MCP6006RT datasheet(18/46 Pages) MICROCHIP

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MCP6006/6R/6U/7/9

DS20006411B-page 18

 2020-2021 Microchip Technology Inc.

4.8

Electromagnetic Interference

Rejection Ratio (EMIRR)

Definitions

The Electromagnetic Interference (EMI) is the

disturbance that affects an electrical circuit due to

either electromagnetic induction or electromagnetic

radiation emitted from an external source.

The parameter which describes the EMI robustness of

an op amp is the Electromagnetic Interference Rejec-

tion Ratio (EMIRR). It quantitatively describes the

effect that an RF interfering signal has on op amp

performance. Internal passive filters make EMIRR

better compared with older parts. This means that with

good PCB layout techniques, your EMC performance

should be better.

EMIRR is defined as:

EQUATION 4-1:

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

output of this voltage divider is fed into the noninverting

inputs of the MCP6006 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 MCP6006 op amp can be

used for conditioning this sensor.

In Figure 4-9, the variable resistor is used to calibrate

the sensor in different environments.

FIGURE 4-9:

CO Gas Sensor Circuit.

4.9.2

PRESSURE SENSOR AMPLIFIER

The MCP6006/6R/6U/7/9 is well-suited for conditioning

sensor signals in battery-powered applications. Many

sensors are configured as Wheatstone bridges. Strain

gauges and pressure sensors are two common

examples.

Figure 4-10 shows a strain gauge amplifier, using the

MCP6006/6R/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 outputs of pressure sensors, prevent resistive load-

ing 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 4-10:

Pressure Sensor Amplifier.

EMIRR dB



VRF

V

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





log



Where:

VRF = Peak Amplitude of

RF Interfering Signal (VPK)

VOS = Input Offset Voltage Shift (V)

VREF

VDD

VOUT

MCP6006

–

Strain Gauge

VOUT

Va Vb

–

 10k

100



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



VDD

VOUT

MCP6006

10 k



10 kΩ

100



100



VDD

R-∆R

R+∆R

VDD

½ MCP6007

R+∆R

R-∆R

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