allel. The MAX1452 allows for a high degree of flexibili-

ty in system calibration design. This is achieved by use

of single-wire digital communication and three-state

output nodes. Depending upon specific calibration

requirements one may connect all the OUTs in parallel

or connect DIO and OUT on each individual module.

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.,

zero and full-span) and two temperatures. More test

pressures and temperatures will result in greater accu-

racy. A typical compensation procedure can be sum-

marized as follows:

Set reference temperature (e.g., 25°C):

•

Initialize each transducer by loading their respec-

tive registers with default coefficients (e.g., based

on mean values of offset, FSO and bridge resis-

tance) to prevent overload of the MAX1452.

•

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.

•

Calibrate the output offset and FSO of the transduc-

er using the ODAC and FSODAC, respectively.

•

Store calibration data in the test computer or

MAX1452 EEPROM user memory.

Set next test temperature:

•

Calibrate offset and FSO using the ODAC and FSO-

DAC, respectively.

•

Store calibration data in the test computer or

MAX1452 EEPROM user memory.

•

Calculate the correction coefficients.

•

Download correction coefficients to EEPROM.

•

Perform a final test.

Sensor Calibration and

Compensation Example

The MAX1452 temperature compensation design cor-

rects both sensor and IC temperature errors. This

enables the MAX1452 to provide temperature compen-

sation approaching the inherent repeatability of the

sensor. An example of the MAX1452’s capabilities is

shown in Figure 8.

A repeatable piezoresistive sensor with an initial offset

of 16.4mV and a span of 55.8mV was converted into a

compensated transducer (utilizing the piezoresistive

sensor with the MAX1452) 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. The fol-

lowing graphs show the output of the uncompensated

sensor and the output of the compensated transducer.

Six temperature points were used to obtain this result.

MAX1452 Evaluation Kit

To

expedite

the

development

of

MAX1452

based transducers and test systems, Maxim has pro-

duced the MAX1452 evaluation kit (EV kit). First-time

users of the MAX1452 are strongly encouraged to use

this kit.

Low-Cost Precision Sensor

Signal Conditioner

14

______________________________________________________________________________________

DRIVEN BY TESTER

THREE-STATE

NEED WEAK

PULLUP

THREE-STATE

NEED WEAK

PULLUP

1 1 1 1 1 1 1 1

11

11 1 1

11 1

11

1

11

THREE-STATE

TIMES

DIO

OUT

VALID OUT

HIGH IMPEDANCE

Figure 6. Analog Output Timing