Microchip Technology MCP6V01DM-VOS Data Sheet
© 2008 Microchip Technology Inc.
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.
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.
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.
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.
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.
high CMRR. Using a differential input to the ADC helps
with the CMRR.
FIGURE 4-16:
High Performance Design.
4.4.2
RTD SENSOR
conditions a three
wire RTD. It corrects for the sensor’s wiring resistance
by subtracting the voltage across the middle R
by subtracting the voltage across the middle R
W
. 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.
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:
with the following:
V
DD
R R
R R
100R
0.01C
MCP6V01
ADC
V
DD
0.2R
0.2R
3 k
Ω
20 k
Ω
1 µF
200
Ω
20 k
Ω
1 µF
ADC
V
DD
½ MCP6V02
½ MCP6V02
200
Ω
200
Ω
3 k
Ω
3 k
Ω
1 µF
R R
R R
V
DD
10 nF
10 nF
200
Ω
R
3
100 nF
10 nF
R
2
R
3
100 nF
ADC
V
DD
½ MCP6V02
½ MCP6V02
2.49 k
Ω
2.49 k
Ω
10 nF
V
DD
R
W
R
W
R
W
R
T
R
B
R
RTD
R
1
R
1
1 µF
100
Ω
3 k
Ω
3 k
Ω
20 k
Ω
20 k
Ω
100 k
Ω
100 k
Ω
2.49 k
Ω
2.49 k
Ω
R
2
2.55 k
Ω
2.55 k
Ω
V
DM
G
RTD
V
T
V
B
–
(
) G
W
V
W
+
=
V
CM
V
T
V
B
G
RTD
1
G
W
–
+
(
)V
W
+
+
2
------------------------------------------------------------------------------
=
G
RTD
1
2 R
3
R
2
⁄
⋅
+
=
G
W
G
RTD
R
3
R
1
⁄
–
=
Where:
V
T
=
Voltage at the top of R
RTD
V
B
=
Voltage at the bottom of R
RTD
V
W
=
Voltage across top and middle
R
R
W
’s
V
CM
=
ADC’s common mode input
V
DM
=
ADC’s differential mode input