MPX906 SERIES

3

Motorola Sensor Device Data

TEMPERATURE COMPENSATION

Figure 2 shows the output characteristics of the MPX906D

series at 25

°C.

The X–ducer piezoresistive pressure sensor element is a

semiconductor device which gives an electrical output signal

proportional to the pressure applied to the device. This de-

vice uses a unique transverse voltage diffused semiconduc-

tor strain gauge which is sensitive to stresses produced in a

thin silicon diaphragm by the applied pressure.

Because this strain gauge is an integral part of the silicon

diaphragm, there are no temperature effects due to differ-

ences in the thermal expansion of the strain gauge and the

diaphragm, as are often encountered in bonded strain gauge

pressure sensors. However, the properties of the strain

gauge itself are temperature dependent, requiring that the

device be temperature compensated if it is to be used over

an extensive temperature range.

Temperature compensation and offset calibration can be

achieved rather simply with additional resistive components.

Several approaches to external temperature compensa-

tion over both – 40 to +125

°C and 0 to +80°C ranges are

presented in Motorola Applications Note AN840.

LINEARITY

Linearity refers to how well a transducer’s output follows

the equation: Vout = Voff + sensitivity x P over the operating

pressure range (Figure 3). There are two basic methods for

calculating nonlinearity: (1) end point straight line fit or (2) a

least squares best line fit. While a least squares fit gives the

“best case” linearity error (lower numerical value), the cal-

culations 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. Motorola’s

specified pressure sensor linearities are based on the end

point straight line method measured at the midrange

pressure.

Figure 2. Output versus Pressure Differential

Figure 3. Linearity Specification Comparison

Figure 4. Cross–Sectional Diagram (not to scale)

OFFSET

(VOFF)

70

60

50

40

30

20

10

0

0

MAX

POP

SPAN

(VFSS)

PRESSURE (kPA)

ACTUAL

THEORETICAL

LINEARITY

PRESSURE DIFFERENTIAL (mmH20)

5

0

100

200

300

400

0

–10

–5

–15

–20

–25

500

600

VS = 3 Vdc

P2 > P1

SILICONE

DIE COAT

WIRE BOND

LEAD FRAME

DIE

STAINLESS STEEL

METAL COVER

EPOXY CASE

RTV DIE

BOND

P1

P2

PRESSURE (P2) SIDE

AMBIENT (P1) SIDE

25

°C

0

°C

85

°C