
3
Motorola Sensor Device Data
LINEARITY
Linearity refers to how well a transducer’s output follows
the equation: Vout = Voff + sensitivity x P over the operating
pressure range. There are two basic methods for calculating
nonlinearity: (1) end point straight line fit or (2) a least
squares best line fit (see Figure 3). 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. Motorola’s
specified pressure sensor linearities are based on the end
point straight line method measured at the midrange
pressure.
Figure 2. Linearity Specification Comparison
LEAST
SQUARE
DEVIATION
R
PRESSURE (% FULLSCALE)
0
50
100
END POINT
STRAIGHT LINE FIT
EXAGGERATED
PERFORMANCE
CURVE
LEAST SQUARES FIT
STRAIGHT LINE
DEVIATION
OFFSET
ON–CHIP TEMPERATURE COMPENSATION and CALIBRATION
Figure 3 shows the output characteristics of the
MPX2700A 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 Characteris-
tics.
Figure 3. Output versus Pressure Differential
Figure 4. Cross–Section of Differential Pressure
Sensor Die in Its Basic Package (Not to Scale)
ééééééééééé
SILICONE
DIE COAT
DIE
ééééééééééé
ééééééééééé
ééééééééééé
ééééééééééé
ééééééééééé
ééééééééééé
THERMOPLASTIC CASE
WIRE BOND
LEAD
FRAME
METAL COVER
RTV DIE
BOND
P2
50
40
30
20
10
–5
20
140
40
280
60
420
100
700
O
SPAN
RANGE
(TYP)
OFFSET
PSI
kPa
VS = 10 V
TA = 25
°
C
P1 > P2
MAX
TYP
MIN
0
80
560
Figure 4 shows the cross section of the Motorola MPX
pressure sensor die in the chip carrier package. A silicone
gel isolates the die surface and wire bonds from harsh
environments, while allowing the pressure signal to be
transmitted to the silicon diaphragm. MPX2700A series
pressure sensor operating characteristics and internal reli-
ability 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.