MCP3422 Datasheet, PDF (35/58 Pages) Microchip Technology – 18-Bit, Multi-Channel ΔΣ Analog-to-Digital Converter with I2C™ Interface and On-Board Reference

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
Expected
⎛
⎞
Number
of
Output
Code
=
l
og_{2⎜⎜}
⎝
-1-------55-----P-.0--6------G2----m--5--A----_μ--V------V-----_{⎠⎟⎟}
= 11.6 bits for PGA = 1
= 12.6 bits for PGA = 2
= 13.6 bits for PGA = 4
Where:
= 14.6 bits for PGA = 8
1 LSB = 15.625 µV with 18 Bit configuration.
V_DD
Pressure Sensor
(NPP301)
MCP3422/3/4
V_DD
Pressure Sensor
(NPP301)
V_DD
R₁
Thermistor
R₂
V_IN
0.1 µF
MCP3424
1 CH1+
2 CH1-
3 CH2+
4 CH2-
5 V_SS
6 V_DD
7 SDA
CH4- 14
CH4+ 13
CH3- ¹²
CH3+ ¹¹
Adr1 ¹⁰
Adr0 ⁹
SCL ⁸
10 µF
V_IN
V_DD
V_DD
R₁
R₂
TO MCU
(MASTER)
Thermistor
5 kΩ
5 kΩ
V_DD
V_IN
=
-------R----²-------
R₁ + R₂
×
V_DD
R₁ and R₂ = Voltage Divider
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.
© 2009 Microchip Technology Inc.
DS22088C-page 35