Data Sheet

MCP3422/3/4
DS22088C-page 34 © 2009 Microchip Technology Inc.
Figure 6-6, shows an example of using the
MCP3424 for four-channel thermocouple temperature
measurement applications.
FIGURE 6-6: Four-Channel Thermocouple Applications.
With Type K thermocouple, it can measure
temperature from 0°C to 1250°C degrees. The full
scale output range of the Type K thermocouple is
about 50 mV. This provides 40 µV/°C (= 50 mV/
1250°C) of measurement resolution. Equation 6-1
shows the measurement budget for sensor signal using
the MCP3422/3/4 device with 18 bits and
PGA = 8 settings. With this configuration, the
MCP3424 can detect the input signal level as low as
approximately 2 µV. The internal PGA boosts the input
signal level eight times. The 40 µV/°C input from the
thermocouple is amplified internally to 320 µV/°C
before the conversion takes place. This results in
20.48 LSB/°C output codes. This means there are
about 20 LSB output codes (or about 4.32 bits) per 1°C
of change in temperature.
EQUATION 6-1:
5kΩ
V
DD
4
5
6
9
CH2-
V
SS
CH3+
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)
MCP9800
MCP9800
MCP9800
MCP9800
Isothermal Block
Isothermal Block
Thermocouple Sensor
Heat
SCL
SDA
SDA
SCL
SDA
SCL
V
DD
SDA
SCL
SDA
SCL
Adr1
Adr0
5kΩ
MCP3424
Input Signal Level after gain of 8:
Where:
1 LSB = 15.625 µV with 18 bit configuration
Detectable Input Signal Level 15.625
μ V/PGA=
1.953125
μ V for PGA 8==
40
μ V/°C()8 320 μ V/°C= • =
No. of LSB/°C
320 μ V/°C
15.625
μ V
------------------------- 20.48 Codes/°C==