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| MAX1457 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – 0.1%-Accurate Signal Conditioner for Piezoresistive Sensor Compensation | |||
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0.1%-Accurate Signal Conditioner
for Piezoresistive Sensor Compensation
+5V
RSTC
RISRC
50k
RLIN (OPTIONAL)
CURRENT
ISRC
SOURCE
VDD
VDD
BIAS
GENERATOR
NBIAS
RBIAS
400k
0.1µF
0.1µF
0.1µF
SENSOR
+5V
EEPROM
93C66 SO-8
VDD
CS
CLK
ORG
DI
VSS
DO
0.1µF
BDRIVE
INP
INM
0.1µF
AGND
+5V
5k*
MCS
ECS
ECLK
EDI
EDO
LINDACREF
AMP+
AMP-
PGA
VDD
VSS
12-BIT ADC
SERIAL
EEPROM
INTERFACE
VDD
MAX1457
OSCILLATOR
FADJ
FOUT
VOUT
LINDAC
FSOTCDAC
OTCDAC
OFSTDAC
FSODAC
A = 1 LINOUT
A = 1 FSOTCOUT
VBDRIVE
A = 1 VBBUF
OP AMP
AMPOUT
VSS
0.1µF
ROSC
1.5M
VOUT
5 x 0.1µF
*OPTIONAL PULL-UP RESISTOR
Figure 5. Basic Ratiometric Output Configuration
Sensor Compensation Overview
Compensation requires an examination of the sensor
performance over the operating pressure and tempera-
ture range. Use two test pressures (e.g., zero and full-
span) and two temperatures. More test pressures and
temperatures will result in greater accuracy. A simple
compensation procedure can be summarized as follows:
Set reference temperature (e.g., +25°C):
1) Initialize each transducer by loading its EEPROM with
default coefficients (e.g., based on mean values of
offset, FSO, and bridge resistance) to prevent gross
overload of the MAX1457.
2) Set the initial bridge voltage (with the FSO DAC) to
half the supply voltage. The bridge voltage can be
measured by the MAX1457 and returned to the test
computer via the serial interface or by using the sys-
tem digital voltmeter to measure the voltage on either
BDRIVE or VBBUF.
3) Calibrate the transducerâs output offset and FSO
using the OFFSET and FSO DACs, respectively.
4) Store calibration data in the test computer.
Set next test temperature:
5) Calibrate offset and FSO using the OFFSET TC and
FSO TC DACs, respectively.
6) Store calibration data in the test computer.
Repeat steps 5 and 6 for each required test tempera-
ture.
8 _______________________________________________________________________________________
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