MAX1455AUE [MAXIM]
Low-Cost Automotive Sensor Signal Conditioner; 低成本，汽车传感器信号调理器
| 型号： | MAX1455AUE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Low-Cost Automotive Sensor Signal Conditioner |
| 文件： | 总25页 (文件大小：288K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2088; Rev 1; 10/01
Low-Cost Automotive Sensor Signal
Conditioner
General Description
Features
The MAX1455 is a highly integrated automotive analog-
sensor signal processor for resistive element sensors.
The MAX1455 provides amplification, calibration, and
temperature compensation that enable an overall per-
formance approaching the inherent repeatability of the
sensor. The fully analog signal path introduces no
quantization noise in the output signal while enabling
digitally controlled trimming with integrated 16-bit digi-
tal-to-analog converters (DACs). Offset and span are
also calibrated using 16-bit DACs, allowing sensor
products to be truly interchangeable.
o Provides Amplification, Calibration, and
Temperature Compensation
o Selectable Output Clipping Limits
o Accommodates Sensor Output Sensitivities
from 5mV/V to 40mV/V
o Single-Pin Digital Programming
o No External Trim Components Required
o 16-Bit Offset and Span Calibration Resolution
o Fully Analog Signal Path
The MAX1455 architecture includes a programmable
sensor excitation, a 16-step programmable-gain ampli-
fier (PGA), a 768-byte (6144 bits) internal EEPROM,
four 16-bit DACs, an uncommitted op amp, and an on-
chip temperature sensor. In addition to offset and span
compensation, the MAX1455 provides a unique tem-
perature compensation strategy that was developed to
provide a remarkable degree of flexibility while minimiz-
ing testing costs.
o PRT Bridge Can Be Used for Temperature-
Correction Input
o On-Chip Lookup Table Supports Multipoint
Calibration Temperature Correction
o Fast 3.2kHz Frequency Response
o On-Chip Uncommitted Op Amp
The MAX1455 is available in die form, 16-pin SSOP and
TSSOP packages.
o Secure-Lock™ Prevents Data Corruption
Customization
Ordering Information
Maxim can customize the MAX1455 for high-volume
dedicated applications. Using our dedicated cell library
of more than 2000 sensor-specific function blocks,
Maxim can quickly provide a modified MAX1455 solu-
tion. Contact Maxim for further information.
PART
TEMP. RANGE
-40°C to +85°C
-40°C to +125°C
-40°C to +85°C
-40°C to +125°C
-40°C to +85°C
PIN-PACKAGE
16 TSSOP
16 TSSOP
16 SSOP
MAX1455EUE*
MAX1455AUE*
MAX1455EAE
MAX1455AAE
MAX1455C/D
16 SSOP
Dice**
Applications
Pressure Sensors and Transducers
Piezoresistive Silicon Sensors
Strain Gauges
*Future product—contact factory for availability.
**Dice are tested at T = +25°C, DC parameters only.
A
Resistive Element Sensors
Accelerometers
Humidity Sensors
Pin Configuration
TOP VIEW
MR and GMR Sensors
TEST1
OUT
INP
1
2
3
4
5
6
7
8
16 TEST2
15 TEST3
14 TEST4
13 DIO
Outputs
Ratiometric Voltage Output
Programmable Output Clip Limits
BDR
INM
MAX1455
12 UNLOCK
V
11
10 AMP-
AMPOUT
V
SS
DD2
V
DD1
A detailed Functional Diagram appears at end of data sheet.
AMP+
9
Secure-Lock is a trademark of Maxim Integrated Products, Inc.
SSOP/TSSOP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Low-Cost Automotive Sensor Signal
Conditioner
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
to V .......................................-0.3V, +6V
Operating Temperature Ranges (T
to T
)
MAX
DD_
SS
MIN
V
- V
..............................................................-0.3V, +0.6V
MAX1455EUE ..................................................-40°C to +85°C
MAX1455AUE................................................-40°C to +125°C
MAX1455C/D...................................................-40°C to +85°C
MAX1455EAE ..................................................-40°C to +85°C
MAX1455AAE ................................................-40°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°C
DD1
DD2
All Other Pins..................................(V - 0.3V) to (V
Short-Circuit Duration, OUT, BDR, AMPOUT.............Continuous
Continuous Power Dissipation (T = +70°C)
+ 0.3V)
DD_
SS
A
16-Pin SSOP (derate 8.00mW/°C above +70°C) .........640mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
CONDITIONS
MIN
4.5
TYP
MAX
UNITS
GENERAL CHARACTERISTICS
Supply Voltage
V
5.0
3.0
1
5.5
6.0
V
DD
Supply Current
I
I
+ I
DD2
(Note 1)
mA
MHz
DD
DD1
Oscillator Frequency
f
0.85
1.15
OSC
ANALOG INPUT
Input Impedance
R
1
MΩ
IN
Input-Referred Adjustable Offset
Range
Offset TC = 0 (Note 2), minimum gain
= T to T
150
mV
Input-Referred Offset Tempco
Amplifier Gain Nonlinearity
T
A
1
µV/°C
MIN
MAX
0.025
%
Specified for common-mode voltages
Common-Mode Rejection Ratio
CMRR
90
7
dB
between V and V
SS
DD
Minimum Input-Referred FSO
Range
(Note 3)
(Note 3)
mV/V
mV/V
Maximum Input-Referred FSO
Range
40
ANALOG OUTPUT
Minimum Differential Signal-
Gain Range
PGA [3:0] = 0000
PGA [3:0] = 1111
39
V/V
V/V
Maximum Differential Signal-
Gain Range
234
Low
High
Low
High
Low
High
Low
High
0.10
4.90
0.15
4.85
0.20
4.80
0.25
4.75
Clip[1:0] = 00
Clip[1:0] = 01
Clip[1:0] = 10
Clip[1:0] = 11
No load,
Output Clip Voltage Settings
V
V
OUT
T
= T
to T
A
MIN MAX
V
=+0.5V to +4.5V, T = T
to T
,
MAX
OUT
A
MIN
Load Current Source
1
mA
Clip[1:0] = 00
2
_______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
CONDITIONS
=+0.5V to +4.5V, T = T
Clip[1:0] = 00
MIN
TYP
MAX
UNITS
V
to T
,
MAX
OUT
A
MIN
Load Current Sink
2
mA
DC Output Impedance
Offset DAC Output Ratio
Offset TC DAC Output Ratio
Step Response
1
Ω
∆V
∆V
/∆ODAC
1.0
1.0
300
V/V
V/V
µs
OUT
OUT
/∆OTCDAC
0% to 63% of final value
Output Capacitive Load
1000
nF
DC to 1kHz (gain = minimum, source
impedance = 5kΩ)
Output Noise
2.5
mV
RMS
BRIDGE DRIVE
Bridge Current
I
V
≤ 3.75V
BDR
0.1
0.5
12
2
mA
mA/mA
Hex
BDR
Current Mirror Ratio
Minimum FSODAC Code
Recommended minimum value
4000
DIGITAL-TO-ANALOG CONVERTERS
DAC Resolution
16
Bits
∆V
/ ∆CODE, DAC reference = V
=
=
=
=
OUT
DD
ODAC Bit Weight
153
µV/Bit
+5.0V (Note 4)
∆V / ∆CODE, DAC reference = V
OUT
BDR
OTCDAC Bit Weight
FSODAC Bit Weight
FSOTCDAC Bit Weight
76
153
76
µV/Bit
µV/Bit
µV/Bit
2.5V (Note 4)
∆V / ∆CODE, DAC reference = V
+5.0V (Note 4)
OUT
DD
∆V / ∆CODE, DAC reference = V
OUT
BDR
2.5V (Note 4)
COARSE-OFFSET DAC
IRODAC Resolution
Excluding sign bit
3
9
Bits
∆V
/∆CODE, input referred,
OUT
IRODAC Bit Weight
mV/Bit
DAC reference = V
= +5.0V (Note 4)
DD
INTERNAL RESISTORS
Current-Source Reference
R
75
75
kΩ
kΩ
ISRC
Full-Span Output (FSO) Trim
Resistor
∆R
STC
Resistor Temperature Coefficient
Minimum Resistance Value
Maximum Resistance Value
Resistor Matching
Applies to R
Applies to R
Applies to R
and ∆R
and ∆R
and ∆R
1333
60
ppm/°C
kΩ
ISRC
ISRC
ISRC
STC
STC
STC
STC
90
kΩ
R
ISRC
to ∆R
1
%
AUXILIARY OP AMP
Open-Loop Gain
90
dB
V
Input Common-Mode Range
V
V
V
DD
CM
SS
V
0.01
+
V
0.01
-
DD
SS
Output Swing
No load, T = T
to T
V
A
MIN
MAX
_______________________________________________________________________________________
3
Low-Cost Automotive Sensor Signal
Conditioner
ELECTRICAL CHARACTERISTICS (continued)
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD
PARAMETER
SYMBOL
CONDITIONS
= (V + 0.25) to (V - 0.25)
MIN
TYP
MAX
UNITS
mA
Output Current Drive
V
V
V
-1
+1
OUT
CM
SS
DD
Common-Mode Rejection Ratio
CMRR
= V to V
70
1
dB
SS
DD
T
T
= +25°C
20
25
A
A
= 2.5V unity-gain
buffer (Note 5)
IN
Input Offset Voltage
V
mV
OS
= T
to T
MAX
MIN
Unity-Gain Bandwidth
2
MHz
TEMPERATURE-TO-DIGITAL CONVERTER
Temperature ADC Resolution
Offset
8
3
Bits
Bits
Gain
1.45
1
°C/Bit
LSB
Hex
Nonlinearity
Lowest Digital Output
Highest Digital Output
EEPROM
00
AF
Hex
Maximum Erase/Write Cycles
Erase Time
(Notes 6, 7)
(Note 8)
10k
Cycles
ms
7.1
Note 1: Excludes sensor or load current.
Note 2: This is the maximum allowable sensor offset.
Note 3: This is the sensor’s sensitivity normalized to its drive voltage, assuming a desired full-span output of 4V and a bridge voltage of 2.5V.
Note 4: Bit weight is ratiometric to V
.
DD
Note 5: All units production tested at T = +25°C. Limits over temperature are guaranteed by design.
A
Note 6: Programming of the EEPROM at temperatures below +70°C is recommended.
Note 7: For operation above +70°C, limit erase/write cycle to 100.
Note 8: All erase commands require 7.1ms minimum time.
Typical Operating Characteristics
(V
= +5V, V = 0, T = +25°C, unless otherwise noted.)
SS A
DD_
OFFSET DAC DNL
OUTPUT NOISE
AMPLIFIER GAIN NONLINEARITY
2.5
2.0
1.5
1.0
0.5
0
5.0
2.5
0
INP - INM SHORTED TOGETHER
PGA = 0HEX
ODAC = +6000HEX
OTCDAC = 0
FSODAC = 6000HEX
FSOTCDAC = 8000HEX
IRO = 2HEX
PGA = 0
OUT
10mV/div
-0.5
-1.0
-1.5
-2.0
-2.5
-2.5
-5.0
0
10k 20k 30k 40k 50k 60k 70k
DAC CODE
400µs/div
-50
-30
-10
10
30
50
INPUT VOLTAGE [INP - INM] (mV)
4
_______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Pin Description
PIN
NAME
FUNCTION
TEST1,
TEST3,
TEST2
1, 15, 16
Test Pins. Connect to V or leave unconnected.
SS
Analog Output. Internal voltage nodes can be accessed in digital mode. OUT can be parallel
connected to DIO. Bypass OUT to ground with a 0.1µF capacitor to reduce output noise.
2
OUT
3
4
INP
BDR
INM
Positive Input. Can be swapped to INM by the Configuration register.
Bridge Drive Output
5
Negative Input. Can be swapped to INP by the Configuration register.
Negative Supply Voltage
6
V
SS
7
V
Positive Supply Voltage 1. Connect a 0.1µF capacitor from V
Auxiliary Op Amp Positive Input
to V
.
SS
DD1
DD
8
AMP+
AMPOUT
AMP-
9
Auxiliary Op Amp Output
10
Auxiliary Op Amp Negative Input
Positive Supply Voltage 2. Connect a 0.47µF capacitor from V
to V . Connect V
to V
or
DD1
DD2
.
SS
DD2
11
12
V
DD2
for improved noise performance, connect a 1kΩ resistor to V
DD1
Secure-Lock Disable. There is a 150µA pulldown to V . Connect to V
SS
and enable serial communication.
to disable Secure-Lock
DD
UNLOCK
Digital Input Output. Single-pin serial communication port. There are no internal pullups on DIO.
13
14
DIO
Connect pullup resistor from DIO to V
when in digital mode.
DD
TEST4
Test Pin. Do not connect.
EEPROM locations corrects performance in 1.5°C tem-
perature increments over a range of -40°C to +125°C.
For sensors that exhibit a characteristic temperature
performance, a select number of calibration points can
be used with a number of preset values that define the
temperature curve. The sensor and the MAX1455
should be at the same temperature during calibration
and use. This allows the electronics and sensor errors
to be compensated together and optimizes perfor-
mance. For applications where the sensor and elec-
tronics are at different temperatures, the MAX1455 can
use the sensor bridge as an input to correct for temper-
ature errors.
Detailed Description
The MAX1455 provides amplification, calibration, and
temperature compensation to enable an overall perfor-
mance approaching the inherent repeatability of the
sensor. The fully analog signal path introduces no
quantization noise in the output signal while enabling
digitally controlled trimming with the integrated 16-bit
DACs. The MAX1455 includes four selectable high/low
clipping limits set in discrete 50mV steps from
0.1V/4.9V to 0.25V/4.75V. Offset and span can be cali-
brated to within 0.02% of span.
The MAX1455 architecture includes a programmable
sensor excitation, a 16-step PGA, a 768-byte (6144 bits)
internal EEPROM, four 16-bit DACs, an uncommitted op
amp, and an on-chip temperature sensor. The MAX1455
also provides a unique temperature compensation strat-
egy that was developed to provide a remarkable degree
of flexibility while minimizing testing costs.
The single pin, serial DIO communication architecture
and the ability to timeshare its activity with the sensor’s
output signal enables output sensing and calibration
programming on a single line by parallel connecting
OUT and DIO. The MAX1455 provides a Secure-Lock
feature that allows the customer to prevent modification
of sensor coefficients and the 52-byte user-definable
EEPROM data after the sensor has been calibrated.
The Secure-Lock feature also provides a hardware
override to enable factory rework and recalibration by
assertion of logic high on the UNLOCK pin.
The customer can select from 1 to 114 temperature
points to compensate their sensor. This allows the lati-
tude to compensate a sensor with a simple first-order
linear correction or match an unusual temperature
curve. Programming up to 114 independent 16-bit
_______________________________________________________________________________________
5
Low-Cost Automotive Sensor Signal
Conditioner
The MAX1455 allows complete calibration and sensor
verification to be performed at a single test station. Once
calibration coefficients have been stored in the ASIC, the
BIAS
TEST 1
TEST 2
TEST 3
TEST 4
GENERATOR
IRO
customer can choose to retest in order to verify perfor-
MAX1455
OSCILLATOR
DAC
mance as part of a regular QA audit or to generate final
test data on individual sensors. In addition, Maxim has
developed a pilot production test system to reduce time
to market. Engineering test evaluation and pilot produc-
tion of the MAX1455 can be performed without expending
the cost and time to develop in-house test capabilities.
Contact Maxim for additional information.
CLIP-TOP
INP
PGA
OUT
∑
INM
CLIP-BOT
CURRENT
SOURCE
ANAMUX
Frequency response can be user adjusted to values
lower than the 3.2kHz bandwidth by using the uncom-
mitted op amp and simple passive components.
BDR
TEMP
176-POINT
SENSOR
TEMPERATURE-
INDEXED
The MAX1455 (Figure 1) provides an analog amplifica-
tion path for the sensor signal. It uses a digitally con-
trolled analog path for nonlinear temperature correction.
For PRT applications, analog architecture is available for
first-order temperature correction. Calibration and cor-
rection are achieved by varying the offset and gain of a
PGA and by varying the sensor bridge excitation current
or voltage. The PGA utilizes a switched capacitor CMOS
technology, with an input-referred offset trimming range
of more than 150mV with an approximate 3µV resolution
(16 bits). The PGA provides gain values from 39V/V to
234V/V in 16 steps.
FSO
COEFFICIENTS
8-BIT A/D
176-POINT
TEMPERATURE-
INDEXED
OFFSET
V
DD1
COEFFICIENTS
V
DD2
416 BITS FOR
AMP-
USER DATA
CONTROL
DIO
UNLOCK
CONFIG REG
AMPOUT
6144-BIT
EEPROM
V
SS
AMP+
The MAX1455 uses four 16-bit DACs with calibration
coefficients stored by the user in an internal 768 x 8
EEPROM (6144 bits). This memory contains the follow-
ing information, as 16-bit-wide words:
Figure 1. Functional Diagram
transferred to the offset DAC register. The resulting volt-
age is fed into a summing junction at the PGA output,
compensating the sensor offset with a resolution of
76µV ( 0.0019% FSO). If the offset TC DAC is set to
zero, then the maximum temperature error is equivalent
to 1°C of temperature drift of the sensor, given that the
Offset DAC has corrected the sensor every 1.5°C. The
temperature indexing boundaries are outside the speci-
fied absolute maximum ratings. The minimum indexing
value is 00hex, corresponding to approximately -69°C.
All temperatures below this value output the coefficient
value at index 00hex. The maximum indexing value is
AFhex, which is the highest lookup table entry. All tem-
peratures higher than approximately +184°C output the
highest lookup table index value. No indexing wrap-
around errors are produced.
•
•
•
•
•
•
Configuration register
Offset calibration coefficient table
Offset temperature coefficient register
FSO calibration coefficient table
FSO temperature correction register
52 bytes (416 bits) uncommitted for customer pro-
gramming of manufacturing data (e.g., serial num-
ber and date)
Offset Correction
Initial offset correction is accomplished at the input
stage of the signal gain amplifiers by a coarse offset
setting. Final offset correction occurs through the use of
a temperature-indexed lookup table with one hundred
seventy-six 16-bit entries. The on-chip temperature sen-
sor provides a unique 16-bit offset trim value from the
table with an indexing resolution of approximately 1.5°C
from -40°C to +125°C. Every millisecond, the on-chip
temperature sensor provides indexing into the offset
lookup table in EEPROM and the resulting value is
FSO Correction
Two functional blocks control the FSO gain calibration.
First, a coarse gain is set by digitally selecting the gain of
the PGA. Second, FSODAC sets the sensor bridge cur-
rent or voltage with the digital input obtained from a tem-
perature indexed reference to the FSO lookup table in
EEPROM. FSO correction occurs through the use of a
6
_______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
temperature indexed lookup table with one hundred
changing the FSO affects the offset due to the nature of
the bridge. The temperature is measured on both the
MAX1455 die and at the bridge sensor. It is recom-
mended to compensate the first-order temperature
errors using the bridge sensor temperature.
seventy-six 16-bit entries. The on-chip temperature sen-
sor provides a unique FSO trim from the table with an
indexing resolution approaching one 16-bit value every
1.5°C from -40°C to +125°C. The temperature indexing
boundaries are outside the specified absolute maximum
ratings. The minimum indexing value is 00hex, corre-
sponding to approximately -69°C. All temperatures below
this value output the coefficient value at index 00hex. The
maximum indexing value is AFhex, which is the highest
lookup table entry. All temperatures higher than approxi-
mately +184°C output the highest lookup table index
value. No indexing wraparound errors are produced.
Typical Ratiometric
Operating Circuit
Ratiometric output configuration provides an output that is
proportional to the power-supply voltage. This output can
then be applied to a ratiometric ADC to produce a digital
value independent of supply voltage. Ratiometricity is an
important consideration for battery-operated instruments,
automotive, and some industrial applications.
Linear and Nonlinear Temperature
Compensation
The MAX1455 provides a high-performance ratiometric
output with a minimum number of external components
(Figure 2). These external components include the fol-
lowing:
Writing 16-bit calibration coefficients into the offset TC
and FSOTC registers compensates first-order tempera-
ture errors. The piezoresistive sensor is powered by a
current source resulting in a temperature-dependent
bridge voltage due to the sensor’s temperature coeffi-
cient resistance (TCR). The reference inputs of the off-
set TC DAC and FSOTC DAC are connected to the
bridge voltage. The DAC output voltages track the
bridge voltage as it varies with temperature, and by
varying the offset TC and FSOTC digital code and a
portion of the bridge voltage, which is temperature
dependent, is used to compensate the first-order tem-
perature errors.
•
•
One supply bypass capacitor
One optional output EMI suppression capacitor
Typical Nonratiometric
Operating Circuit
(5.5VDC < VPWR < 28VDC)
Nonratiometric output configuration enables the sensor
power to vary over a wide range. A low-dropout voltage
regulator, such as the MAX1615, is incorporated in the
circuit to provide a stable supply and reference for
MAX1455 operation. A typical example is shown in
Figure 3. Nonratiometric operation is valuable when
wide ranges of input voltage are to be expected and
the system A/D or readout device does not enable
ratiometric operation.
The internal feedback resistors (R
and R
) for
STC
ISRC
FSO temperature compensation are set to 75kΩ.
To calculate the required offset TC and FSOTC com-
pensation coefficients, two test temperatures are need-
ed. After taking at least two measurements at each
temperature, calibration software (in a host computer)
calculates the correction coefficients and writes them to
the internal EEPROM.
Internal Calibration Registers
The MAX1455 has five 16-bit internal calibration regis-
ters (ICRs) that are loaded from EEPROM, or loaded
from the serial digital interface.
With coefficients ranging from 0000hex to FFFFhex and
a +5V reference, each DAC has a resolution of 76µV.
Two of the DACs (offset TC and FSOTC) utilize the sen-
sor bridge voltage as a reference. Since the sensor
bridge voltage is approximately set to +2.5V, the FSOTC
and offset TC exhibit a step size of less than 38µV.
Data can be loaded into the ICRs under three different
circumstances.
Normal Operation, Power-On Initialization Sequence:
•
The MAX1455 has been calibrated, the Secure-
Lock byte is set (CL[7:0] = FFhex), and UNLOCK is
low.
For high-accuracy applications (errors less than
0.25%), the first-order offset TC and FSOTC should be
compensated with the offset TC and FSOTC DACs, and
the residual higher order terms with the lookup table.
The offset and FSO compensation DACs provide
unique compensation values for approximately 1.5°C of
temperature change as the temperature indexes the
address pointer through the coefficient lookup table.
Changing the offset does not affect the FSO; however,
•
•
Power is applied to the device.
The power-on reset (POR) functions have been
completed.
•
Registers CONFIG, OTCDAC, and FSOTCDAC are
refreshed from EEPROM.
_______________________________________________________________________________________
7
Low-Cost Automotive Sensor Signal
Conditioner
+5V V
DD
7
V
DD1
4
3
11
2
BDR
INP
V
DD2
OUT
OUT
MAX1455
5
SENSOR
INM
0.1µF
0.1µF
V
SS
6
GND
Figure 2. Basic Ratiometric Output Configuration
1
VPWR
IN
MAX1615
+5.5V TO +28V
5
SHDN
3
OUT
4
5/3
GND
2
7
1kΩ
V
DD1
4
5
11
2
V
BDR
INM
DD2
OUT
OUT
MAX1455
3
SENSOR
INP
0.1µF
0.1µF
0.1µF
0.47µF
V
SS
6
GND
Figure 3. Basic Nonratiometric Output Configuration
•
Registers ODAC and FSODAC are refreshed from
the temperature indexed EEPROM locations.
•
Registers ODAC and FSODAC are refreshed from
the temperature indexed EEPROM locations.
Normal Operation, Continuous Refresh:
Calibration Operation, Registers Updated by Serial
Communications:
•
The MAX1455 has been calibrated, the Secure-
Lock byte has been set (CL[7:0] = FFhex), and
UNLOCK is low.
•
The MAX1455 has not had the Secure-Lock byte set
(CL[7:0] = 00hex) or UNLOCK is high.
•
•
•
Power is applied to the device.
•
•
•
Power is applied to the device.
The POR functions have been completed.
The POR functions have been completed.
The temperature index timer reaches a 1ms time
period.
The registers can then be loaded from the serial
digital interface by use of serial commands. See the
section on serial I/O and commands.
•
Registers CONFIG, OTCDAC, and FSOTCDAC are
refreshed from EEPROM.
8
_______________________________________________________________________________________
Low-Cost Precision Sensor Signal
Conditioner
Secure-Lock byte (CL[7:0] = 00hex) configures the DIO
as an asynchronous serial input for calibration and test
purposes.
Internal EEPROM
The internal EEPROM is organized as a 768 by 8-bit
memory. It is divided into 12 pages, with 64 bytes per
page. Each page can be individually erased. The memo-
ry structure is arranged as shown in Table 1. The look-up
tables for ODAC and FSODAC are also shown, with the
respective temperature index pointer. Note that the
ODAC table occupies a continuous segment, from
address 000hex to address 15Fhex, whereas the
FSODAC table is divided in two parts, from 200hex to
2FFhex, and from 1A0hex to 1FFhex. With the exception
of the general-purpose user bytes, all values are 16-bit-
wide words formed by two adjacent byte locations (high
byte and low byte).
MAX1455 Digital Mode
A single-pin serial interface provided by the DIO
accesses the MAX1455’s control functions and memo-
ry. All command inputs to this pin flow into a set of 16
registers, which form the interface register set (IRS).
Additional levels of command processing are provided
by control logic, which takes its inputs from the IRS. A
bidirectional 16-bit latch buffers data to and from the
16-bit Calibration registers and internal (8-bit-wide)
EEPROM locations. Figure 5 shows the relationship
between the various serial commands and the
MAX1455 internal architecture.
The MAX1455 compensates for sensor offset, FSO, and
temperature errors by loading the internal calibration
registers with the compensation values. These com-
pensation values can be loaded to registers directly
through the serial digital interface during calibration or
loaded automatically from EEPROM at power-on. In this
way, the device can be tested and configured during cal-
ibration and test and the appropriate compensation val-
ues stored in internal EEPROM. The device autoloads the
registers from EEPROM and is ready for use without fur-
ther configuration after each power-up. The EEPROM is
configured as an 8-bit-wide array so each of the 16-bit
registers is stored as two 8-bit quantities. The
Configuration register, FSOTCDAC, and OTCDAC regis-
ters are loaded from the preassigned locations in the
EEPROM. Table 2 is the EEPROM ODAC and FSODAC
lookup table memory map.
Communication Protocol
The DIO serial interface is used for asynchronous serial
data communications between the MAX1455 and a host
calibration test system or computer. The MAX1455 auto-
matically detects the baud rate of the host computer
when the host transmits the initialization sequence. Baud
rates between 4800 and 38400 can be detected and
used. The data format is always 1 start bit, 8 data bits,
and 1 stop bit. The 8 data bits are transmitted LSB first,
MSB last. A weak pullup resistor can be used to maintain
logic 1 on the DIO pin while the MAX1455 is in digital
mode. This is to prevent unintended 1 to 0 transitions on
this pin, which would be interpreted as a communication
start bit. Communications are only allowed when the
Secure-Lock byte is disabled (i.e., CL[7:0] = 00HEX ) or
UNLOCK is held high. Table 8 is the control location.
The ODAC and FSODAC are loaded from the EEPROM
lookup tables using an index pointer that is a function
of temperature. An ADC converts the integrated tem-
perature sensor to an 8-bit value every 1ms. This digi-
tized value is then transferred into the Temp-Index
register. Table 3 lists the registers.
Initialization Sequence
The first Command Byte sent to the MAX1455 after
power-up, or following receipt of the reinitialization
command, is used by the MAX1455 to learn the com-
munication baud rate. The initialization sequence is a 1-
byte transmission of 01 hex, as follows:
The typical transfer function for the temp-index is as fol-
lows:
temp-index = 0.69 ✕ Temperature (°C) + 47.58
1 1 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 1
0 1
where temp-index is truncated to an 8-bit integer value.
Typical values for the Temp-Index register are given in
Table 4.
The start bit, shown in bold above, initiates the baud rate
synchronization. The 8 data bits 01hex (LSB first) follow
this and then the stop bit, also shown in bold above. The
MAX1455 uses this sequence to calculate the time inter-
val for a 1-bit transmission as a multiple of the period of
its internal oscillator. The resulting number of oscillator
clock cycles is then stored internally as an 8-bit number
(BITCLK). Note that the device power supply should be
stable for a minimum period of 1ms before the initializa-
tion sequence is sent. This allows time for the POR func-
tion to complete and DIO to be configured by the
Secure-Lock byte or UNLOCK.
Note that the EEPROM is 1 byte wide and the registers
that are loaded from EEPROM are 16 bits wide. Thus,
each index value points to 2 bytes in the EEPROM.
Maxim programs all EEPROM locations to FFhex with
the exception of the oscillator frequency setting and
Secure-Lock byte. OSC[2:0] is in the Configuration
register (Table 5). These bits should be maintained at
the factory-preset values. Programming 00hex in the
_______________________________________________________________________________________
9
Low-Cost Automotive Sensor Signal
Conditioner
Table 1. EEPROM Memory Address Map
LOW-BYTE
ADDRESS (hex)
HIGH-BYTE
ADDRESS (hex)
TEMP-INDEX[7:0]
(hex)
PAGE
CONTENTS
000
03E
040
07E
080
0BE
0C0
0FE
100
13E
140
15E
160
162
164
166
168
16A
16C
17E
180
19E
1A0
1BE
1C0
1FE
200
23E
240
27E
280
2BE
2C0
2FE
001
03F
041
07F
081
0BF
0C1
0FF
101
13F
141
15F
161
163
165
167
169
16B
16D
17F
181
19F
1A1
1BF
1C1
1FF
201
23F
241
27F
281
2BF
2C1
2FF
00
1F
0
1
2
3
4
20
3F
40
5F
ODAC
Lookup Table
60
7F
80
9F
A0
AF to FF
Configuration
Reserved
OTCDAC
5
Reserved
FSOTCDAC
Control Location
52 General-Purpose
User Bytes
6
80
8F
90
7
8
9
A
B
AF to FF
00
FSODAC
Lookup Table
1F
20
3F
40
5F
60
7F
10 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Table 2. EEPROM ODAC and FSODAC Lookup Table Memory Map
EEPROM ADDRESS ODAC
LOW BYTE AND HIGH BYTE
EEPROM ADDRESS FSODAC
LOW BYTE AND HIGH BYTE
TEMP-INDEX[7:0]
00hex
to
000hex and 001hex
to
200hex and 201hex
to
7Fhex
0FEhex and 0FFhex
2FEhex and 2FFhex
80hex
to
100hex and 101hex
to
1A0hex and 1A1hex
to
AFhex
15Ehex and 15Fhex
1FEhex and 1FFhex
Table 3. Registers
REGISTER
CONFIG
DESCRIPTION
Configuration register
ODAC
Offset DAC register
OTCDAC
Offset temperature coefficient DAC register
Full-span output DAC register
FSODAC
FSOTCDAC
Full-span output temperature coefficient DAC register
Reinitialization Sequence
The MAX1455 provides for reestablishing, or relearning,
the baud rate. The reinitialization sequence is a 1-byte
transmission of FFhex, as follows:
Table 4. Temp-Index Typical Values
TEMP-INDEX[7:0]
TEMPERATURE
(°C)
DECIMAL
20
HEXADECIMAL
-40
+25
+85
+125
14
41
6A
86
1
1
1
1
1
1
1
1
1
1
1
1
1
1 1 1 1 1
1
0
65
When a serial reinitialization sequence is received, the
receive logic resets itself to its power-up state and
waits for the initialization sequence. The initialization
sequence must follow the reinitialization sequence in
order to reestablish the baud rate.
106
134
WEAK PULLUP
REQUIRED
WEAK PULLUP
REQUIRED
DATA
0
0 0 0 0 0 0 0 0
0
1 1 1 1 1 0 1 0 0 1 1 0 1 11 1 1 1 1 1 1 1 1
1
1 1 1 1 1 1 1 1 1 XX
XX
HIGH-Z
DIO
RECEIVE
RECEIVE
TRANSMIT
HIGH-Z
HIGH-Z
HOST
TRANSMIT
TRANSMIT
RECEIVE
Figure 4. DIO Output Data Format
______________________________________________________________________________________ 11
Low-Cost Automotive Sensor Signal
Conditioner
Table 5. Configuration Register (CONFIG[15:0])
FIELD
15:13
12:11
10
NAME
OSC[2:0]
CLIP[1:0]
PGA Sign
IRO Sign
IRO[2:0]
DESCRIPTION
Oscillator frequency setting. Factory preset; do not change.
Sets output clip levels.
Logic 1 inverts INM and INP polarity (Table 6).
9
Logic 1 for positive input-referred offset (IRO). Logic 0 for negative IRO.
Input-referred coarse-offset adjustment (Table 7).
Programmable-gain amplifier setting.
8:6
5:2
PGA[3:0]
ODAC Sign
1
Logic 1 for positive offset DAC output. Logic 0 for negative offset DAC output.
OTCDAC
Sign
0
Logic 1 for positive offset TC DAC output. Logic 0 for negative offset TC DAC output.
contents of the IRS and comprises a 4-bit interface reg-
ister set address (IRSA) nibble and a 4-bit interface
register set data (IRSD) nibble. The IRS Command Byte
is structured as follows:
Table 6. PGA Gain Setting (PGA[3:0])
PGA[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
PGA GAIN (V/V)
39
52
IRS[7:0] = IRSD[3:0], IRSA[3:0]
All commands are transmitted LSB first. The first bit fol-
lowing the start bit is IRSA[0] and the last bit before the
stop bit is IRSD[3] as follows:
65
78
IRSA
IRSD
91
1
1
1
1
1
0
1
2
3
0
1
2
3
1 1 1 1 1
1
0
104
117
130
143
156
169
182
195
208
221
234
Half of the register contents of the IRS are used for data
hold and steering information. Data writes to two loca-
tions within the IRS cause immediate action (command
execution). These locations are at addresses 9 and 15
and are the Command Register to Internal Logic (CRIL)
and reinitialize commands, respectively. Table 9 shows
a full listing of IRS address decoding.
Command sequences can be written to the MAX1455
as a continuous stream, i.e., start bit, command byte,
stop bit, start bit, command byte, stop bit, etc. There
are no delay requirements between commands while
the MAX1455 is receiving data.
Command Register to Internal Logic
A data write to the CRIL location (IRS address 9) causes
immediate execution of the command associated with
the 4-bit data nibble written. All EEPROM and Calibration
register read and write, together with EEPROM erase,
commands are handled through the CRIL location. CRIL
is also used to enable the MAX1455 analog output and
to place output data (serial digital output) on DIO. Table
10 shows a full listing of CRIL commands.
Serial Interface Command Format
All communication commands into the MAX1455 follow
the format of a start bit, 8 command bits (command
byte), and a stop bit. The Command Byte controls the
12 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Table 7. Input Referred Offset (IRO[2:0])
INPUT-REFERRED OFFSET
INPUT-REFERRED OFFSET, CORRECTION
IRO SIGN, IRO[2:0]
CORRECTION AS % OF V
AT V = 5VDC IN mV
DD
DD
1,111
1,110
1,101
1,100
1,011
1,010
1,001
1,000
0,000
0,001
0,010
0,011
0,100
0,101
0,110
0,111
+1.25
+1.08
+0.90
+0.72
+0.54
+0.36
+0.18
0
+63
+54
+45
+36
+27
+18
+9
0
0
0
-0.18
-0.36
-0.54
-0.72
-0.90
-1.08
-1.25
-9
-18
-27
-36
-45
-54
-63
Note that there are time intervals before and after the
MAX1455 sends the data byte when all devices on the
DIO line are three-stated. It is recommended that a
weak pullup resistor be applied to the DIO line during
these time intervals to prevent unwanted transitions
(Figure 4). In applications where DIO and analog out-
put (OUT) are not connected, a pullup resistor should
be permanently connected to DIO. If the MAX1455 DIO
and analog outputs are connected, then do not load
this common line during analog measurements. In this
situation, perform the following sequence:
Serial Digital Output
DIO is configured as a digital output by writing a Read
IRS (RDIRS) command (5 hex) to the CRIL location. On
receipt of this command, the MAX1455 outputs a byte
of data, the contents of which are determined by the
IRS pointer (IRSP[3:0]) value at location IRSA[3:0] =
8hex. The data is output as a single byte, framed by a
start bit and a stop bit. Table 11 lists the data returned
for each IRSP address value.
Once the RDIRS command has been sent, all connec-
tions to DIO must be three-stated to allow the MAX1455
to drive the DIO line. Following receipt of the RDIRS
command, the MAX1455 drives DIO high after 1 byte
time. The MAX1455 holds DIO high for a single bit time
and then asserts a start bit (drives DIO low). The start
bit is then followed by the data byte and a stop bit.
Immediately following transmission of the stop bit, the
MAX1455 three-states DIO, releasing the line. The
MAX1455 is then ready to receive the next command
sequence 1 byte time after release of DIO.
1) Connect a pullup resistor to the DIO/OUT line,
preferably with a relay.
2) Send the RDIRS command.
3) Three-state the user connection (set to high imped-
ance).
4) Receive data from the MAX1455.
5) Activate the user connection (pull DIO/OUT line high).
6) Release the pullup resistor.
______________________________________________________________________________________ 13
Low-Cost Automotive Sensor Signal
Conditioner
DIO
IRS COMMAND (8 BITS)
IRSA [3:0] IRSD [3:0]
DHR [7:0]
0000
0001
0010
0011
0100
0101
DHR [3:0]
DHR [7:4]
DHR [11:8]
DHR [15:12]
RESERVED
RESERVED
ICRA [3:0]
IEEA [3:0]
IEEA [7:4]
BIDIRECTIONAL
16-BIT
DHR [15:8]
DATA
LATCH
ICRA [3:0] CALIBRATION REGISTER
0000
0001
0010
0011
0100
0101 TO
1111
EEPROM
MEMORY
768 X 8 BITS
0110
0111
1000
CONFIG
ODAC
OTCDAC
FSODAC
FSOTCDAC
IRSP [3:0]
IEEA [9:8]
CRIL [3.0]
(EXECUTE)
1001
ADDR DATA
RESERVED
1010
1011
ATIM [3:0]
ALOC [3:0]
TABLE 16. INTERNAL CALIBRATION
REGISTERS
1100 TO
1110
RESERVED
RELEARN
BAUD RATE
CRIL [3:0]
0000
FUNCTION
LOAD ICR
1111
TABLE 9. INTERFACE REGISTER
SET COMMANDS
0001
0010
0011
0100
0101
0110
0111
WRITE EEPROM
ERASE EEPROM
READ ICR
READ EEPROM
READ IRS
ANALOG OUT
ERASE PAGE
LOOKUP
ADDRESS
TEMP INDEX [7:0]
ENABLE ANALOG OUTPUT
1000 TO
1111
RESERVED
TABLE 10. CRIL ACTIONS
OUTPUT
TIMER
OUT
OUTPUT
MUX
IRSP [3:0]
0000
RETURNS
DHR [7:0]
PGA
0001
DHR [F:8]
0010
0011
0100
0101
IEEA [7:4], ICRA [3:0]
CRIL [3:0], IRSP [3:0]
ALOC [3:0], ATIM [3.0]
IEEA [7:0]
0110
IEED [7:0]
0111
1000
TEMP-INDEX [7:0]
BITCLK [7:0]
1001
1010 TO
1111
RESERVED
11001010 - (USE TO
CHECK COMMUNICATION)
TABLE 11. IRS POINTER FUNCTIONS (READS)
Figure 5. MAX1455 Serial Command Structure and Hardware Schematic
Figure 4 shows an example transmit/receive sequence
with the RDIRS command (59hex) being sent and the
MAX1455 responding with a byte value of 10hex.
mode, the internal registers are automatically refreshed
from the EEPROM.
When starting the MAX1455 in digital mode, pay spe-
cial attention to the 3 CLK bits: 3MSBs of the
Configuration register. The frequency of the MAX1455
internal oscillator is measured during production testing
and a 3-bit adjustment (calibration) code is calculated
Internal Clock Settings
Following initial power-up, or after a power reset, all of
the calibration registers within the MAX1455 contain
0000hex and must be programmed. Note that in analog
14 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Table 8. Control Location (CL[15:0])
FIELD
NAME
DESCRIPTION
15:8
CL[15:8]
Reserved
Control Location. Secure-Lock is activated by setting this to FFhex, which disables DIO serial
communications and connects OUT to PGA output.
7:0
CL[7:0]
Table 9. IRSA Decoding
IRSA[3:0]
DESCRIPTION
Write IRSD[3:0] to DHR[3:0] (Data Hold register)
Write IRSD[3:0] to DHR[7:4] (Data Hold register)
0000
0001
0010
0011
0100
0101
Write IRSD[3:0] to DHR[11:8] (Data Hold register)
Write IRSD[3:0] to DHR[15:12] (Data Hold register)
Reserved
Reserved
Write IRSD[3:0] to ICRA[3:0] or IEEA[3:0] (Internal Calibration register address or internal EEPROM address
nibble 0)
0110
0111
1000
Write IRSD[3:0] to IEEA[7:4] (internal EEPROM address, nibble 1)
Write IRSD[3:0] to IRSP[3:0] or IEEA[9:8] (Interface register set pointer where IRSP[1:0] is IEEA[9:8])
Write IRSD[3:0] to CRIL[3:0] (Command register to internal logic)
Write IRSD[3:0] to ATIM[3:0] (analog timeout value on read)
Write IRSD[3:0] to ALOC[3:0] (analog location)
1001
1010
1011
1100 to 1110
1111
Reserved
Write IRSD[3:0] = 1111bin to relearn the baud rate
and stored in the upper 3 bits of EEPROM location
161hex (EEPROM upper configuration byte).
ommended setting procedure for the Configuration reg-
ister CLK bits is, therefore, as follows. (Use a minimum
baud rate of 9600 during the setting procedure to pre-
vent potential overflow of the MAX1455 baud rate
counter with clock values near maximum.)
The MAX1455 internal clock controls timing functions,
including the signal path gain, DAC functions, and com-
munications. It is recommended that, while in digital
mode, the Configuration register CLK bits be assigned
the values contained in EEPROM (upper configuration
byte). The 3 CLK bits represent a two’s-complement
number with a nominal clock adjustment of 9% per bit.
Table 12 shows the codes and adjustment available.
The following example is based on a required CLK
code of 010 binary:
1) Read the CLK bits (3MSBs) from EEPROM location
161hex. CLK = 010 binary.
2) Set the CLK bits in the Configuration register to 001
binary.
Any change to the CLK bit values contained in the
Configuration register must be followed by the
MAX1455 baud rate learning sequence (reinitialize and
initialize commands). To maximize the robustness of
the communication system during clock resetting only,
change the CLK bits by 1LSB value at a time. The rec-
3) Send the reinitialize command, followed by the ini-
tialize (baud rate learning) command.
4) Set the CLK bits in the Configuration register to 010
binary.
______________________________________________________________________________________ 15
Low-Cost Automotive Sensor Signal
Conditioner
Table 10. CRIL Command Codes
CRIL[3:0]
0000
NAME
LdICR
EEPW
ERASE
RdICR
RdEEP
RdIRS
DESCRIPTION
Load Internal Calibration register at address given in ICRA with data from DHR[15:0].
EEPROM write of 8 data bits from DHR[7:0] to address location pointed by IEEA [9:0].
Erase all of EEPROM (all bytes equal FFhex).
0001
0010
0011
Read Internal Calibration register as pointed to by ICRA and load data into DHR[15:0].
Read internal EEPROM location and load data into DHR[7:0] pointed by IEEA [9:0].
Read Interface register set pointer IRSP[3:0]. See Table 11.
0100
0101
Output the multiplexed analog signal onto OUT. The analog location is specified in ALOC[3:0]
(Table 13) and the duration (in byte times) that the signal is asserted onto the pin is specified in
ATIM[3:0] (Table 14).
0110
0111
RdAlg
Erases the page of the EEPROM as pointed by IEEA[9:6]. There are 64 bytes per page and thus 12
pages in the EEPROM.
PageErase
Reserved
1000 to
1111
Reserved.
5) Send the reinitialize command, followed by the ini-
tialize (baud rate learning) command.
To erase a page in EEPROM (PageErase command):
First load the required page number (Table 1) into the
IRS location IEEA[3:0]. Then send a CRIL PageErase
command (79hex).
The frequency of the internal oscillator can be checked
at any time by reading the value of BITCLK[7:0]. This 8-
bit number represents the number of internal oscillator
cycles corresponding to 1 cycle (1 bit time) of the com-
munications baud rate.
To write a byte to EEPROM: Load IRS locations
IEEA[9:8], IEEA[7:4], and IEEA[3:0] with the byte
address (Address[9:0]). Load IRS locations DHR[7:4]
and DHR[3:0] with the 8 data bits to be written
(Data[7:0]). Send the EEPROM WRITE command to
CRIL (19hex).
Erasing and Writing to the EEPROM
The internal EEPROM must be erased (bytes set to
FFhex) prior to programming the desired contents. The
MAX1455 is supplied in a nominally erased state
except byte 161hex and byte 16Bhex. The 3MSBs of
byte 161hex contain the internal oscillator calibration
setting. Byte 16Bhex is set to 00hex to allow serial com-
munication regardless of the UNLOCK status.
To read a byte from EEPROM:
1) Load IRS locations IEEA[9:8], IEEA[7:4], and
IEEA[3:0] with the byte address (Address[9:0]).
2) Send a READ EEPROM command to the CRIL reg-
ister (49hex); this loads the required EEPROM byte
into DHR[7:0].
When erasing the EEPROM, first save the 3MSBs of
byte 161hex. Following erasure, these 3 bits must be
rewritten, together with the Secure-Lock byte value of
00hex. Failure to do this may cause the part to stop
communicating. Do not remove power from the
device before rewriting these values.
3) Load IRS location IRSP[3:0] with 00hex (return
DHR[7:0]).
4) Send the READ IRSP command to the CRIL register
(59hex).
The internal EEPROM can be entirely erased with the
ERASE command or partially erased with the
PageErase command (Table 10). It is necessary to wait
7.1ms after issuing an erase or PageErase command.
Any attempt to communicate with the part or to interrupt
power before 7.1ms have elapsed may produce inde-
terminate states within the EEPROM.
Multiplexed Analog Output
The MAX1455 provides the facility to output analog sig-
nals while in digital mode through the read analog
(RdAlg) command. One byte time after receiving the
RdAlg command, the internal analog signal determined
by the ALOC[3:0] register (Table 13) is multiplexed to
the MAX1455 OUT. The signal remains connected to
OUT for the duration set by the ATIM[3:0] register. The
16 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
The MAX1455 DIO is three-state for the duration that
the analog output is active. This is to allow OUT and
Table 11. IRSP Decode
IRSP[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
RETURNED VALUE
DIO to be connected in parallel. When DIO and OUT
are connected in parallel, the host computer must also
three-state its communications connection to the
MAX1455. This requirement produces periods when all
connections to the DIO are three-stated simultaneously,
making it necessary to have a weak pullup resistor
applied to DIO during these periods.
DHR[7:0]
DHR[15:8]
IEEA[7:4], ICRA[3:0] concatenated
CRIL[3:0], IRSP[3:0] concatenated
ALOC[3:0], ATIM[3:0] concatenated
IEEA[7:0] EEPROM address byte
IEED[7:0] EEPROM data byte
Temp-Index[7:0]
A continuous output mode is available for the analog
output and is selected by setting ATIM[3:0] to Fhex.
This mode may only be used when DIO and OUT are
separate. While in this mode and following receipt of
the RdAlg command, or any other command, DIO
three-states for a period of 32,769 byte times. Once this
period has elapsed, DIO enters receive mode and
accepts further command inputs. The analog output is
always active while in continuous mode.
BitClock[7:0]
Reserved. Internal flash test data.
Note: The internal analog signals are not buffered
when connected to OUT. Any loading of OUT while one
of these internal signals is being measured is likely to
produce measurement errors. Do not load OUT when
reading internal signals such as BDR, FSOTC, etc.
11001010 (CAhex). This can be used to
test communication.
1010-1111
Table 12. CLK Code (3MSBs of
Configuration Register)
Communication Command Examples
A selection of examples of the command sequences for
various functions within the MAX1455 follows.
CLK CODE (BIN)
CLOCK ADJUSTMENT (%)
011
010
001
000
111
110
101
+27
+18
+9
0
Example 1. Change the baud rate setting and check
communications. If the communication with the
MAX1455 is lost due to a system baud rate change
before sending the reinitialization command, apply a
power reset to guarantee the initialization condition.
-9
COMMAND
ACTION
Reinitialize part ready for baud rate learning.
Change system baud rate to new value.
Learn baud rate.
-18
-27
FFhex
01hex
F8hex
59hex
ATIM function uses the communication baud rate as a
timing basis. See Table 14 for details. At the end of the
period determined by ATIM[3:0], the analog signal is
disconnected from the analog output and OUT
resumes a three-state condition. The MAX1455 can
receive further commands on DIO 1 byte after resum-
ing a three-state condition on OUT. Figure 6 shows the
timing of this scheme.
Load 15 (Fhex) to IRSP[3:0] register.
Read IRS.
Host computer must be ready to receive
data on the serial line within 1 (baud rate)
byte time of sending the Read IRS
command. The MAX1455 returns CAhex.
(IRSP values of 10 to 15 are configured to
return CAhex for communication checking
purposes.)
______________________________________________________________________________________ 17
Low-Cost Automotive Sensor Signal
Conditioner
Example 2. Read the lookup table pointer (Temp-
Index).
Example 4. Write 8C40hex to the FSODAC register.
COMMAND
00hex
ACTION
COMMAND
78hex
ACTION
Load 7 to IRSP[3:0] register.
Read IRS.
Load 0 hex to the DHR[3:0] register.
Load 4 hex to the DHR[7:4] register.
Load C hex to the DHR[11:8] register.
Load 8 hex to the DHR[15:12] register.
Load 3 (FSODAC) to the ICRA[3:0] register.
Ld ICR.
41hex
59hex
C2hex
83hex
Host ready to receive data within 1 byte time
of sending the Read IRS command. The
MAX1455 returns the current Temp-Index
pointer value.
36hex
09hex
8C40 hex is written to the FSODAC register.
Example 3. Enable BDR measurement on OUT pin for
3.4s duration with 9600 baud rate.
Example 5. Write 8C40hex to the FSODAC lookup
table location at Temp-Index 40. This example uses
the Page Erase command to clear the relevant section
of the EEPROM and assumes that none of the existing
data in that section is required to be kept.
COMMAND
ACTION
Load 1 (BDR measurement) to ALOC[3:0]
register.
1Bhex
COMMAND
A6hex
ACTION
12
✕
Load 12 to the ATIM[3:0] register: (2 +1)
CAhex
69hex
Load Ahex (page number corresponding to
EEPROM locations 280hex and 281hex) to
the IEEA[3:0] register.
8/9600 = 3.4s.
RdAlg.
The DIO pin is three-stated and the OUT pin
is connected internally to the BDR pin for a
duration of approximately 3.4s.
79hex
Page Erase command.
Wait 7.1ms before sending any further
commands.
06hex
87hex
Load 0hex to the IEEA[3:0] register.
Load 8hex to the IEEA[7:4] register.
Load 2hex to the IEEA[9:8] (IRSP[3:0])
register.
28hex
00hex
41hex
Load 0hex to the DHR[3:0] register.
Load 4hex to the DHR[7:4] register.
Write EEPROM. 40hex is loaded to EEPROM
address 280hex, which is the low byte
location corresponding to a Temp-Index
pointer value of 40.
19hex
Load 1 to the IEEA[3:0] register. IEEA[7:4]
and IEEA[9:8] already contain 8 and 2,
respectively.
16hex
C0hex
81hex
Load Chex to the DHR[3:0] register.
Load 8hex to the DHR[7:4] register.
Write EEPROM. 8Chex is loaded to
EEPROM address 281hex, which is the high
byte location corresponding to a Temp-
Index pointer value of 40.
19hex
18 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Table 13. ALOC Definition
ALOC[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
ANALOG SIGNAL
OUT
DESCRIPTION
PGA Output
BDR
Bridge Drive
ISRC
Bridge Drive Current Setting
Internal Positive Supply
Internal Ground
VDD
VSS
CLIP-TOP
CLIP-BOTTOM
FSODAC
FSOTCDAC
ODAC
Clip Voltage High Value
Clip Voltage Low Value
Full-Scale Output DAC
Full-Scale Output TC DAC
Offset DAC
OTCDAC
VREF
Offset TC DAC
Bandgap Reference Voltage (nominally 1.25V)
Internal Test Node
VPTATP
VPTATM
INP
Internal Test Node
Sensor’s Positive Input
INM
Sensor’s Negative Input
WEAK PULLUP
REQUIRED
WEAK PULLUP
REQUIRED
ATIM
2
+ 1 BYTE TIMES
DATA
OUT
0
1 1 1 1 1 0 1 0 0 1 0 1 1
1 1 1 1 1 1 1 1 1 X X X X X X X X X X X X 1 1 1 1 1 1 1 1 0 XX
XX
HIGH-Z
HIGH-Z
VALID OUTPUT
HIGH-Z
DIO
RECEIVE
RECEIVE
HIGH-Z
HOST
TRANSMIT
TRANSMIT
Figure 6. Analog Output Timing
______________________________________________________________________________________ 19
Low-Cost Automotive Sensor Signal
Conditioner
Table 14. ATIM Definition
ATIM[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
DURATION OF ANALOG SIGNAL SPECIFIED IN BYTE TIMES (8-BIT TIME)
0
✕
2 + 1 = 2 byte times, i.e., (2 8) / baud rate
21 + 1 = 3 byte times
22 + 1 = 5 byte times
23 + 1 = 9 byte times
24 + 1 = 17 byte times
25 + 1 = 33 byte times
26 + 1 = 65 byte times
27 + 1 = 129 byte times
28 + 1 = 257 byte times
29 + 1 = 513 byte times
210 + 1 = 1025 byte times
211 + 1 = 2049 byte times
212 + 1 = 4097 byte times
213 + 1 = 8193 byte times
214 + 1 = 16,385 byte times
In this mode, OUT is continuous; however, DIO accepts commands after 32,769 byte times. Do not parallel
connect DIO to OUT.
1111
Table 15. ICRA Decode
ICRA[3:0]
0000
NAME
CONFIG
ODAC
DESCRIPTION
Configuration register
0001
Offset DAC register
0010
OTCDAC
FSODAC
FSOTCDAC
Offset temperature coefficient DAC register
Full-scale output DAC register
0011
0100
Full-scale output temperature coefficient DAC register
Reserved. Do not write to this location (EEPROM test).
0101
0110 to
1111
Reserved. Do not write to this location.
zero and full span) and two temperatures. More test
pressures and temperatures result in greater accuracy.
A typical compensation procedure can be summarized
as follows:
Sensor Compensation Overview
Compensation requires an examination of the sensor
performance over the operating pressure and tempera-
ture range. Use a minimum of two test pressures (e.g.,
20 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
DIO[1:N]
DIGITAL
DION
DIO2
DIO1
MULTIPLEXER
MODULE 1
MODULE 2
MODULE N
DATA
DATA
V
V
OUT
V
OUT
OUT
V
V
SS
V
V
SS
V
V
SS
DD
DD
DD
+5V
V
OUT
DVM
TEST OVEN
Figure 7. Automated Test System Concept
Table 16. Effects of Compensation
TYPICAL UNCOMPENSATED INPUT (SENSOR)
TYPICAL COMPENSATED TRANSDUCER OUTPUT
Offset…………………..…….…………………………. 100% FSO
FSO…………………………….………………....1mV/V to 40mV/V
OUT..…….………………………………Ratiometric to V at 5.0V
DD
Offset at +25°C……………………………………0.500V 200µV
FSO at +25°C……………………………………...4.000V 200µV
Offset Accuracy over Temp. Range….…….. 4mV ( 0.1% FSO)
FSO Accuracy over Temp. Range………….. 4mV ( 0.1% FSO)
Offset TC…………………………………………………...20% FSO
Offset TC Nonlinearity…..………………………………….4% FSO
FSOTC…………………………..………………………..-20% FSO
FSOTC Nonlinearity…..……..…………………………….5% FSO
Temperature Range..….….……………………..-40°C to +125°C
Set Reference Temperature (e.g., 25°C):
•
•
Calibrate the output offset and FSO of the transduc-
er using the ODAC and FSODAC, respectively.
•
Initialize each transducer by loading its respective
register with default coefficients (e.g., based on
mean values of offset, FSO, and bridge resistance)
to prevent overload of the MAX1455. The internal
calibration registers are addressed in ICRA[3:0]
and decoded as shown in Table 15.
Store calibration data in the test computer or
MAX1455 EEPROM user memory.
Set Next Test Temperature:
•
•
•
Calibrate offset and FSO using the ODAC and
FSODAC, respectively.
•
Set the initial bridge voltage (with the FSODAC) to
half of the supply voltage. Measure the bridge volt-
age using the BDR or OUT pins, or calculate based
on measurements.
Store calibration data in the test computer or
MAX1455 EEPROM user memory.
Calculate the correction coefficients.
______________________________________________________________________________________ 21
Low-Cost Automotive Sensor Signal
Conditioner
UNCOMPENSATED SENSOR
TEMPERATURE ERROR
RAW SENSOR OUTPUT
(T = +25°C)
A
30
20
80
FSO
OFFSET
60
40
10
0
20
0
-10
-20
0
20
40
60
80
100
-50
0
50
TEMPERATURE (°C)
100
150
PRESSURE (kps)
COMPENSATED TRANSDUCER
(T = +25°C)
A
COMPENSATED TRANSDUCER ERROR
5
4
3
2
1
0
0.15
0.10
0.05
0
-0.05
-0.10
-0.15
FSO
OFFSET
-50
0
50
TEMPERATURE (°C)
150
0
20
40
60
80
100
100
PRESSURE (kps)
Figure 8. Comparison of an Uncalibrated Sensor and a Calibrated Transducer
•
•
Download correction coefficients to EEPROM.
Perform a final test.
MAX1455 evaluation kit (EV kit). First-time users of the
MAX1455 are strongly encouraged to use this kit.
The EV kit is designed to facilitate manual programming
of the MAX1455 with a sensor. It includes the following:
Sensor Calibration and
Compensation Example
1) Evaluation board with or without a silicon pressure
The MAX1455 temperature compensation design cor-
rects both sensor and IC temperature errors. This
enables the MAX1455 to provide temperature compen-
sation approaching the inherent repeatability of the
sensor. An example of the MAX1455’s capabilities is
shown in Figure 8. Table 16 lists the effects of compen-
sation.
sensor, ready for customer evaluation.
2) Design/applications manual. This manual was
developed for test engineers familiar with data
acquisition of sensor data and provides sensor
compensation algorithms and test procedures.
3) MAX1455 communication software, which enables
programming of the MAX1455 from a computer key-
board (IBM compatible), one module at a time.
A MAX1455 and a repeatable piezoresistive sensor with
an initial offset of 16.4mV and a span of 55.8mV were
converted into a compensated transducer with an offset
of 0.5000V and a span of 4.0000V. Nonlinear sensor
offset and FSO temperature errors, which were on the
order of 20% to 30% FSO, were reduced to under
0.1% FSO. Figure 8 shows the output of the uncom-
pensated sensor and the output of the compensated
transducer. Six temperature points were used to obtain
this result.
4) Interface adapter, which allows the connection of
the evaluation board to a PC serial port.
Chip Information
TRANSISTOR COUNT: 62,242
PROCESS: CMOS
SUBSTRATE CONNECTED TO: V
SS
MAX1455 Evaluation Kit
To expedite the development of MAX1455-based
transducers and test systems, Maxim has produced the
22 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Detailed Functional Diagram
EEPROM
TEST 1
TEST 2
TEST 3
TEST 4
(LOOKUP PLUS CONFIGURATION DATA)
V
DD
EEPROM ADDRESS
USAGE
000H + 001H
OFFSET DAC LOOKUP TABLE
V
DD
✕
(176 16 BITS)
:
16 BIT
15EH + 15FH
160H + 161H
162H + 163H
164H + 165H
166H + 167H
168H + 169H
16AH + 16BH
16CH + 16DH
FSO
DAC
V
V
DD1
CONFIGURATION REGISTER SHADOW
RESERVED
V
SS
OFFSET TC REGISTER SHADOW
RESERVED
SS
FSOTC REGISTER SHADOW
CONTROL LOCATION REGISTER
USER STORAGE (52 BYTES)
V
DD
SS
16 BIT
OFFSET
DAC
:
R
ISRC
R
STC
75kΩ
75kΩ
19EH + 19FH
1A0H + 1A1H
:
V
V
DD2
FSO DAC LOOKUP TABLE
✕
(176 16 BITS)
V
SS
2FEH + 2FFH
V
DD
8-BIT
LOOKUP
ADDRESS
BANDGAP
TEMP
SENSOR
1
∑∆
16 BIT
BDR
FSOTC
DAC
UNLOCK
DIO
DIGITAL
INTERFACE
V
SS
INP
CLIP-HIGH
PHASE
REVERSAL
MUX
V
SS
FSOTC REGISTER
PGA BANDWIDTH ≈
3kHz 10%
DAC
✕
MUX
24
PGA
MUX
∑
∑
OUT
DAC
INM
CLIP-LOW
INPUT-REFERRED OFFSET
(COARSE OFFSET)
AMP-
PROGRAMMABLE GAIN STAGE
V
SS
1
PGA (3:0) PGA GAIN TOTAL GAIN
IRO (3, 2:0) OFFSET (mV)
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
39
52
1,111
1,110
1,101
1,100
1,011
1,010
1,001
1,000
0,000
0,001
0,010
0,011
0,100
0,101
0,110
0,111
63
54
45
36
27
18
9
AMPOUT
65
16 BIT
78
OFFSET
TC DAC
AMP+
91
104
117
130
143
156
169
182
195
208
221
234
V
OTC REGISTER
SS
0
UNCOMMITTED OP AMP
0
*INPUT-REFERRED
OFFSET VALUE IS
PROPORTIONAL TO V
VALUES GIVEN ARE FOR
= +5V.
-9
PARAMETER
I/P RANGE
VALUE
TO V
-18
-27
-36
-45
-54
-63
V
SS
DD
.
DD
I/P OFFSET
20mV
V
DD
O/P RANGE
NO LOAD
1mA LOAD
V
V
, V
SS DD
0.01V
0.25V
SS DD
, V
UNITY GBW
10MHz TYPICAL
PGA BANDWIDTH ≈ 3kHz 10%
______________________________________________________________________________________ 23
Low-Cost Automotive Sensor Signal
Conditioner
Package Information
24 ______________________________________________________________________________________
Low-Cost Automotive Sensor Signal
Conditioner
Package Information (continued)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 25
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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