MCP6V01-ESLASHMD datasheet(29/44 Pages) MICROCHIP

29 / 44 page

DS22058C-page 29

MCP6V01/2/3

4.4

Typical Applications

4.4.1

WHEATSTONE BRIDGE

Many sensors are configured as Wheatstone bridges.

Strain gauges and pressure sensors are two common

examples. These signals can be small and the

common mode noise large. Amplifier designs with high

differential gain are desirable.

Figure 4-15 shows how to interface to a Wheatstone

bridge with a minimum of components. Because the

circuit is not symmetric, the ADC input is single ended,

and there is a minimum of filtering, the CMRR is good

enough for moderate common mode noise.

FIGURE 4-15:

Simple Design.

Figure 4-16 shows a higher performance circuit for

Wheatstone bridges. This circuit is symmetric and has

high CMRR. Using a differential input to the ADC helps

with the CMRR.

FIGURE 4-16:

High Performance Design.

4.4.2

RTD SENSOR

The ratiometric circuit in Figure 4-17 conditions a three

wire RTD. It corrects for the sensor’s wiring resistance

by subtracting the voltage across the middle RW. The

top R1 does not change the output voltage; it balances

the op amp inputs. Failure (open) of the RTD is

detected by an out of range voltage.

FIGURE 4-17:

RTD Sensor.

The voltages at the input of the ADC can be calculated

with the following:

VDD

100R

0.01C

MCP6V01

ADC

VDD

0.2R

20 k

1µF

200

20 k

1µF

ADC

VDD

½ MCP6V02

200

1µF

VDD

10 nF

200

100 nF

10 nF

100 nF

ADC

VDD

½ MCP6V02

2.49 k

10 nF

VDD

RRTD

1µF

100

20 k

100 k

2.49 k

2.55 k

RTD VT

–

() G

WVW

RTD

–

()V

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

RTD

12 R

3 R2

⁄

⋅

RTD

3 R1

⁄

–

Where:

Voltage at the top of RRTD

Voltage at the bottom of RRTD

Voltage across top and middle

RW’s

VCM

ADC’s common mode input

VDM

ADC’s differential mode input

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