Microchip Technology MCP3421EV Data Sheet
MCP3421
DS22003E-page 30
© 2009 Microchip Technology Inc.
6.2.3
PRESSURE MEASUREMENT
shows an example of measuring the
pressure using NPP301 (manufactured by
GE NovaSensor). No external signal conditioning
circuit is needed by utilizing its internal PGA. The
pressure sensor output is 20 mV/V. This gives 100 mV
of full scale output for V
GE NovaSensor). No external signal conditioning
circuit is needed by utilizing its internal PGA. The
pressure sensor output is 20 mV/V. This gives 100 mV
of full scale output for V
DD
of 5V (sensor excitation
voltage).
shows an example of calculat-
ing the number of output code for the full scale output
of the NPP301.
of the NPP301.
FIGURE 6-7:
Example of Pressure
Measurement.
EQUATION 6-1:
EXPECTED NUMBER OF
OUTPUT CODE FOR
NPP301 PRESSURE
SENSOR
OUTPUT CODE FOR
NPP301 PRESSURE
SENSOR
6.2.4
WHEATSTONE BRIDGE TYPE
SENSORS WITH SIGNAL
CONDITIONING
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
MCP3421.
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
MCP3421.
show examples
of using the MCP6V01 (high precision auto-zeroed
Op Amp) for the sensor signal conditioning.
Op Amp) for the sensor signal conditioning.
shows the interface circuit with a minimum of compo-
nents between the sensor and the MCP3421, but it is
not symmetric, and therefore, the ADC input becomes
a single ended. On the other hand, the
nents between the sensor and the MCP3421, but it is
not symmetric, and therefore, the ADC input becomes
a single ended. On the other hand, the
a symmetric and differential output, but requires more
components.
components.
FIGURE 6-8:
Simple Signal Conditioning
Design with Asymmetric Circuit.
FIGURE 6-9:
High Performance Signal
Conditioning Design with Symmetric Circuit.
NPP301
MCP3421
V
IN
+
V
IN
-
V
DD
V
SS
1
2
3
4
5
6
SCL
SDL
10 µF
0.1 µF
R
R
V
DD
V
DD
T
O
MCU
(MASTER)
V
DD
Expected
log
2
100 mV
15.625
μ
V
PGA
------------------------
------------------------
⎝
⎠
⎜
⎟
⎜
⎟
⎛
⎞
Number of Output Code =
Where:
1 LSB
=
15.625 µV with 18 Bit configuration.
=
12.64 bits for PGA
=1
=
13.64 bits for PGA
=2
=
14.64 bits for PGA
=4
=
15.64 bits for PGA
=8
V
DD
R
R
R
R
100R
C
MCP6V01
V
DD
0.2R
0.2R
3 k
Ω
MCP3421
20 k
Ω
1 µF
20 k
Ω
1 µF
V
DD
1/2 MCP6V02
1/2 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
200
Ω
MCP3421