MCP3421EV Microchip Technology, MCP3421EV Datasheet - Page 31

• Manufacturer Part Number: MCP3421EV
• Description: BOARD EVAL FOR MCP3421 SOT23-6
• Manufacturer: Microchip Technology

Specifications of MCP3421EV

• Design Resources: MCP3421EV Gerber Files
• Number Of Adc's: 1
• Number Of Bits: 18
• Sampling Rate (per Second): 4
• Data Interface: Serial
• Inputs Per Adc: 1 Single Ended
• Input Range: ±2.5 V
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 125°C
• Utilized Ic / Part: MCP3421
• Silicon Manufacturer: Microchip
• Application Sub Type: ADC
• Kit Application Type: Data Converter
• Silicon Core Number: MCP3421
• Kit Contents: Board
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Not applicable / Not applicable

6.2.5
Figure 6-10
measurement using a thermocouple sensor and the
MCP9800 silicon temperature sensor. The MCP9800 is
a high accuracy temperature sensor that can detect the
temperature in the range of -55°C to 125°C with 1°C
accuracy.
The type K thermocouple sensor senses the
temperature at the hot junction (T
cold junction temperature (reference, T
temperature difference between the hot and cold
junctions is represented by the voltage V1. This voltage
is then converted to digital codes by the MCP3421.
In the circuit, the MCP9800 is used for cold junction
compensation. The MCU computes the difference of
the hot and cold junction temperatures, which is
proportional to the hot junction temperature (T
With
temperature from 0°C to 1250°C degrees. The full
scale output range of the Type K thermocouple is
about
(= 50 mV/1250°C)
Equation 6-2
mocouple sensor signal using the MCP3421 device
with 18 bits and PGA = 8 settings. With this configura-
tion, it 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 6-2:
© 2009 Microchip Technology Inc.
Where:
Detectable Input Signal Level
No. of LSB/°C
Input Signal Level after gain of 8:
1 LSB
Type
50 mV.
TEMPERATURE MEASUREMENT
=
shows the measurement budget for ther-
shows an example of temperature
K
=
15.625 µV with 18-bit configuration
thermocouple,
320
------------------------ -
15.625
of
μ
This
MEASUREMENT BUDGET
FOR THERMOCOUPLE
SENSOR
V/°C
=
μ
=
measurement
V
(
40
1.953125
=
=
μ
provides
V/°C
20.48 Codes/°C
15.625
HJ
) with respect to the
it
) 8
μ
•
μ
V for PGA
can
V/PGA
=
resolution.
320
CJ
40 µV/°C
measure
HJ
). The
μ
).
V/°C
=
8
FIGURE 6-10:
Measurement.
Equation 6-3
expected number of output code with various PGA gain
settings for Type K thermocouple output.
EQUATION 6-3:
Hot Junction
Where:
Thermocouple Sensor
Expected
Number of Output Code =
1 LSB = 15.625 µV with 18-bit configuration.
(T
HJ
~ 40 µV°C
)
Heat
Isothermal Block
shows an example of calculating the
MCP9800
Cold Junction (T
Example of Temperature
EXPECTED NUMBER OF
OUTPUT CODE FOR
TYPE K THERMOCOUPLE
V
V1
=
=
=
=
DD
log
11.6 bits for PGA
12.6 bits for PGA
13.6 bits for PGA
14.6 bits for PGA
MCP3421
2
⎛
⎜
⎜
⎝
----------------------- -
15.625
----------------------- -
50 mV
PGA
DS22003E-page 31
MCP3421
10 kΩ
CJ
V
10 kΩ
)
μ
DD
(MASTER)
SDA
To MCU
V
⎞
⎟
⎟
⎠
=
=
=
=
SCL
1
2
4
8