MPXM2102AS datasheet(539/670 Pages) MOTOROLA

539 / 670 page

AN1668

3–393

Motorola Sensor Device Data

www.motorola.com/semiconductors

When designing a system based on the MPX2010, it is

important to take into account errors due to parametric varia-

tion of the sensor (i.e. offset calibration, span calibration, TcS,

TcO), power supply and the inherent errors of the amplification

circuit. The offset and span errors greatly determines the reso-

lution of the system (which adds to the system error). Even

though the system offset error can be nulled out by auto–zero-

ing, these errors must be accounted for when setting the sys-

tem gain (see AN1556 for more details). This forces the total

span of the system to be smaller, because we must reserve an

extra headroom from the total span to account for amplifier

and A/D variations (i.e. amp. sat. voltage, power supply varia-

tion, A/D quantization error, and gain errors ). If these errors

are not accounted for, it could, for example, result in non–

linearity errors if the sensor span or offset error causes the

amplified output of the sensor to reach the saturation voltage

of the amplifier.

As an example, a MPX2010 sensor system is designed

which has a range of 600 mmH2O FS range with a +/– 5 % FS

RMS error. The system uses a +5 V +/– 5% linear regulated

power supply, a MC33272 dual op–amp and a 1% resistors.

Table 3 shows the resulting specification and component

values for the system based on MPX2010 sensor.

Table 3. MPX2010 Sensor System Values

MPX2010 Sensor Design

Parameter

Description

Value

Units

Vcc

Reg Power Supply

Differential Gain

Gain

433

V/V

Vout_FS

Full Scale Span

3.02

Vref

Offset Reference

0.66

Parts List

U1A,U1B

MC33272 Op–amp

Gain Resistor

39.2K

Ohms

Gain Resistor

90.9

Ohms

Gain Resistor

909

Ohms

Gain Resistor

392K

Ohms

R + S1

Level Shift Resistor

Ohms

R + S2

Level Shift Resistor

150

Ohms

MPX2010

Table 4. Performance Comparison between MPX2010 and MPXV4006G Solution

MPX2010 Solution Error

(FS = 600 mmH2O)

MPXV4006G Solution Error

(FS = 612 mmH2O)

Error Contribution

+/– % FS

+/– mmH2O

+/– % FS

+/– mmH2O

Max Sensor Error

7.19

3.00

System Resolution (A/D + Amplification)

1.30

0.80

System Error (Sensor + A/D + Amplification)

7.3

3.10

System Error with Auto–Zero

4.6

t19

Note that the error due to system resolution is higher for the

MPX2010 solution (+/– 2 bit A/D accuracy). This is because

the MPX2010 span is limited as discussed above. Also, this

accuracy assumes that the amplifier does not induce signifi-

cant errors. As noted MPXV4006G sensor has better overall

accuracy. The system resolution is very good because of its

large span (4.6 V versus 3.0 V typical).

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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