MPX2202
Sensors
Freescale Semiconductor, Inc. 5
Pressure
On-Chip Temperature Compensation and Calibration
Figure 2. Output vs. Pressure Differential
Figure 2 shows the output characteristics of the MPX2202
series at 25C. The output is directly proportional to the
differential pressure and is essentially a straight line.
The effects of temperature on full scale span and offset are
very small and are shown under Operating Characteristics.
Figure 3. Cross Sectional Diagram (not to scale)
Figure 3 illustrates the differential/gauge die in the basic
chip carrier (Case 344). A silicone gel isolates the die surface
and wire bonds from the environment, while allowing the
pressure signal to be transmitted to the silicon diaphragm.
The MPX2202 series pressure sensor operating
characteristics and internal reliability and qualification tests
are based on use of dry air as the pressure media. Media
other than dry air may have adverse effects on sensor
performance and long term reliability. Contact the factory for
information regarding media compatibility in your application.
LINEARITY
Linearity refers to how well a transducer's output follows
the equation: V
out
= V
off
+ sensitivity x P over the operating
pressure range. There are two basic methods for calculating
nonlinearity: (1) end point straight line fit (see Figure 4) or
(2) a least squares best line fit. While a least squares fit gives
the “best case” linearity error (lower numerical value), the
calculations required are burdensome.
Conversely, an end point fit will give the “worst case” error
(often more desirable in error budget calculations) and the
calculations are more straightforward for the user.
Freescale’s specified pressure sensor linearities are based
on the end point straight line method measured at the
midrange pressure.
Figure 4. Linearity Specification Comparison
Output (mV
DC
)
VS = 10 V
DC
T
A
= 25C
P1 > P2
40
35
30
25
20
15
10
5
0
-5
TYP
MAX
MIN
Span
Range
(TYP)
Offset
(TYP)
0 50 100 150 200kPa
PSI 7.25 14.5 21.75 29
1751257525
Pressure
Lead Frame
Wire Bond
Differential/Gauge
Die
Silicone Gel
Die Coat
Differential/Gauge
P2
Die
Bond
Epoxy
Case
Stainless Steel
Metal Cover
P1
Silicone Gel
Die Coat
Absolute
Die
P1
Metal Cover
Epoxy
Case
Absolute Element
P2
Lead Frame
Wire Bond
Die
Bond
Stainless Steel
Element
Least
Square
Deviation
Relative Voltage Output
Pressure (% Full Scale)
0
50 100
End Point Straight
Line Fit
Exaggerated
Performance
Curve
Least Squares Fit
Straight Line
Deviation
Offset
