Data Sheet

MCP3426/7/8
DS22226A-page 32 © 2009 Microchip Technology Inc.
Figure 6-6, shows an example of using the MCP3428
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 MCP3426/7/8 device with 16 bits and PGA = 8
settings. With this configuration, the MCP3428 can
detect the input signal level as low as approximately
7.8 µV. By setting the internal PGA option to x8, the
40 µV/°C input from the thermocouple is amplified
internally to 320 µV/°C before the conversion takes
place. This results in about 5 LSB output codes per
1°C of change in temperature, with 16-bit conversion
mode.
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
MCP3428
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
Input Signal Level after gain of 8:
Where:
1 LSB = 62.5 µV with 16 bit configuration
Detectable Input Signal Level 62.5
μ V/PGA=
7.8125μV for PGA 8==
40
μ V/°C()8 320 μ V/°C= • =
No. of LSB/°C
320 μ V/°C
62.5
μ V
------------------------- 5.12 Codes/°C==