Data Sheet

© 2009 Microchip Technology Inc. DS22088C-page 35
MCP3422/3/4
Equation 6-2 shows an example of calculating the
expected number of output code with various PGA gain
settings for Type K thermocouple output.
EQUATION 6-2: EXPECTED NUMBER OF
OUTPUT CODE FOR TYPE
K THERMOCOUPLE
FIGURE 6-7: Example of Pressure and Temperature Measurement.
Figure 6-7 shows an example of measuring both
pressure and temperature. The pressure is measured
by using NPP 301 (manufactured by GE NovaSensor),
and temperature is measured by a thermistor.
The pressure sensor output is 20 mV/V. This gives
100 mV of full scale output for V
DD
of 5V (sensor
excitation voltage). Equation 6-3 shows an example of
calculating the number of output code for the full scale
output of the NPP301.
log
2
50 mV
15.625 μ V
PGA
------------------------
------------------------
⎝⎠
⎜⎟
⎜⎟
⎛⎞
= 11.6 bits for PGA = 1
= 12.6 bits for PGA = 2
= 13.6 bits for PGA = 4
= 14.6 bits for PGA = 8
Expected
Number of Output Code =
Where:
1 LSB = 15.625 µV with 18 Bit configuration.
5kΩ
V
DD
4
5
6
9
CH2-
V
SS
CH3+
Adr1
Adr0
3
12
CH2+
CH3-
2
13
CH1-
CH4+
1
14
CH1+
CH4-
7
8
SDA
SCL
V
DD
11
10
0.1 µF
10 µF
TO MCU
(MASTER)
5kΩ
V
DD
Thermistor
V
DD
Pressure Sensor
V
DD
V
DD
V
DD
R
1
R
2
Thermistor
R
2
R
1
R
1
and R
2
= Voltage Divider
V
IN
R
2
R
1
R
2
+
-------------------
V
DD
× =
(NPP301)
Pressure Sensor
(NPP301)
V
IN
V
IN
MCP3424