MPXM2102AS datasheet(452/670 Pages) MOTOROLA

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Motorola Sensor Device Data

www.motorola.com/semiconductors

AN1517

Pressure Switch Design with

Semiconductor Pressure Sensors

Prepared by: Eric Jacobsen and Jeff Baum

Sensor Design and Applications Group, Motorola Phoenix, AZ

INTRODUCTION

The Pressure Switch concept is simple, as are the additions

to conventional signal conditioning circuitry required to

provide a pressure threshold (or thresholds) at which the

output switches logic state. This logic–level output may be

input to a microcontroller, drive an LED, control an electronic

switch, etc. The user–programmed threshold (or reference

voltage) determines the pressure at which the output state will

switch.

An additional feature of this minimal component

design is an optional user–defined hysteresis setting that will

eliminate multiple output transitions when the pressure sensor

voltage is comparable to the threshold voltage.

This paper presents the characteristics and design criteria

for each of the major subsystems of the pressure switch

design: the pressure sensor, the signal conditioning (gain)

stage, and the comparator output stage. Additionally, an entire

section will be devoted to comparator circuit topologies which

employ comparator ICs and/or operational amplifiers. A

window comparator design (high and low thresholds) is also

included. This section will discuss the characteristics and

design criteria for each comparator circuit, while evaluating

them in overall performance (i.e., switching speed, logic–level

voltages, etc.).

BASIC SENSOR OPERATION

Motorola’s MPX2000 Series sensors are temperature

compensated and calibrated (i.e., offset and full–scale span

are precision trimmed) pressure transducers. These sensors

are available in full–scale pressure ranges from 10 kPa

(1.5 psi) to 200 kPa (30 psi). Although the specifications (see

Table 1) in the data sheets apply only to a 10 V supply voltage,

the output of these devices is ratiometric with the supply

voltage. For example, at the absolute maximum supply

voltage rating, 16 V, the sensor will produce a differential

output voltage of 64 mV at the rated full–scale pressure of the

given sensor. One exception to this is that the full–scale span

of the MPX2010 (10 kPa sensor) will be only 40 mV due to the

device’s slightly lower sensitivity. Since the maximum supply

voltage produces the most output voltage, it is evident that

even the best case scenario will require some signal

conditioning to obtain a usable voltage level. For this specific

design, an MPX2100 and 5.0 V supply is used to provide a

maximum sensor output of 20 mV. The sensor output is then

signal conditioned to obtain a four volt signal swing (span).

Table 1. MPX2100 Electrical Characteristics for VS = 10 V, TA = 25°C

Characteristic

Symbol

Minimum

Typical

Max

Unit

Pressure Range

POP

100

kPa

Supply Voltage

Vdc

Full Scale Span

VFSS

38.5

41.5

Zero Pressure Offset

Voff

0.05

0.1

Sensitivity

0.4

mV/kPa

Linearity

0.05

%FSS

Temperature Effect on Span

0.5

%FSS

Temperature Effect on Offset

0.2

%FSS

MOTOROLA

SEMICONDUCTOR APPLICATION NOTE

REV 2

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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