MPX700 SERIES

3

Motorola Sensor Device Data

TEMPERATURE COMPENSATION

Figure 2 shows the typical output characteristics of the

MPX700 series over temperature.

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

or by designing your system using the MPX2700 series

sensors.

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 Diagrams (not to scale)

OFFSET

(VOFF)

70

50

40

30

20

10

0

0

MAX

POP

SPAN

(VFSS)

PRESSURE (kPA)

ACTUAL

THEORETICAL

LINEARITY

SILICONE GEL

DIE COAT

WIRE BOND

LEAD FRAME

DIFFERENTIAL/GAUGE

DIE

STAINLESS STEEL

METAL COVER

EPOXY

CASE

DIFFERENTIAL/GAUGE ELEMENT

DIE

BOND

SILICONE GEL

DIE COAT

WIRE BOND

LEAD FRAME

ABSOLUTE

DIE

STAINLESS STEEL

METAL COVER

EPOXY

CASE

DIE

BOND

ABSOLUTE ELEMENT

P1

P2

P1

P2

80

70

60

50

40

30

20

10

0

0

60

PSI

700

560

420

280

140

kPa

PRESSURE DIFFERENTIAL

20

100

80

SPAN

RANGE

(TYP)

OFFSET

(TYP)

MPX700

VS = 3 Vdc

P1 > P2

–40

°C

+25

°C

+ 125

°C

40

Figure 4 illustrates the differential or gauge configuration

in the basic chip carrier (Case 344–15). A silicone gel iso-

lates the die surface and wire bonds from the environment,

while allowing the pressure signal to be transmitted to the sil-

icon diaphragm.

The MPX700 series pressure sensor operating character-

istics 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 re-

garding media compatibility in your application.