates. The reference for
the part is taken internally from VDD, which allows the widest
dynamic input range to the ADC. Thus, the analog input range
for this part is 0 V to VDD. The conversion rate is determined by
the SCLK frequency.
This part features a standard successive approximation ADC
with accurate control of the sampling instant via a
once-off conversion control.
CS
input and
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.326.8703© 2004-2011 Analog Devices, Inc. All rights reserved.
AD7680
TABLE OF CONTENTS
Specifications..................................................................................... 2
Typical Connection Diagram ................................................... 13
Digital Inputs.......................................................................... 13
Modes of Operation ....................................................................... 14
Normal Mode.............................................................................. 14
Power-Down Mode.................................................................... 15
Power vs. Throughput Rate........................................................... 16
Serial Interface ................................................................................ 17
AD7680 to ADSP-218x.............................................................. 18
Application Hints ........................................................................... 19
Grounding and Layout .............................................................. 19
Outline Dimensions....................................................................... 20
Ordering Guide .......................................................................... 21
Specifications..................................................................................... 4
Timing Specifications....................................................................... 6
Absolute Maximum Ratings............................................................ 7
ESD Caution.................................................................................. 7
Pin Configurations and Function Descriptions ........................... 8
Terminology ...................................................................................... 9
Typical Performance Characteristics ........................................... 10
Circuit Information........................................................................ 12
Converter Operation.................................................................. 12
Analog Input ............................................................................... 12
ADC Transfer Function................................................................. 13
REVISION HISTORY
5/11—Rev. 0 to Rev. A
Deleted the Evaluating the AD7680 Performance Section ...... 19
Changes to Ordering Guide .......................................................... 21
1/04—Revision 0: Initial Version
Rev. A | Page 2 of 24
AD7680
SPECIFICATIONS1
Table 2. VDD = 4.5 V to 5.5 V, fSCLK = 2.5 MHz, fSAMPLE = 100 kSPS, unless otherwise noted; TA = TMIN to TMAX, unless otherwise noted
Parameter
A, B Versions1
Unit
Test Conditions/Comments
DYNAMIC PERFORMANCE
Signal-to-Noise + Distortion (SINAD)2
fIN = 10 kHz sine wave
83
85
84
86
−97
−95
dB min
dB typ
dB min
dB typ
dB typ
dB typ
Signal-to-Noise Ratio (SNR)2
Total Harmonic Distortion (THD)2
Peak Harmonic or Spurious Noise (SFDR)2
Intermodulation Distortion (IMD)2
Second-Order Terms
Third-Order Terms
Aperture Delay
−94
−100
20
dB typ
dB typ
ns max
ps typ
Aperture Jitter
30
Full Power Bandwidth
8
2.2
MHz typ
MHz typ
@ −3 dB
@ −0.1 dB
DC ACCURACY
No Missing Codes
Integral Nonlinearity2
Offset Error2
15
4
1.68
0.038
Bits typ
LSB typ
mV max
% FS max
Gain Error2
ANALOG INPUT
Input Voltage Ranges
DC Leakage Current
Input Capacitance
LOGIC INPUTS
0 to VDD
0.3
30
V
μA max
pF typ
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
2.8
0.4
0.3
10
V min
V max
μA max
pF max
Typically 10 nA, VIN = 0 V or VDD
2, 3
Input Capacitance, CIN
LOGIC OUTPUTS
Output High Voltage, VOH
Output Low Voltage, VOL
Floating-State Leakage Current
Floating-State Output Capacitance2, 3
Output Coding
VDD − 0.2
0.4
0.3
V min
ISOURCE = 200 μA
ISINK = 200 μA
V max
μA max
pF max
10
Straight (Natural) Binary
CONVERSION RATE
Conversion Time
8
μs max
20 SCLK cycles with SCLK at 2.5 MHz
24 SCLK cycles with SCLK at 2.5 MHz
9.6
1.5
400
100
μs max
μs max
ns max
kSPS
Track-and-Hold Acquisition Time
Sine wave input ≤ 10 kHz
See the Serial Interface section
Throughput Rate
POWER REQUIREMENTS
VDD
4.5/5.5
V min/V max
IDD
Digital I/PS = 0 V or VDD
SCLK on or off. VDD = 5.5 V
fSAMPLE = 100 kSPS. VDD = 5.5 V; 3.3 mA typ
SCLK on or off. VDD = 5.5 V
VDD = 5.5 V
Normal Mode (Static)
Normal Mode (Operational)
Full Power-Down Mode
Power Dissipation4
Normal Mode (Operational)
Full Power-Down
5.2
4.8
0.5
mA max
mA max
μA max
26.4
2.75
mW max
μW max
fSAMPLE = 100 kSPS
1Temperature range as follows: B Version: −40°C to +85°C.
2 See the Terminology section.
3 Sample tested during initial release to ensure compliance.
4 See the Power vs. Throughput Rate section.
Rev. A | Page 3 of 24
AD7680
SPECIFICATIONS1
Table 3. VDD = 2.5 V to 4.096 V, fSCLK = 2.5 MHz, fSAMPLE = 100 kSPS, unless otherwise noted; TA = TMIN to TMAX, unless otherwise noted.
Parameter
A Version1
B Version1
Unit
Test Conditions/Comments
fIN = 10 kHz sine wave
VDD = 4.096 V
DYNAMIC PERFORMANCE
Signal-to-Noise + Distortion (SINAD)2
83
82
86
84
83
86
−98
−95
83
82
86
84
83
86
−98
−99
dB min
dB min
dB typ
dB min
dB min
dB typ
dB typ
dB typ
VDD = 2.5 V to 3.6 V
Signal-to-Noise Ratio (SNR)2
VDD = 4.096 V
VDD = 2.5 V to 3.6 V
Total Harmonic Distortion (THD)2
Peak Harmonic or Spurious Noise (SFDR)2
Intermodulation Distortion (IMD)2
Second-Order Terms
Third-Order Terms
Aperture Delay
−94
−100
20
30
7
5
2
1.6
−94
−100
10
30
7
5
2
1.6
dB typ
dB typ
ns max
ps typ
MHz typ
MHz typ
MHz typ
MHz typ
Aperture Jitter
Full Power Bandwidth
@ −3 dB; VDD = 4.096 V
@ −3 dB; VDD = 2.5 V to 3.6 V
@ −0.1 dB; VDD = 4.096 V
@ −0.1 dB; VDD = 2.5 V to 3.6 V
DC ACCURACY
No Missing Codes
Integral Nonlinearity2
14
3.5
3
1.25
1.098
0.038
15
3.5
3
1.25
1.098
0.038
Bits min
LSB max
LSB max
mV max
mV max
% FS max
VDD = 4.096 V
VDD = 2.5 V to 3.6 V
VDD = 4.096 V
Offset Error2
VDD = 2.5 V to 3.6 V
Gain Error2
ANALOG INPUT
Input Voltage Ranges
DC Leakage Current
Input Capacitance
LOGIC INPUTS
0 to VDD
0.3
30
0 to VDD
0.3
30
V
μA max
pF typ
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
2.4
0.4
0.3
10
2.4
0.4
0.3
10
V min
V max
μA max
pF max
Typically 10 nA, VIN = 0 V or VDD
2, 3
Input Capacitance, CIN
LOGIC OUTPUTS
Output High Voltage, VOH
Output Low Voltage, VOL
Floating-State Leakage Current
Floating-State Output Capacitance2, 3
Output Coding
VDD − 0.2
0.4
0.3
VDD − 0.2
0.4
0.3
V min
ISOURCE = 200 μA
ISINK = 200 μA
V max
μA max
pF max
10
10
Straight (Natural) Binary
CONVERSION RATE
Conversion Time
8
8
μs max
μs max
μs max
ns max
kSPS
20 SCLK cycles with SCLK at 2.5 MHz
24 SCLK cycles with SCLK at 2.5 MHz
Full-scale step input
Sine wave input ≤ 10 kHz
See the Serial Interface section
9.6
1.5
400
100
9.6
1.5
400
100
Track-and-Hold Acquisition Time
Throughput Rate
Rev. A | Page 4 of 24
AD7680
Parameter
A Version1
B Version1
Unit
Test Conditions/Comments
POWER REQUIREMENTS
VDD
2.5/4.096
2.5/4.096
V min/max
IDD
Digital I/Ps = 0 V or VDD
Normal Mode (Static)
2.8
2
2.6
1.9
0.3
2.8
2
2.6
1.9
0.3
mA max
mA max
mA max
mA max
μA max
SCLK on or off; VDD = 4.096 V
SCLK on or off; VDD = 3.6 V
fSAMPLE = 100 kSPS; VDD = 4.096 V; 1.75 mA typ
fSAMPLE = 100 kSPS; VDD = 3.6 V; 1.29 mA typ
SCLK on or off
Normal Mode (Operational)
Full Power-Down Mode
Power Dissipation4
Normal Mode (Operational)
10.65
6.84
3
1.23
1.08
10.65
6.84
3
1.23
1.08
mW max
mW max
mW typ
μW max
μW max
fSAMPLE = 100 kSPS; VDD = 4.096 V
fSAMPLE = 100 kSPS; VDD = 3.6 V
VDD = 2.5 V
VDD = 4.096V
VDD = 3.6 V
Full Power-Down
1 Temperature range as follows: A, B Versions: −40°C to +85°C.
2 See the Terminology section.
3 Sample tested during initial release to ensure compliance.
4 See the Power vs. Throughput Rate section.
Rev. A | Page 5 of 24
AD7680
TIMING SPECIFICATIONS1
Table 4. VDD = 2.5 V to 5.5 V; TA = TMIN to TMAX, unless otherwise noted.
Limit at TMIN, TMAX
Parameter
3 V
250
2.5
5 V
250
2.5
Unit
Description
2
fSCLK
kHz min
MHz max
tCONVERT
tQUIET
t1
20 × tSCLK 20 × tSCLK min
100
10
100
10
ns min
ns min
ns min
ns max
ns max
ns min
ns min
ns min
ns max
μs typ
Minimum quiet time required between bus relinquish and start of next conversion
CS
Minimum
pulse width
t2
10
10
CS
to SCLK setup time
3
t3
48
35
CS
Delay from until SDATA three-state disabled
Data access time after SCLK falling edge
SCLK low pulse width
3
t4
120
0.4 tSCLK
0.4 tSCLK
10
80
t5
t6
t7
0.4 tSCLK
0.4 tSCLK
10
SCLK high pulse width
SCLK to data valid hold time
SCLK falling edge to SDATA high impedance
Power up time from full power-down
4
t8
45
35
5
tPOWER-UP
1
1
1 Sample tested during initial release to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V.
2 Mark/space ratio for the SCLK input is 40/60 to 60/40.
3 Measured with the load circuit of Figure 2 and defined as the time required for the output to cross 0.8 V or 2.0 V.
4 t8 is derived form the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 2. The measured number is then extrapolated
back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t8, quoted in the timing characteristics is the true bus relinquish
time of the part and is independent of the bus loading.
5 See Power vs. Throughput Rate section.
200μA
I
OL
TO OUTPUT
PIN
1.6V
C
L
50pF
200μA
I
OH
Figure 2. Load Circuit for Digital Output Timing Specification
Rev. A | Page 6 of 24
AD7680
ABSOLUTE MAXIMUM RATINGS
Table 5. TA = 25°C, unless otherwise noted.
Stresses above those listed under Absolute Maximum Ratings
Parameter
Rating
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those listed in the operational sections
of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
VDD to GND
−0.3 V to +7 V
−0.3 V to VDD + 0.3 V
−0.3 V to +7 V
−0.3 V to VDD + 0.3 V
10 mA
Analog Input Voltage to GND
Digital Input Voltage to GND
Digital Output Voltage to GND
Input Current to Any Pin Except Supplies1
Operating Temperature Range
Commercial (B Version)
Storage Temperature Range
Junction Temperature
−40°C to +85°C
−65°C to +150°C
150°C
SOT-23 Package, Power Dissipation
θJA Thermal Impedance
θJC Thermal Impedance
MSOP Package, Power Dissipation
θJA Thermal Impedance
θJC Thermal Impedance
Lead Temperature, Soldering
Vapor Phase (60 secs)
450 mW
229.6°C/W
91.99°C/W
450 mW
205.9°C/W
43.74°C/W
215°C
220°C
2 kV
Infared (15 secs)
ESD
1Transient currents of up to 100 mA do not cause SCR latch-up.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the
human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. A | Page 7 of 24
AD7680
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
SOT-23
MSOP
V
1
2
3
6
5
4
CS
V
1
2
3
4
8
7
6
5
CS
DD
DD
AD7680
AD7680
GND
SDATA
SCLK
GND
GND
SDATA
NC
TOP VIEW
TOP VIEW
V
IN
(Not to Scale)
(Not to Scale)
V
SCLK
IN
Figure 3. SOT-23 Pin Configuration
NC = NO CONNECT
Figure 4. MSOP Pin Configuration
Table 6. Pin Function Descriptions
Pin No.
SOT-23
Pin No.
MSOP
Mnemonic Function
1
2
1
2, 3
VDD
GND
Power Supply Input. The VDD range for the AD7680 is from 2.5 V to 5.5 V.
Analog Ground. Ground reference point for all circuitry on the AD7680. All analog input signals should
be referred to this GND voltage.
3
4
4
5
VIN
SCLK
Analog Input. Single-ended analog input channel. The input range is 0 V to VDD.
Serial Clock. Logic input. SCLK provides the serial clock for accessing data from this part. This clock
input is also used as the clock source for the AD7680's conversion process.
5
7
SDATA
Data Out. Logic output. The conversion result from the AD7680 is provided on this output as a serial
data stream. The bits are clocked out on the falling edge of the SCLK input. The data stream from the
AD7680 consists of four leading zeros followed by 16 bits of conversion data that are provided MSB
CS
first. This will be followed by four trailing zeroes if is held low for a total of 24 SCLK cycles. See the
Serial Interface section.
6
8
6
CS
Chip Select. Active low logic input. This input provides the dual function of initiating conversions on
the AD7680 and framing the serial data transfer.
No Connect. This pin should be left unconnected.
N/A
NC
Rev. A | Page 8 of 24
AD7680
TERMINOLOGY
Integral Nonlinearity
Total Harmonic Distortion (THD)
This is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. The
endpoints of the transfer function are zero scale, a point
1/2 LSB below the first code transition, and full scale, a point
1/2 LSB above the last code transition.
THD is the ratio of the rms sum of harmonics to the
fundamental. For the AD7680, it is defined as
V2 2 +V32 +V4 2 +V5 2 +V6
2
THD(dB) = 20log
V1
where V1 is the rms amplitude of the fundamental and V2, V3,
V4, V5, and V6 are the rms amplitudes of the second through the
sixth harmonics.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Peak Harmonic or Spurious Noise
Offset Error
Peak harmonic or spurious noise is defined as the ratio of the
rms value of the next largest component in the ADC output
spectrum (up to fS/2, excluding dc) to the rms value of the
fundamental. Normally, the value of this specification is
determined by the largest harmonic in the spectrum, but for
ADCs where the harmonics are buried in the noise floor, it is a
noise peak.
This is the deviation of the first code transition (00 . . . 000) to
(00 . . . 001) from the ideal, i.e., AGND + 1 LSB.
Gain Error
This is the deviation of the last code transition (111 . . . 110) to
(111 . . . 111) from the ideal (i.e., VREF − 1 LSB) after the offset
error has been adjusted out.
Track-and-Hold Acquisition Time
Intermodulation Distortion
The track-and-hold amplifier returns to track mode at the end
of conversion. The track-and-hold acquisition time is the time
required for the output of the track-and-hold amplifier to reach
its final value, within 1 LSB, after the end of the conversion.
See the Serial Interface section for more details.
With inputs consisting of sine waves at two frequencies, fa and fb,
any active device with nonlinearities creates distortion products
at the sum and difference frequencies of mfa nfb where m, n =
0, 1, 2, 3. Intermodulation distortion terms are those for which
neither m nor n are equal to zero. For example, the second-order
terms include (fa + fb) and (fa − fb), while the third-order terms
include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa −2fb).
Signal-to-(Noise + Distortion) Ratio
This is the measured ratio of signal-to-(noise + distortion) at
the output of the ADC. The signal is the rms amplitude of the
fundamental. Noise is the sum of all nonfundamental signals up
to half the sampling frequency (fS/2, excluding dc). The ratio
depends on the number of quantization levels in the digitization
process; the more levels, the smaller the quantization noise. The
theoretical signal-to-(noise + distortion) ratio for an ideal N-bit
converter with a sine wave input is given by
The AD7680 is tested using the CCIF standard where two input
frequencies near the top end of the input bandwidth are used.
In this case, the second-order terms are usually distanced in
frequency from the original sine waves, while the third-order
terms are usually at a frequency close to the input frequencies.
As a result, the second- and third-order terms are specified
separately. The calculation of the intermodulation distortion is
as per the THD specification where it is the ratio of the rms
sum of the individual distortion products to the rms amplitude
of the sum of the fundamentals expressed in dBs.
Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB
Thus, for a 16-bit converter, this is 98 dB.
Rev. A | Page 9 of 24
AD7680
TYPICAL PERFORMANCE CHARACTERISTICS
Figure 5 shows a typical FFT plot for the AD7680 at 100 kSPS
sample rate and 10 kHz input frequency. Figure 6 shows the
signal-to-(noise + distortion) ratio performance versus the
input frequency for various supply voltages while sampling at
100 kSPS with an SCLK of 2.5 MHz.
Figure 7 shows a graph of the total harmonic distortion versus
the analog input frequency for various supply voltages, while
Figure 8 shows a graph of the total harmonic distortion versus
the analog input frequency for various source impedances (see
the Analog Input section). Figure 9 and Figure 10 show the
typical INL and DNL plots for the AD7680.
0
110
F
T
= 100kSPS
= 25°C
V
F
= 5V
SAMPLE
DD
= 100kSPS
A
SAMPLE
–20
–40
F
= 10kHz
IN
SNR = 88.28dB
SINAD = 87.82dB
THD = –97.76dB
SFDR = –98.25dB
105
100
95
V
V
V
V
V
V
V
= 4.3V
= 4.75V
= 3.6V
= 5.25V
= 3.0V
= 2.7V
= 2.5V
DD
DD
DD
DD
DD
DD
DD
–60
–80
–100
–120
–140
–160
90
10
0
10k
20k
30k
40k
50k
100
FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
Figure 5. AD7680 Dynamic Performance at 100 kSPS
Figure 7. AD7680 THD vs. Analog Input Frequency
for Various Supply Voltages at 100 kSPS
110
105
100
95
95
90
85
80
F
T
= 100kSPS
= 25°C
SAMPLE
R
= 10Ω
IN
A
R
= 50Ω
IN
V
= 5.25V
DD
R
= 100Ω
IN
90
V
V
V
V
V
= 4.75V
DD
DD
DD
DD
DD
= 4.3V
= 3.6V
= 3.0V
= 2.7V
85
F
T
V
= 100kSPS
SAMPLE
= 25°C
80
A
R
= 1000Ω
IN
= 4.75V
DD
75
10
V
= 2.5V
DD
100
10
100
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
Figure 8. AD7680 THD vs. Analog Input Frequency
for Various Source Impedances
Figure 6. AD7680 SINAD vs. Analog Input Frequency
for Various Supply Voltages at 100 kSPS
Rev. A | Page 10 of 24
AD7680
2.5
2.0
1.5
1.0
0.5
0
1.5
1.0
V
= 3.0V
DD
V
= 3.0V
DD
TEMP = 25°C
TEMP = 25°C
0.5
0
–0.5
–1.0
–1.5
–0.5
–1.0
0
10000
20000
30000
40000
50000
60000
70000
0
10000
20000
30000
40000
50000
60000
70000
CODE
CODE
Figure 9. AD7680 Typical INL
Figure 10. AD7680 Typical DNL
Rev. A | Page 11 of 24
AD7680
CIRCUIT INFORMATION
The AD7680 is a fast, low power, 16-bit, single-supply ADC. The
part can be operated from a 2.5 V to 5.5 V supply and is capable of
throughput rates of 100 kSPS when provided with a 2.5 MHz clock.
CAPACITIVE
DAC
SAMPLING
CAPACITOR
A
V
IN
SW1
CONTROL
LOGIC
B
The AD7680 provides the user with an on-chip track-and-hold
ADC and a serial interface housed in a tiny 6-lead SOT-23
package or in an 8-lead MSOP package, which offer the user
considerable space-saving advantages over alternative solutions.
The serial clock input accesses data from the part and also
provides the clock source for the successive approximation
ADC. The analog input range for the AD7680 is 0 V to VDD. An
external reference is not required for the ADC nor is there a
reference on-chip. The reference for the AD7680 is derived from
the power supply and thus gives the widest dynamic input range.
CONVERSION
PHASE
SW2
COMPARATOR
V
/2
DD
Figure 12. ADC Conversion Phase
ANALOG INPUT
Figure 13 shows an equivalent circuit of the analog input
structure of the AD7680. The two diodes, D1 and D2, provide
ESD protection for the analog inputs. Care must be taken to
ensure that the analog input signal never exceeds the supply
rails by more than 300 mV. This causes these diodes to become
forward-biased and to start conducting current into the
substrate. The maximum current these diodes can conduct
without causing irreversible damage to the part is 10 mA.
Capacitor C1 in Figure 13 is typically about 5 pF and can be
attributed primarily to pin capacitance. Resistor R1 is a lumped
component made up of the on resistance of a track-and-hold
switch. This resistor is typically about 25 Ω. Capacitor C2 is the
ADC sampling capacitor and has a capacitance of 25 pF
typically. For ac applications, removing high frequency
components from the analog input signal is recommended by
use of an RC low-pass filter on the relevant analog input pin. In
applications where harmonic distortion and signal-to-noise
ratio are critical, the analog input should be driven from a low
impedance source. Large source impedances significantly affect
the ac performance of the ADC. This may necessitate the use of
an input buffer amplifier. The choice of the op amp is a function
of the particular application. When no amplifier is used to drive
the analog input, the source impedance should be limited to low
values. The maximum source impedance depends on the
amount of total harmonic distortion (THD) that can be
tolerated. The THD increases as the source impedance
increases, and performance degrades (see Figure 8).
The AD7680 also features a power-down option to save power
between conversions. The power-down feature is implemented
across the standard serial interface as described in the Modes of
Operation section.
CONVERTER OPERATION
The AD7680 is a 16-bit, successive approximation ADC based
around a capacitive DAC. The AD7680 can convert analog
input signals in the 0 V to VDD range. Figure 11 and Figure 12
show simplified schematics of the ADC. The ADC comprises
control logic, SAR, and a capacitive DAC. Figure 11 shows the
ADC during its acquisition phase. SW2 is closed and SW1 is in
Position A. The comparator is held in a balanced condition and
the sampling capacitor acquires the signal on the selected VIN
channel.
CAPACITIVE
DAC
SAMPLING
A
CAPACITOR
V
IN
SW1
CONTROL
LOGIC
B
ACQUISITION
PHASE
SW2
COMPARATOR
V
/2
DD
Figure 11. ADC Acquisition Phase
V
DD
When the ADC starts a conversion, SW2 opens and SW1 moves
to Position B, causing the comparator to become unbalanced
(Figure 12). The control logic and the capacitive DAC are used
to add and subtract fixed amounts of charge from the sampling
capacitor to bring the comparator back into a balanced
condition. When the comparator is rebalanced, the conversion
is complete. The control logic generates the ADC output code
(see the ADC Transfer Function section).
C2
D1
25pF
R1
V
IN
C1
5pF
D2
CONVERSION PHASE - SWITCH OPEN
TRACK PHASE - SWITCH CLOSED
Figure 13. Equivalent Analog Input Circuit
Rev. A | Page 12 of 24
AD7680
ADC TRANSFER FUNCTION
The output coding of the AD7680 is straight binary. The
designed code transitions occur at successive integer LSB
values, i.e., 1 LSB, 2 LSBs. The LSB size is VDD/65536. The ideal
transfer characteristic for the AD7680 is shown in Figure 14.
In fact, because the supply current required by the AD7680 is so
low, a precision reference can be used as the supply source to
the AD7680. For example, a REF19x voltage reference (REF195
for 5 V or REF193 for 3 V) or an AD780 can be used to supply
the required voltage to the ADC (see Figure 15). This
configuration is especially useful if the power supply available is
quite noisy, or if the system supply voltages are at some value
other than the required operating voltage of the AD7680, e.g.,
15 V. The REF19x or AD780 outputs a steady voltage to the
AD7680. Recommended decoupling capacitors are a 100 nF low
ESR ceramic (Farnell 335-1816) and a 10 μF low ESR tantalum
(Farnell 197-130).
111...111
111...110
111...000
1 LSB = V /65536
DD
011...111
3V
5V
SUPPLY
REF193
10F
000...010
000...001
000...000
0.1F
10F
0.1F
TANT
1 LSB
+V –1 LSB
DD
V
DD
0V
SCLK
ANALOG INPUT
0V TO V
DD
V
IN
SDATA
CS
C/P
INPUT
AD7680
Figure 14. AD7680 Transfer Characteristic
GND
TYPICAL CONNECTION DIAGRAM
Figure 15 shows a typical connection diagram for the AD7680.
VREF is taken internally from VDD and as such should be well
decoupled. This provides an analog input range of 0 V to VDD.
The conversion result is output in a 24-bit word, or alternatively,
all 16 bits of the conversion result may be accessed using a
minimum of 20 SCLKs. This 20-/24-bit data stream consists of
a four leading zeros, followed by the 16 bits of conversion data,
followed by four trailing zeros in the case of the 24 SCLK
transfer. For applications where power consumption is of
concern, the power-down mode should be used between
conversions or bursts of several conversions to improve power
performance (see the Modes of Operation section).
SERIAL
INTERFACE
Figure 15. Typical Connection Diagram
Digital Inputs
The digital inputs applied to the AD7680 are not limited by the
maximum ratings that limit the analog inputs. Instead, the
digital inputs applied can go to 7 V and are not restricted by the
V
DD + 0.3 V limit as on the analog inputs. For example, if the
AD7680 were operated with a VDD of 3 V, 5 V logic levels could
be used on the digital inputs. However, it is important to note
that the data output on SDATA still has 3 V logic levels when
VDD = 3 V.
CS
Another advantage of SCLK and
not being restricted by the
VDD + 0.3 V limit is that power supply sequencing issues are
avoided. If one of these digital inputs is applied before VDD, then
there is no risk of latch-up as there would be on the analog
inputs if a signal greater than 0.3 V were applied prior to VDD.
Rev. A | Page 13 of 24
AD7680
MODES OF OPERATION
The mode of operation of the AD7680 is selected by controlling
CS
as described
The conversion is initiated on the falling edge of
in the Serial Interface section. To ensure that the part remains
CS
CS
the (logic) state of the
two possible modes of operation, normal and power-down. The
CS
signal during a conversion. There are
fully powered up at all times,
10 SCLK falling edges have elapsed after the falling edge of
CS
must remain low until at least
point at which
is pulled high after the conversion has been
CS
.
initiated determines whether or not the AD7680 enters power-
down mode. Similarly, if the AD7680 is already in power-down,
If
is brought high any time after the 10th SCLK falling edge,
but before the 20th SCLK falling edge, the part remains
powered up, but the conversion is terminated and SDATA goes
back into three-state. At least 20 serial clock cycles are required
to complete the conversion and access the complete conversion
result. In addition, a total of 24 SCLK cycles accesses four
CS
can control whether the device returns to normal operation
or remains in power-down. These modes of operation are
designed to provide flexible power management options. These
options can optimize the power dissipation/throughput rate
ratio for differing application requirements.
CS
trailing zeros.
may idle low until
conversion, effectively idling
may idle high until the next conversion or
CS
returns high sometime prior to the next
CS
NORMAL MODE
low.
This mode provides the fastest throughput rate performance,
because the user does not have to worry about the power-up
times with the AD7680 remaining fully powered all the time.
Figure 16 shows the general diagram of the operation of the
AD7680 in this mode.
Once a data transfer is complete (SDATA has returned to three-
state), another conversion can be initiated after the quiet time,
CS
tQUIET, has elapsed by bringing
low again.
CS
1
10
20
SCLK
4 LEADING ZEROS + CONVERSION RESULT
SDATA
Figure 16. Normal Mode Operation
Rev. A | Page 14 of 24
AD7680
POWER-DOWN MODE
This mode is intended for use in applications where slower
throughput rates are required. Either the ADC is powered
down between each conversion, or a series of conversions may
be performed at a high throughput rate, and then the ADC is
powered down for a relatively long duration between these
bursts of several conversions. When the AD7680 is in
power-down, all analog circuitry is powered down.
In order to exit this mode of operation and power up the
AD7680 again, a dummy conversion is performed. On the
CS
falling edge of , the device begins to power up and continues
CS
to power up as long as
is held low until after the falling edge
of the 10th SCLK. The device is fully powered up once at least
16 SCLKs (or approximately 6 μs) have elapsed and valid data
CS
results from the next conversion as shown in Figure 18. If
is
brought high before the 10th falling edge of SCLK, regardless of
the SCLK frequency, the AD7680 goes back into power-down
again. This avoids accidental power-up due to glitches on the
To enter power-down, the conversion process must be
CS
interrupted by bringing
falling edge of SCLK and before the 10th falling edge of SCLK
CS
high anywhere after the second
CS
CS
line or an inadvertent burst of 8 SCLK cycles while
So although the device may begin to power-up on the falling
is low.
as shown in Figure 17. Once
window of SCLKs, the part enters power-down, the conversion
CS
has been brought high in this
CS
CS
edge of , it powers down again on the rising edge of
as
that was initiated by the falling edge of
CS
is terminated, and
is brought high before
long as it occurs before the 10th SCLK falling edge.
SDATA goes back into three-state. If
the second SCLK falling edge, the part remains in normal mode
and will not power down. This avoids accidental power-down
CS
due to glitches on the
line.
CS
1
2
10
20
SCLK
THREE-STATE
SDATA
Figure 17. Entering Power-Down Mode
THE PART IS FULLY POWERED
UP WITH V FULLY ACQUIRED
IN
THE PART BEGINS
TO POWER UP
tPOWER UP
CS
1
10
20
1
20
SCLK
INVALID DATA
VALID DATA
SDATA
Figure 18. Exiting Power-Down Mode
Rev. A | Page 15 of 24
AD7680
POWER VS. THROUGHPUT RATE
By using the power-down mode on the AD7680 when not
converting, the average power consumption of the ADC
decreases at lower throughput rates. Figure 19 shows how as the
throughput rate is reduced, the part remains in its shut-down
state longer, and the average power consumption over time
drops accordingly.
Figure 19 shows the power dissipation versus the throughput
rate when using the power-down mode with 3.6 V supplies, a
2.5 MHz SCLK, and a 20 SCLK serial transfer.
10
V
= 3.6V
DD
F
= 2.5MHz
SCLK
For example, if the AD7680 is operated in a continuous
sampling mode, with a throughput rate of 10 kSPS and an SCLK
of 2.5 MHz (VDD = 3.6 V), and the device is placed in power-
down mode between conversions, the power consumption is
calculated as follows. The maximum power dissipation during
normal operation is 6.84 mW (VDD = 3.6 V). If the power-up
time from power-down is 1 μs, and the remaining conversion
time is 8 μs, (using a 20 SCLK transfer), then the AD7680 can
be said to dissipate 6.84 mW for 9 μs during each conversion
cycle. With a throughput rate of 10 kSPS, the cycle time is 100
μs.
1
0.1
0.01
0
5
10
15
20
25
30
35
40
45
50
THROUGHPUT (kSPS)
For the remainder of the conversion cycle, 91 μs, the part
remains in power-down mode. The AD7680 can be said to
dissipate 1.08 μW for the remaining 91 μs of the conversion
cycle. Therefore, with a throughput rate of 10 kSPS, the average
power dissipated during each cycle is
Figure 19. Power vs. Throughput Using
Power-Down Mode with 20 SCLK Transfer at 3.6 V
(9/100) × (6.84 mW) + (91/100) × (1.08 μW) = 0.62 mW
Rev. A | Page 16 of 24
AD7680
SERIAL INTERFACE
Figure 20 shows the detailed timing diagram for serial
interfacing to the AD7680. The serial clock provides the
conversion clock and also controls the transfer of information
from the AD7680 during conversion.
A minimum of 20 serial clock cycles are required to perform
the conversion process and to access data from the AD7680.
CS
going low provides the first leading zero to be read in by the
microcontroller or DSP. The remaining data is then clocked out
by subsequent SCLK falling edges beginning with the second
leading zero; thus the first falling clock edge on the serial clock
has the first leading zero provided and also clocks out the
second leading zero. If a 24 SCLK transfer is used as in Figure 20,
the data transfer consists of four leading zeros followed by the
16 bits of data, followed by four trailing zeros. The final bit
(fourth trailing zero) in the data transfer is valid on the 24th
falling edge, having been clocked out on the previous (23rd)
falling edge. If a 20 SCLK transfer is used as shown in Figure 21,
the data output stream consists of only four leading zeros
followed by 16 bits of data with the final bit valid on the 20th
SCLK falling edge. A 20 SCLK transfer allows for a shorter cycle
time and therefore a faster throughput rate is achieved.
CS
The
signal initiates the data transfer and conversion process.
CS
The falling edge of
puts the track-and-hold into hold mode,
takes the bus out of three-state, and samples the analog input.
The conversion is also initiated at this point and requires at least
20 SCLK cycles to complete. Once 17 SCLK falling edges have
elapsed, the track-and-hold goes back into track mode on the
next SCLK rising edge. Figure 20 shows a 24 SCLK transfer that
allows a 100 kSPS throughput rate. On the 24th SCLK falling
edge, the SDATA line goes back into three-state. If the rising
CS
edge of
occurs before 24 SCLKs have elapsed, the conversion
terminates and the SDATA line goes back into three-state;
otherwise SDATA returns to three-state on the 24th SCLK
falling edge as shown in Figure 20.
t1
CS
tCONVERT
t2
t6
1
2
3
4
5
18
19
20
21
22
23
24
t8
SCLK
t5
t7
t3
ZERO
t4
DB15
tQUIET
0
ZERO
ZERO
DB1
DB0
ZERO
ZERO
ZERO
ZERO
SDATA
3-STATE
3-STATE
4 LEADING ZEROS
4 TRAILING ZEROS
Figure 20. AD7680 Serial Interface Timing Diagram—24 SCLK Transfer
t1
CS
tCONVERT
t2
t6
1
2
3
4
5
18
19
20
SCLK
t5
t8
t7
DB1
t3
ZERO
t4
tQUIET
SDATA
0
ZERO
ZERO
DB15
DB0
0
3-STATE
3-STATE
4 LEADING ZEROS
Figure 21. AD7680 Serial Interface Timing Diagram—20 SCLK Transfer
Rev. A | Page 17 of 24
AD7680
It is also possible to take valid data on each SCLK rising edge
rather than falling edge, since the SCLK cycle time is long
enough to ensure the data is ready on the rising edge of SCLK.
an input. The DSP operates in alternate framing mode and the
SPORT control register is set up as described. Transmit and
receive autobuffering is used in order to get a 24 SCLK transfer.
Each buffer contains three 8-bit words. The frame synchroniza-
CS
However, the first leading zero is still driven by the
edge, and so it can be taken on only the first SCLK falling edge.
CS
falling
CS
tion signal generated on the TFS is tied to , and as with all
signal processing applications, equidistant sampling is necessary.
In this example, the timer interrupt is used to control the
sampling rate of the ADC.
It may be ignored and the first rising edge of SCLK after the
falling edge would have the second leading zero provided and
the 23rd rising SCLK edge would have the final trailing zero
provided. This method may not work with most
microcontrollers/DSPs but could possibly be used with FPGAs
and ASICs.
ADSP-218x*
SCLK
AD7680*
SCLK
SDATA
CS
DR
AD7680 TO ADSP-218x
RFS
TFS
The ADSP-218x family of DSPs can be interfaced directly to the
AD7680 without any glue logic required. The SPORT control
register should be set up as follows:
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 22. Interfacing to the ADSP-218x
TFSW = RFSW = 1, Alternate Framing
INVRFS = INVTFS = 1, Active Low Frame Signal
DTYPE = 00, Right Justify Data
SLEN = 0111, 8-Bit Data-Words
ISCLK = 1, Internal Serial Clock
TFSR = RFSR = 0, Frame First Word
IRFS = 0
The timer register is loaded with a value that provides an
interrupt at the required sample interval. When an interrupt is
received, the values in the transmit autobuffer start to be
transmitted and TFS is generated. The TFS is used to control
the RFS and therefore the reading of data. The data is stored in
the receive autobuffer for processing or to be shifted later. The
frequency of the serial clock is set in the SCLKDIV register.
When the instruction to transmit with TFS is given, i.e.,
TX0 = AX0, the state of the SCLK is checked. The DSP waits
until the SCLK has gone high, low, and high again before
transmission starts. If the timer and SCLK values are chosen
such that the instruction to transmit occurs on or near the
rising edge of SCLK, the data may be transmitted or it may wait
until the next clock edge.
ITFS = 1
To implement the power-down mode, SLEN should be set to
0111 to issue an 8-bit SCLK burst. The connection diagram is
shown in Figure 22. The ADSP-218x has the TFS and RFS of the
SPORT tied together, with TFS set as an output and RFS set as
Rev. A | Page 18 of 24
AD7680
APPLICATION HINTS
GROUNDING AND LAYOUT
as clocks, should be shielded with digital ground to avoid
radiating noise to other sections of the board, and clock signals
should never be run near the analog inputs. Avoid crossover of
digital and analog signals. Traces on opposite sides of the board
should run at right angles to each other, which reduces the
effects of feedthrough on the board. A microstrip technique is
by far the best but is not always possible with a double-sided
board. In this technique, the component side of the board is
dedicated to ground planes while the signals are placed on the
solder side.
The printed circuit board that houses the AD7680 should be
designed such that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes that can be separated easily. A minimum
etch technique is generally best for ground planes, because it
gives the best shielding. Digital and analog ground planes
should be joined at only one place. If the AD7680 is in a system
where multiple devices require an AGND to DGND
connection, the connection should still be made at one point
only, a star ground point that should be established as close as
possible to the AD7680.
Good decoupling is also very important. All analog supplies
should be decoupled with 10 μF tantalum in parallel with
0.1 μF capacitors to AGND, as discussed in the Typical
Connection Diagram section. To achieve the best performance
from these decoupling components, the user should attempt to
keep the distance between the decoupling capacitors and the
VDD and GND pins to a minimum, with short track lengths
connecting the respective pins.
Avoid running digital lines under the device because these
couple noise onto the die. The analog ground plane should be
allowed to run under the AD7680 to avoid noise coupling. The
power supply lines to the AD7680 should use as large a trace as
possible to provide low impedance paths and reduce the effects
of glitches on the power supply line. Fast switching signals, such
Rev. A | Page 19 of 24
AD7680
OUTLINE DIMENSIONS
3.00
2.90
2.80
6
1
5
2
4
3
3.00
2.80
2.60
1.70
1.60
1.50
PIN 1
INDICATOR
0.95 BSC
1.90
BSC
1.30
1.15
0.90
0.20 MAX
0.08 MIN
1.45 MAX
0.95 MIN
0.55
0.45
0.35
0.15 MAX
0.05 MIN
10°
4°
0°
SEATING
PLANE
0.60
BSC
0.50 MAX
0.30 MIN
COMPLIANT TO JEDEC STANDARDS MO-178-AB
Figure 23. 6-Lead Small Outline Transistor Package [SOT-23] (RJ-6) Dimensions shown in millimeters
3.20
3.00
2.80
8
1
5
4
5.15
4.90
4.65
3.20
3.00
2.80
PIN 1
IDENTIFIER
0.65 BSC
0.95
0.85
0.75
15° MAX
1.10 MAX
0.80
0.55
0.40
0.15
0.05
0.23
0.09
6°
0°
0.40
0.25
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 24. 8-Lead Micro Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
Rev. A | Page 20 of 24
AD7680
ORDERING GUIDE
Temperature
Range
Linearity
Package
Option
Model1
Error (LSB)2
Package Description
Branding
C40
CQA
CQA
CQA
C40
C3H
C3H
CQB
CQB
CQB
C3H
AD7680ARJZ-REEL7
AD7680ARM
AD7680ARM-REEL
AD7680ARM-REEL7
AD7680ARMZ
AD7680BRJZ-R2
AD7680BRJZ-REEL7
AD7680BRM
AD7680BRM-REEL
AD7680BRM-REEL7
AD7680BRMZ
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
14 Bits Min
14 Bits Min
14 Bits Min
14 Bits Min
14 Bits Min
15 Bits Min
15 Bits Min
15 Bits Min
15 Bits Min
15 Bits Min
15 Bits Min
15 Bits Min
15 Bits Min
6-Lead Small Outline Transistor Package (SOT-23)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
6-Lead Small Outline Transistor Package (SOT-23)
6-Lead Small Outline Transistor Package (SOT-23)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
8-Lead Mini Small Outline Package (MSOP)
RJ-6
RM-8
RM-8
RM-8
RM-8
RJ-6
RJ-6
RM-8
RM-8
RM-8
RM-8
RM-8
RM-8
AD7680BRMZ-REEL
AD7680BRMZ-REEL7
C3H
C3H
1 Z = RoHS Compliant Part.
2 Linearity error here refers to no missing codes.
Rev. A | Page 21 of 24
AD7680
NOTES
Rev. A | Page 22 of 24
AD7680
NOTES
Rev. A | Page 23 of 24
AD7680
NOTES
© 2004-2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D03643-0-5/11(A)
Rev. A | Page 24 of 24
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