MPX2202

Sensors

Freescale Semiconductor

5

Pressure

On-Chip Temperature Compensation and Calibration

Figure 2. Output vs. Pressure Differential

series at 25

°C. 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

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

P1 > P2

40

35

30

25

20

15

10

5

0

-5

TYP

MAX

MIN

Span

Range

(TYP)

Offset

(TYP)

0

50

100

150

200

kPa

PSI

7.25

14.5

21.75

29

175

125

75

25

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

Pressure (% Full Scale)

0

50

100

End Point Straight

Line Fit

Exaggerated

Performance

Curve

Least Squares Fit

Straight Line

Deviation

Offset