MAX1450 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1450

Low-Cost, 1%-Accurate Signal Conditioner for Piezoresistive Sensors

Maxim Integrated 

MAX1450

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 depen-

dent, but typically around 100kΩ for most silicon PRTs.

The following procedure results in FSO TC calibration:

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 adjust-

ment was performed, the coefficient must be inserted

in the equation below.

( ) VOFFTC =

VOFFSET(T1) − VOFFSET(T2)

VBDRIVE(T1) − VBDRIVE(T2) × 1.15

+ Current OFFTC

where Current OFFTC is the voltage at pin OFFTC.

Note that the magnitude of VOFFTC is directly proportional

to the gain of the PGA. Therefore, if the PGA gain chang-

es 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

A2

ISRC VDD

A1

A0

BDRIVE

INP

INM

OUT

PGA

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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