AN897 Datasheet, PDF (10/16 Pages) Microchip Technology – Thermistor Temperature Sensing with MCP6SX2 PGAs

AN897
SUMMARY
Two different circuit designs using the MCP6SX2 PGA
and an accurate NTC thermistor have been shown.
The two designs trade off simplicity, accuracy and
temperature range.
The first design is easier to implement, but has a
smaller temperature range. It can be made more
accurate, or cover a wider temperature range, with
more expensive components and analog design effort.
While the second design’s firmware takes more space
in firmware, the analog design is very reasonable. It
takes advantage of the PGA’s flexibility and digital
control to reduce the analog errors and increase the
temperature resolution.
The MCP6SX2 PGA’s input MUX and digitally-
controlled gain significantly increase the utility of these
circuits. Multiple sensors and/or input signals can be
processed with one PGA, reducing component count.
It also makes it easier to perform temperature correc-
tion on other sensors. The marginal cost of the NTC
thermistor circuits is reasonable in this case.
REFERENCES
[1] “2322 640 5... : NTC thermistors, accuracy line,”
Product Data Sheet, BC Components^®,
September 27, 2001
(www.bccomponents.com).
[2] “Introduction to NTCs: NTC Thermistors,” Data
Sheet, BC Components, March 27, 2001
(www.bccomponents.com).
[3] AN685, “Thermistors in Single-Supply
Temperature Sensing Circuits,” Bonnie C.
Baker; Microchip Technology Inc., DS00685,
1999.
[4] AN867, “Temperature Sensing with a
Programmable Gain Amplifier,” Bonnie C.
Baker; Microchip Technology Inc., DS00867,
2003.
[5] MCP6S21/2/6/8 Data Sheet, “Single-Ended,
Rail-to-Rail I/O, Low-Gain PGA,” Microchip
Technology Inc., DS21117, 2003.
[6] MCP6S91/2/3 Data Sheet, “Single-Ended,
Rail-to-Rail I/O, Low-Gain PGA,”
Microchip Technology Inc., DS21908, 2004.
[7] AN248, “Interfacing MCP6S2X PGAs to
PICmicro^® Microcontroller,” Ezana Haile;
Microchip Technology Inc., DS00248, 2003.
[8] PIC16F684 Data Sheet, “14-Pin Flash-Based,
8-Bit MOS Microcontrollers with nanoWatt
Technology,” Microchip Technology Inc.,
DS41202, 2004.
[9] AN942, “Piecewise Linear Interpolation on
PIC12/14/16 Series Microcontrollers,” John Day
and Steven Bible; Microchip Technology Inc.,
2004.
[10] “PICkit™ 1 Flash Starter Kit User’s Guide,”
Microchip Technology Inc., DS40051, 2004.
[11] “Signal Analysis PICtail™ Daughter Board
User’s Guide,” Microchip Technology Inc.,
DS51476, 2004.
[12] “Thermistor PGA PICtail™ Daughter Board
User’s Guide,” Microchip Technology Inc.,
DS51517, 2004.
DS00897B-page 10
 2004 Microchip Technology Inc.