MPXM2102AS datasheet(433/670 Pages) MOTOROLA

433 / 670 page

AN1325

3–287

Motorola Sensor Device Data

www.motorola.com/semiconductors

NOTES:

R7 IS NOMINALLY 39.2 k AND SELECTED FOR ZERO PRESSURE VOUT = 0.5 V

FOR MPX2010 SENSORS R1 = 150 k AND R4 = 61.9 OHMS

0.2

µF

B+

GND

OUT

0.2

µF

XDCR1

MPX2000 SERIES

SENSOR

U1B

MC33272

–

R1 93.1 k 1%

MC78L08ACP

C2 0.001

µF

750

100

11 k

1.33 k

TRIM

39.2 k

U2B

MC33272

Figure 4. Sensor Mini Amp

–

PERFORMANCE

Performance differences between the three topologies are

minor. Accuracy is much more dependent upon the quality of

the resistors and amplifiers that are used and less dependent

on which of the three circuits are chosen. For example, input

offset voltage error is essentially the same for all three circuits.

To a first order approximation, it is equal to total gain times the

difference in offset between the two amplifiers that are directly

tied to the sensor.

Errors due to resistor tolerances are

somewhat dependent upon circuit topology. However, they

are much more dependent upon the choice of resistors.

Choosing 1% resistors rather than 5% resistors has a much

larger impact on performance than the minor differences that

result from circuit topology. Assuming a zero pressure offset

adjustment, any of these circuits with an MPX2000 series

sensor, 1% resistors and an MC33274 amplifier results in a

± 5% pressure to voltage translation from 0 to 50° C. Software

calibration can significantly improve these numbers and

eliminate the need for analog trim.

CONCLUSION

Although the classic instrumentation amplifier is the best

known and most frequently used sensor interface amplifier, it

is generally not the optimal choice for inexpensive circuits

made from discrete components. The circuit that is shown in

Figure 4 performs the same interface function with

significantly fewer components, less board space and at a

lower cost. It is generally the preferred interface topology for

MPX2000 series semiconductor pressure sensors.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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