
3–287
Motorola Sensor Device Data
For More Information On This Product,
  Go to: www.freescale.com
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
C1
0.2 
μ
F
I
O
G
3
1
2
B+
GND
OUT
C2
0.2
 μ
F
XDCR1
MPX2000 SERIES
SENSOR
1
2
4
3
U1B
MC33272
+
1
4
3
2
–
+
8
6
R1 93.1 k 1%
U1
MC78L08ACP
C2 0.001 
μ
F
R2
750
1%
R4
100
1%
R6
11 k
1%
R5
1.33 k
1%
R7
TRIM
R3
39.2 k
1%
5
7
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.
F
Freescale Semiconductor, Inc.
n
.