3–338
Motorola Sensor Device Data
For More Information On This Product,
Go to: www.freescale.com
The Motorola MPX2010 (see Table 1) is a calibrated and
temperature compensated, 10 kPa (full–scale), pressure
sensor device. The data sheet specifies a full–scale output of
25 mV at a 10 V supply voltage, for an applied pressure of 10
kPa. This same device can be pulsed at 40 V at a 10%
duty–cycle and produce either 100 mV for the same 10 kPa
pressure or 25 mV for only 2.5 kPa of pressure. This technique
allows a four–fold increase in the signal level for the rated
full–scale pressure of 10 kPa or the ability to maintain the
same signal level for a pressure that is four times lower (2.5
kPa).
Although the idea is relatively simple, the key to providing a
low–cost smart sensing solution is in both the hardware and
software implementation of this system. In the case of the
micropower application, having a “stand–alone” analog
sensing solution was a key criteria. As such, this design used
micropower op–amps, analog CMOS switches, gated timers
(one to control pulsed sensor excitation and one to control
sample–and–hold
function),
sample–and–hold circuitry. The effect was a very low–current
drain, micropower sensor solution. Since low–power, rather
than low–pressure, was the driving design goal, errors
induced by power supply variation, temperature drift, and
device–to–device tolerances were not critical. Not that these
issues are not important for all applications, but for
low–pressure sensing, even small temperature drifts, device
parameter tolerances, and power supply variations cause
significant errors as a percentage of the sensor output signal.
It
should
be
apparent
pulsing/sample–and–hold” system architecture can be
equally well employed to pulse at higher voltages for
and
capacitive
that
the
“gated–timer
increased sensitivity. However, a low–cost MCU can also
accomplish the functions of providing a control pulse to a
switching circuit (for the pulsed sensor excitation) and
affecting a synchronized sample–and–hold feature via
software control of an on–chip A/D converter. In addition, the
MCU has the capability to implement other “smart” features
that can lend the additional required accuracy and
functionality desired for many low–pressure sensing
applications. The system design intended for low–pressure
applications, as well as the performance–enhancing features
of pulsed excitation for increased sensitivity, signal averaging,
software calibration, and software power supply rejection are
presented.
The
added
communications capability and serial digital output flexibility
are also discussed.
Of course, these features lead to increased performance at
conventional, or even high–pressure ranges. Nonetheless,
these features have been developed in the context of
low–pressure sensing where the performance benefits are a
requisite of the application. Also, driving acceptance of this
system technology is a much easier task when coupled to
providing a sensing capability and level of functionality that is
otherwise not available in the industry today. Who would have
suspected that a viable smart sensing technology would have
resulted from the pursuit of addressing the low–pressure
sensing market Significant pieces of this system solution are
protected intellectual property. Motorola holds several key
patents on using pulsed excitation for semiconductor sensors
and has filed several others regarding other portions and
future enhancements to this technology.
functionality
of
intelligent
Table 1. MPX2010 Operating Characteristics
(Supply Voltage = 10 Vdc, TA = 25
°
C unless otherwise noted)
Characteristic
Min
Typ
Max
Unit
Pressure Range
0
—
10
kPa
Supply Voltage
—
10
16
Vdc
Supply Current
—
6.0
—
mAdc
Full Scale Span (FSS)
24
25
26
mV
Zero–Pressure Offset
–1.0
—
1.0
mV
Sensitivity
—
2.5
—
mV/kPa
Linearity
–1.0
—
1.0
%VFSS
%VFSS
%VFSS
%VFSS
mV
Pressure Hysteresis (0 to 10 kPa)
—
±
0.1
—
Temperature Hysteresis (–40
°
C to +125
°
C)
—
±
0.5
—
Temperature Effect on Full Scale Span
–1.0
—
1.0
Temperature Effect on Offset (0
°
C to 85
°
C)
–1.0
—
1.0
Input Impedance
1300
—
2550
Output Impedance
1400
—
3000
Response Time (10% to 90%)
—
1.0
—
ms
Temperature Error Band
0
—
85
°
C
Offset Stability
—
±
0.5
—
%VFSS
F
Freescale Semiconductor, Inc.
n
.