MCP6477-ESLASHMS datasheet(18/46 Pages) MICROCHIP

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MCP6476/6R/6U/7/9

DS20006419B-page 18

 2020-2021 Microchip Technology Inc.

4.9

Application Circuits

4.9.1

CARBON MONOXIDE GAS SENSOR

A Carbon Monoxide (CO) gas detector is a device that

detects the presence of carbon monoxide gas. Usually

this is battery powered and transmits audible and

visible warnings.

The sensor responds to CO gas by reducing its resis-

tance proportionaly to the amount of CO present in the

air exposed to the internal element. On the sensor

module, this variable is part of a voltage divider formed

by the internal element and potentiometer R1. The out-

put of this voltage divider is fed into the noninverting

inputs of the MCP6476 op amp. The device is config-

ured as a buffer with unity gain and is used to provide

a nonloaded test point for sensor sensitivity.

Because this sensor can be corrupted by parasitic

electromagnetic signals, the MCP6476 op amp can be

used for conditioning this sensor.

In Figure 4-8, the variable resistor is used to calibrate

the sensor in different environments.

FIGURE 4-8:

CO Gas Sensor Circuit.

4.9.2

PRESSURE SENSOR AMPLIFIER

The MCP6476/6R/6U/7/9 is well-suited for condition-

ing sensor signals in battery-powered applications.

Many sensors are configured as Wheatstone bridges.

Strain gauges and pressure sensors are two common

examples.

Figure 4-9 shows a strain gauge amplifier, using the

MCP6476/6R/6U/7/9 Enhanced EMI protection device.

The difference amplifier with EMI robustness op amp is

used to amplify the signal from the Wheatstone bridge.

The two op amps, configured as buffers and connected

at the outputs of pressure sensors, prevents resistive

loading of the bridge by resistors, R1 and R2. Resistors,

R1, R2 and R3, R5, need to be chosen with very low

tolerance to match the CMRR.

FIGURE 4-9:

Pressure Sensor Amplifier.

VDD

VOUT

MCP6476

VREF

VDD

Strain Gauge

VOUT

Va Vb

–

 10k

100



-------------



VDD

VOUT

MCP6476

10 k

100

VDD

R-

∆R

R+

∆R

VDD

½ MCP6477

R+

∆R

R-

∆R

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