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Analog and Interface Product Solutions

Temperature Sensor Design Guide
Temperature Measurement Solutions for Silicon IC Temperature Sensor, Thermocouple, RTD and Thermistor-Based Applications

Design ideas in this guide use the following devices. A complete device list and corresponding data sheets for these products can be found at www.microchip.com.
Voltage Output Temperature SensorsMCP9700 MCP9701 MCP9700A MCP9701A TC1046 TC1047A Logic Output Temperature Sensors TC620 TC621 TC622 TC623 TC624 TC6501 TC6502 TC6503 TC6504 Serial Output Temperature Sensors MCP9800 MCP9801 MCP9802 MCP9803 MCP9805 MCP98242 TC72 TC74 TC77 TCN75 TCN75A Comparators and Operational Amplifiers TC913A TC7650 TC7652 MCP616 MCP6541 MCP6542 MCP6543 MCP6544 MCP6001 MCP6021 MCP6231 MCP6271 MCP6281 MCP6291 PGAMCP6S21 MCP6S22 MCP6S24 MCP6S28

www.microchip.com/analog

Temperature Sensor Design Guide

TEMPERATURE SENSORS – OVERVIEW
In many systems, temperature control is fundamental. There are a number of passive and active temperature sensors that can be used to measure system temperature, including: thermocouple, resistive temperature detector, thermistor and silicon temperature sensors. Thesesensors provide temperature feedback to the system controller to make decisions such as, over-temperature shutdown, turn-on/off cooling fan, temperature compensation or general purpose temperature monitor. Microchip offers a broad portfolio of thermal management products, including Logic Output, Voltage Output and Serial Output Temperature Sensors. These products allow the system designer toimplement the device that best meets their application requirements. Key features include high accuracy, low power, extended temperature range and small packages. In addition, Microchip’s linear products can be used to support Thermocouple, RTD and Thermistor applications.

Silicon Output Temperature Sensors
Logic Output Temperature Sensors: Logic output temperature sensor families offer excellenttemperature accuracy (±1°C, typical), with a very low operating current of less than 600 μA. These devices can replace mechanical switches in a variety of sensing and control applications. Voltage Output Temperature Sensors: Voltage output temperature sensors develop an output voltage proportional to temperature, with a typical temperature coefficient of 6.25 mV/°C, 10 mV/°C and 19.5 mV/°Crespectively. These temperature-to-voltage converters can sense a -40°C to +125°C temperature range and feature an offset voltage that allows reading negative temperatures without requiring a negative supply voltage. The extremely low operating current minimizes self-heating and maximizes battery life. Serial Output Temperature Sensors: Serial (digital) output temperature sensors offer excellenttemperature accuracy (±0.5°C, typical) with a very low operating current of 250 μA (typical). Communication with these devices is accomplished via an industry standard SMBus, I2C™ or SPI compatible interface protocol. These devices feature fast temperature conversion rate, with temperature resolution for the entire family ranging from 0.0625°C to 0.5°C.

Common Methods of Interfacing a Sensor

SensorAnalog Output
Volts

Serial Output Logic Output
Fan
C

OFF ON

RTD

VDD

Op Amps/Comparators

VDD
R

MCP6541
R R

VREF

Thermistor/ Amplifiers Programmable Gain Amplifier (PGA)

R
+

VDD

MCP6S21
VOUT
Gain-Adjustment Input Selection

R

RT

-

C

SPI

Temperature Measurement Applications
Computing: – CPU overtemperature protection – Fan controlCellular/PCS: – Power amplifier temperature compensation – Thermal sensing of display for contrast control Power Supply Embedded Systems: – Overtemperature shutdown – Battery management

2

+

Thermocouple, Thermistor/Amplifiers

-

Thermocouples
VOUT

Thermocouples are usually selected because of their wide temperature range (as low as -270°C to as high as 1750°C), ruggedness and price;...