Datasheet

MCP3425
DS22072B-page 28 © 2009 Microchip Technology Inc.
FIGURE 6-7: Example of Pressure
Measurement.
6.2.4 WHEATSTONE BRIDGE TYPE
SENSORS WITH SIGNAL
CONDITIONING
Wheatstone bridge is one of the most common
configurations in the sensor applications. Strain
gauges and pressure sensors are the common
examples. When the sensor output signal is small and
the common mode noise level is large, it needs a signal
conditioning circuit between the sensor and the
MCP3425. Figure 6-8 and Figure 6-9 show examples
of using the MCP6V01 (high precision auto-zeroed Op
Amp) for the sensor signal conditioning. Figure 6-8
shows the interface circuit with a minimum of
components between the sensor and the MCP3425,
but it is not symmetric, and therefore, the ADC input
becomes a single ended. On the other hand, the
Figure 6-9 has a symmetric and differential output, but
requires more components.
FIGURE 6-8: Simple Signal Conditioning
Design with Asymmetric Circuit.
FIGURE 6-9: High Performance Signal
Conditioning Design with Symmetric Circuit.
6.2.5 TEMPERATURE MEASUREMENT
Figure 6-10 shows an example of temperature
measurement using a thermistor. This example can
achieve a linear response over a 50°C temperature
range. This can be implemented using a standard
resistor with 1% tolerance in series with the thermistor.
The value of the resistor is selected to be equal to the
thermistor value at the mid-point of the desired
temperature range.
FIGURE 6-10: Example of Temperature
Measurement.
NPP301
MCP3425
V
IN
+
V
IN
-
V
DD
V
SS
1
2
3
4
5
6
SCL
SDL
10 µF0.1 µF
R
R
V
DD
V
DD
TO MCU
(MASTER)
V
DD
V
DD
RR
RR
100R
C
MCP6V01
V
DD
0.2R
0.2R
3kΩ
MCP3425
20 kΩ
1µF
20 kΩ
1µF
V
DD
1/2 MCP6V02
1/2 MCP6V02
200Ω
200Ω
3kΩ
3kΩ
1µF
RR
RR
V
DD
10 nF
10 nF
200Ω
MCP3425
200Ω
10 kΩ
Resistor
10 kΩ
Thermistor
MCP3425
V
IN
+
V
IN
-
V
DD
V
SS
1
2
3
4
5
6
SCL SDL
10 µF0.1 µF
R
pull-up
R
pull-up
V
DD
V
DD
TO MCU
(MASTER)
V
DD