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MAX1450 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – Low-Cost, 1%-Accurate Signal Conditioner for Piezoresistive Sensors
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Low-Cost, 1%-Accurate Signal Conditioner
for Piezoresistive Sensors
5) Set VFSOTRIM = VBIDEAL(25°C). Adjust RISRC until
VBBUF = VBIDEAL(25°C).
6) Readjust VOFFSET until the offset voltage is 0.5V (see
OFFSET Calibration section).
FSO TC Compensation
Correct linear span TC by connecting BBUF to ISRC
through a resistor (RSTC). The value of RSTC depends
on the required correction coefficient, which is sensor
dependent, but typically around 100kΩ for most silicon
PRTs. The following procedure results in FSO TC cali-
bration:
1) Measure the full-span output at T2.
2) Use the equation from Step 4 of the FSO Calibration
section to determine VBIDEAL(T2). While at T2, adjust
RSTC until VBBUF = VBIDEAL(T2).
3) Do not adjust VOFFSET or VOFFTC.
OFFSET TC Compensation
Connect OFFTC to a resistor divider between BBUF
and VSS. The divided-down VBBUF is then fed into
OFFTC and the appropriate polarity (designating
whether VOFFTC should be added or subtracted from
the PGA output) is selected with SOTC.
1) At T2, remeasure the offset at VOUT.
2) Use the following equation to determine the magni-
tude of VOFFTC(T2), and adjust ROTCA accordingly. If
VOFFTC is negative, connect SOTC to VSS. If VOFFTC
is positive, connect SOTC to VDD. After OTC calibra-
tion, the output may be saturated; correct this condi-
tion during OFFSET calibration. In most cases
Current OFFTC will be 0. However, if a coarse
OFFTC adjustment was performed, the coefficient
must be inserted in the equation below.
( ) VOFFTC =
VOFFSET(T1) − VOFFSET(T2)
VBDRIVE(T1) − VBDRIVE(T2) x 1.15
+ Current OFFTC
where Current OFFTC is the voltage at pin OFFTC.
Note that the magnitude of VOFFTC is directly propor-
tional to the gain of the PGA. Therefore, if the PGA gain
changes after performing the offset TC calibration, the
offset TC must be recalibrated.
VDD
RFSOB
RFSOA
0.1µF
SENSOR
RSTC
VDD
RISRC
RLIN (OPTIONAL)
FSOTRIM
VDD
CURRENT
SOURCE
ISRC VDD
BDRIVE
INP
INM
PGA
A2
A1
A0
OUT
SOTC
SOFF
OFFTC
OFFSET
MAX1450
A = 1 BBUF
VSS
0.1µF
VDD
OUT
0.1µF
VDD
ROTCB
VDD
ROTCA
ROFFB
ROFFA
Figure 4. Basic Ratiometric Output Configuration
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