Temperature Sensor Design Guide

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 Sensors
Logic Output
Temperature Sensors
MCP9700
MCP9701
MCP9700A
MCP9701A
TC1046
TC1047A
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
PGA
MCP6S21
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. These sensors 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 to implement 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.
Common Methods of Interfacing a Sensor
Sensor
Volts
Serial Output
OFF ON
RTD
Fan
C
-
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; however, they are highly non-linear and
often require significant linearization algorithms. In addition,
the voltage output of this temperature sensing element is
relatively low when compared to devices that can convert
voltage signals to a digital representation. Consequently,
analog gain stages are required in the circuit.
MCP6541
VDD
R
R
R
VREF
Thermistor/
Amplifiers
Programmable
Gain Amplifier
(PGA)
VDD
R
+
R
RT
MCP6S21
VOUT
-
C
Gain-Adjustment
Input Selection
SPI
Temperature Measurement Applications
Computing:
– CPU overtemperature protection
– Fan control
Cellular/PCS:
– Power amplifier temperature compensation
– Thermal sensing of display for contrast control
Power Supply Embedded Systems:
– Overtemperature shutdown
– Battery management
2
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/°C
respectively. 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.
VDD
+
Op Amps/Comparators
Logic Output Temperature Sensors:
Logic output temperature sensor families offer excellent
temperature 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.
Serial Output Temperature Sensors:
Serial (digital) output temperature sensors offer excellent
temperature 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.
Analog Output
Logic Output
Silicon Output Temperature Sensors
Resistive Temperature Detectors (RTDs)
RTDs are able to sense temperatures with extreme accuracy,
have consistent and repeatable performance and low drift
error (-200°C to +850°C). For precision, these sensors also
require a linearization look-up table in the microcontroller due
to sensor non-linearities.
Thermistors
Thermistors (-100°C to +150°C) are normally used for
overtemperature shutdown purposes. Although not as
accurate as some of the other temperature sensor solutions,
thermistors are inexpensive and come in small packages. They
are also non-linear and require a temperature compensation
look-up table.
Temperature Sensor Design Guide
LOGIC OUTPUT TEMPERATURE SENSORS
Logic output sensors typically function as a thermostat,
notifying the system that a minimum or maximum temperature
limit has been reached. Sometimes referred to as a
temperature switch, these devices can be used to turn-on
either a fan or warning light when high or low temperature
conditions are detected. Since the output is typically not
latched, the switch will turn off when the temperature falls
below or rises above the temperature set point. Note that it is
necessary to have hysteresis so the switch does not “chatter”
when crossing the temperature set point.
TC6501/2/3/4 Key Features:
Most logic output temperature sensors are available in either
a Hot (for temperature-increasing applications) or Cold (for
temperature-decreasing applications) option. The hot and
cold options ensure that the hysteresis is in the appropriate
position, either below or above the temperature set point.
TC623 Key Features:
Factory-programmed Temperature Set Points
No External Components Required
Small SOT-23 Packages
TC620/1 Key Features:
Dual Trip Point Temperature Sensor
Wide Voltage Supply Range: +4.5V to +18V
User-programmable Trip Point and Hysteresis
Dual Trip Point Temperature Sensor
User-programmable Trip Point and Hysteresis
TC622/4 Key Features:
Low-Cost Single Trip Point Temperature Sensor
Temperature Set Point Easily Programs with a Single
External Resistor
TO-220 Package for Direct Mounting to Heatsink
Logic Output Temperature Sensor Key Features:
Logic-Level Output
Notifies System When Temperature is Above (or Below)
a Preset Value
Factory and User-programmable Temperature Settings
Available in a Variety of Output Configurations
Logic Output Temperature Sensor Applications:
Fan Controllers
Power Supplies
Motor Drives
RF Power Amplifiers
Logic Output Temperature Sensors Used as Temperature Switches
VDD
+12V
Overtemperature
Indicator
VDD
VDD
NTC
Thermistor
RLOW
THERM
VDD
12V DC
Brushless
Fan
RHIGH
HIGH SET
GND
GND
LOW LIMIT
CONTROL
TC621
VCC
TOVER
TC6501
LOW SET HIGH LIMIT
HYST
RSET
PIC®
MCU
OUT
Overtemperature
LED
TSET
TC622
Logic-Level
MOSFET
VDD
OUT
GND
INT
System
Controller
TC6501 Hot and Cold Options
Voltage
Temperature
Voltage
Temperature
3
Temperature Sensor Design Guide
VOLTAGE OUTPUT TEMPERATURE SENSORS
A Voltage Output Temperature Sensor provides an analog
output signal of varying voltage on a single pin. The output
voltage has a factory set slope (e.g., 10 mV/°C) and correlates
to the ambient temperature of the device. The device output
is typically connected to a stand-alone or integrated ADC
(Analog-to-Digital Converter).
TC1046 Key Features:
Wide Temperature Measurement Range: -40°C to +125°C
High Temperature Accuracy: ±0.5°C (typ.)
Linear Temperature Slope: 6.25 mV/°C
TC1047A Key Features:
Wide Temperature Measurement Range: -40°C to +125°C
High Temperature Accuracy: ±0.5°C (typ.)
Linear Temperature Slope: 10 mV/°C
The circuit shown below can be used to measure the LCD
panel’s temperature at multiple locations. The operational
amplifier functions as an averaging circuit to provide a
composite voltage output that can be used to adjust the LCD
contrast.
MCP6021 (Op Amp) Key Features:
Single-Supply: 2.5V to 5.5V
Rail-to-Rail Input and Output
Unity-Gain Stable
VDD/2 Reference Output
Voltage Output Temperature Sensor Key Features:
Easy System Integration
Reduces PCB Space
Low Current Consumption
Minimizes Design Time
MCP9700 Key Features:
Low Cost
Temperature Accuracy: ±1°C (typ.)
Voltage Output Temperature Sensor Typical Applications:
Cellular Phones
Temperature Measurement/Instrumentation
Consumer Electronics
MCP9700A Key Features:
Low Cost
Temperature Accuracy: ±1°C (typ.)
LCD Contrast Control
LCD Module
VDD
Upper-Left
Sensor
R
TC1047A
R
VDD
R
Lower-Right
Sensor
TC1047A
VDD
LCD
Adj. Module
+
MCP6021
Internal VDD
2
Reference Voltage
Using the TC1046 to Create a Simple Temperature Measurement System
7
8
RS
6
9
R/W
5
4
3
10
E
VDD
2
1
16
17
U1
20
11
RB4
12
RB5
13
RB6
14
RB7
2 x 20 LCD
Dot Matrix
15
VDD
1
18
RS
R/W
2
TC1046
VDD
Optional for
noisy applications
U2
E
RA5
2
24
3
4
25
5
6
27
7
R1
4.7 k
26
28
PIC16F872A
13
14
XTAL
32 kHz
16
10
17
18
8
19
4
RB6
RB7
11
15
C3
22 pF
RB4
RB5
12
9
3
22
23
RA5
C8
0.1 μF
21
C7
0.1 μF 1
C1
15 pF
C2
15 pF
Temperature Sensor Design Guide
VOLTAGE OUTPUT TEMPERATURE SENSORS
Linear Active Thermistors
The MCP9700/01 and MCP9700A/01A families of Linear
Active Thermistor® Integrated Circuits (ICs) are analog
temperature sensors that convert temperature to an analog
voltage output.
These sensors compete with a thermistor solution in price and
performance. Unlike resistive sensors (such as thermistors),
Linear Active Thermistor ICs do not require an additional signalconditioning circuit. Therefore, the biasing circuit development
overhead for thermistor solutions can be eliminated by
implementing these low-cost devices. The voltage output
pin (VOUT) can be directly connected to the ADC input of a
microcontroller.
The sensor output voltage is proportional to ambient
temperature with temperature coefficient of 10 mV/°C and
19.5 mV/°C with output voltage at 0°C scaled to 500 mV and
400 mV, respectively. These coefficients are ideal for 8-bit
Analog-to-Digital Converters referenced at 5V and 2.5V. The
operating current is 6 μA (typ.) and they use a PCB space
saving 5-pin SC-70/SOT-23 and 3-pin TO-92 packages.
MCP9700/01 Key Features:
5-pin SC-70 Package
3-pin TO-92 Package
5-pin SOT-23 Package
Operating temperature range: -40°C to 125°C
Temperature Coefficient: 10 mV/°C (MCP9700)
Temperature Coefficient: 19.5 mV/°C (MCP9701)
Low power: 6 μA (typ.)
MCP9700/01 and MCP9700A/01A
Typical Applications:
Entertainment Systems
Home Appliance
Battery Packs and Power Supplies for Portable Equipment
General Purpose Temperature Monitoring
Sensor Application Tips
The MCP9700/01 and MCP9700A/01A ICs are designed to
drive large capacitive loads. This capability makes the sensors
immune to board parasitic capacitance, which allows the
sensors to be remotely located and to drive long PCB trace
or shielded cables to the ADC. In addition, adding capacitive
load at VOUT helps the sensors transient response by reducing
overshoots or undershoots. This provides a more stable
temperature reading.
IC temperature sensors use analog circuitry to measure
temperature. Unlike digital circuits, analog circuits are more
susceptible to power-supply noise. It is recommended that a
bypass capacitor CBYPASS of 0.1 μf to 1 μf be placed at close
proximity to the VDD and VSS pins of the sensor. The capacitor
provides protection against power-supply glitches by slowing
fast transient noise. However, the effectiveness of the bypass
capacitor depends upon the power-supply source resistance.
Larger source resistance provides RC network with the CBYPASS
and adds a corner frequency to filter out the power-supply
noise. Adding a series resistor to the power-supply line is
adequate to increase the source resistance.
Typical Application Circuit For a Thermistor Solution
+5V
R*
VOUT
VDD
MCP9700/A
MCP9701/A
VSS
CLOAD*
CBYPASS
*Optional
5
Temperature Sensor Design Guide
VOLTAGE OUTPUT TEMPERATURE SENSORS
Typically, the accuracy of an IC temperature sensors is within
±1°C at room temperature and the accuracy error increases
exponentially at hot and cold temperature extremes. The
sensor error characteristic has a parabolic shape, which can
be described using a second order equation. The equation
can be used to compensate the sensor error to provide higher
accuracy over the operating temperature range. This is done by
evaluating the equation at the temperature of interest (sensor
output in degree Celsius) and subtracting the result from the
sensor output. The subtracted result in °C is the compensated
sensor output.
Graph 1: MCP9800 2nd Order Equation
2.0
Typical Results
Equation 1, 2 and 3 show the 2nd order error equation of the
tested parts for the MCP9800, MCP9700/A and MCP9701/A,
respectively. Since these devices have functional differences,
the operating temperature range and temperature error
coefficients differ. The equations below describe the typical
device temperature error characteristics.
0.0
-1.0
Sensor Accuracy
-3.0
-55 -35 -15
5
25 45 65
Temperature (°C)
85
105 125
Graph 2: MCP9700/A 2nd Order Equation
MCP9700/A
3.0
2.0
Accuracy (°C)
A short look-up table can also be generated for low-level PIC
microcontrollers such as PIC10FXX, PIC12FXXX, PIC14FXXX
and PIC16FXXX. For additional information, see AN1001:
IC Temperature Sensor Accuracy Compensation with a PIC®
Microcontroller.
Compensated Sensor Accuracy
1.0
-2.0
For higher accuracy, the equation can be computed using
a standard PIC microcontroller, such as PIC16FXXXX,
PIC18FXXXX, PIC24FXXXX or dsPIC30FXXXX.
Compensated Sensor Output (°C) = Sensor Output (°C)
– Sensor Error|Sensor Output (°C)
MCP9800
3.0
Accuracy (°C)
IC Sensor Compensation Technique
Compensated Sensor Accuracy
1.0
0.0
-1.0
-2.0
Sensor Accuracy
-3.0
-55
-35
-15
5
25 45 65
Temperature (°C)
85
105 125
Equation 1: MCP9800 2nd Order Equation
Where:
= 150 x 10-6°C/°C2
EC2
EC1
= 7 x 10-3°C/°C
Error-55 = -1.5°C
Equation 2: MCP9700/A 2nd Order Equation
ErrorT_2 = EC2(125°C – TA) • (TA – -40°C)
+ EC1(TA – -40°C) + Error-40
Where:
EC2
= 244 x 10-6°C/°C2
EC1
= 2 x 10-12°C/°C » 0°C/°C
Error-40 = -2°C
Equation 3: MCP9701/A 2nd Order Equation
ErrorT_2 = EC2(125°C – TA) • (TA – -515°C)
+ EC1(TA – -15°C) + Error-15
Where:
EC2
= 200 x 10-6°C/°C2
EC1
= 1 x 10-3°C/°C
Error-15 = -1.5°C
6
Graph 3: MCP9701/A 2nd Order Equation
MCP9701/A
3.0
2.0
Accuracy (°C)
ErrorT_2 = EC2(125°C – TA) • (TA – -55°C)
+ EC1(TA – -55°C) + Error-55
Compensated Sensor Accuracy
1.0
0.0
-1.0
-2.0
Sensor Accuracy
-3.0
-15
5
25
45
65
85
Temperature (°C)
105
125
Temperature Sensor Design Guide
SERIAL OUTPUT TEMPERATURE SENSORS
MCP9800/1/2/3 Key Features:
Typically, serial output temperature sensors use a two or three
wire interface to the host controller and provide functions
that are user programmable. Functions such as temperature
alert output allow the user to configure the device as a standalone temperature monitoring system. The alert output can be
used to notify the system controller to act upon the change in
temperature. This feature eliminates the need for the system
controller to monitor temperature continuously using the serial
interface.
±1°C (max.) Accuracy From -10°C to +85°C
Supply Current: 200 μA (typ.)
One Shot Temperature Measurement
TC72 Key Features:
10-Bit Temperature-to-Digital Converter
Power-saving One-shot Temperature Measurement
Low Power Consumption
The figure below illustrates a multi-zone temperature
measurement application. Communication with the MCP9801
is accomplished via a two-wire I2C™/SMbus compatible serial
bus. This device can be set to notify the host controller when
the ambient temperature exceeds a user-specified set point.
The microcontroller can monitor the temperature of each
sensor on the serial bus by either reading the temperature
data register or functioning as a stand-alone thermostat. The
temperature threshold trip point is programmed by writing to
the set point register. The ALERT pin is an open-drain output
that can be connected to the microcontroller’s interrupt pin for
overtemperature interrupt.
TC74 Key Features:
Simple 2-wire Serial Interface
Digital Temperature-sensing in SOT-23-5 or TO-22-5
Packages
Low Power Consumption
TC77 Key Features:
13-Bit Temperature-to-Digital Converter
Low Power Consumption
±1°C (max.) Accuracy From +25°C to +65°C
SPI Compatible Communications Interface
Serial Output Temperature Sensor Applications:
TCN75 Key Features:
Personal Computers
Set-top Boxes
Cellular Phones
General Purpose Temperature Monitoring
Industry Standard SMBus/I2C™ Interface
Programmable Trip Point and Hysteresis
Thermal Event Alarm Output Functions as Interrupt or
Comparator/Thermostat Output
A Multi-zone Temperature Measurement System Using the Two-wire Serial Communication Port of the MCP9801
VDD
R
R
GP2/INT
SDA
SCL
®
R
SDA
SCL
PIC
MCU
MCP9801
System
Controller
SDA
SCL
INT
V+
ADC
VDD
ALERT
MCP9801
V+
A0
A0
A0
A1
A2
A1
A2
A1
A2
Sensor #0
MCP9801
SDA
SCL
INT
Clock
Generator
Counter/
Accumulator
Sensor #1
Control
Logic
Address
Decoder
Serial Bus
Interface
Data Registers
Calibration Registers
Temperature Data
Offset Correction
Temp. Set Point
Gain Correction
Temp. Hysteresis
Configuration Registers
Control
Set Point
Comparator
INT
MCP9801
Sensor #7
A0
A1
A2
DATA
CLK
VDD
Manufacturer/Ver. ID
7
Temperature Sensor Design Guide
DIGITAL TEMPERATURE SENSOR
Typical Application
The MCP9805 digital temperature sensor is designed to
meet the JEDEC standard JC42.4 for Mobile Platform Memory
Module Thermal Sensor. This device provides an accuracy of
±1°C (max.) from a temperature range of +75°C to +95°C
(active range) and ±2°C (max.) from +40°C to +125°C (monitor
range) as defined in the JEDEC standard. In addition, this
device has an integrated 256 byte EEPROM for SPD.
Memory Module
Memory
SPD*
Temperature
Sensor
EEPROM
MCP9805
MCP9805 Key Features:
Accuracy with 0.25°C/LSb Resolution:
– ±1°C (max.) from +75°C to +95°C
– ±2°C (max.) from +40°C to +125°C
– ±3°C (max.) from -20°C to +125°C
256 byte EEPROM for SPD
Operating Current: 200 μA (typ.)
Shutdown Current: 0.1 μA (typ.)
R
R
MCP9805 Applications:
3.3 VDD_SPD
Dual In-line Memory Module (DIMM)
Personal Computers (PCs) and Servers
Hard Disk Drives and Other PC Peripherals
General Purpose Temperature Sensor
SDA SCLK
* Serial Presence Detect
Register Structure Block Diagram
Event Output Hysteresis
Continuous Conversion or Shutdown
Critical Boundary Trip Lock
Event Boundary Window Lock Bit
Clear Event Output Interrupt
Event Output Status
Enable/Disable Event Output
Critical Event Output only
Event Output Polarity, Active-High/Low
Band Gap
Temperature
Sensor
Event Output Comparator/Interrupt
Configuration Register
DS ADC
Temperature Register (TA)
Temperature Upper-Boundary (TUPPER)
Temperature Lower-Boundary (TLOWER)
Critical Temperature Limit (TCRIT)
Manufacturer Identification Register
Device Identification and Revision Register
Device Capability Register
Measurement Resolution
Measurement Range
Measurement Accuracy
Temperature Event Output
SMBus/Standard I2C™
Interface
Register Pointer
A0
8
A1
A2
Event
VDD
GND
SDA
SCLK
Event
Temperature Sensor Design Guide
DIGITAL TEMPERATURE SENSOR
The MCP98242 digital temperature sensor is designed to
meet the JEDEC standard JC42.4 for Mobile Platform Memory
Module Thermal Sensor. This device provides an accuracy of
±1°C (max.) from a temperature range of +75°C to +95°C
(active range) and ±2°C (max.) from +40°C to +125°C (monitor
range) as defined in the JEDEC standard.
Typical Application
DIMM Module
Memory
MCP98242 Key Features:
Accuracy with 0.25°C/LSb Resolution:
– ±1°C (max.) from +75°C to +95°C
– ±2°C (max.) from +40°C to +125°C
– ±3°C (max.) from -20°C to +125°C
256 byte EEPROM for SPD
Shutdown Current: 0.1 μA (typ.)
MCP98242
Temperature Sensor
+ EEPROM
±0.5°C (typ.) Sensor
256 byte EEPROM for SPD
MCP98242 Applications:
Dual In-line Memory Module (DIMM)
Personal Computers (PCs) and Servers
Hard Disk Drives and Other PC Peripherals
General Purpose Temperature Sensor
3.3 VDD_SPD
SDA
SCL
Event
Register Structure Block Diagram
Temperature Sensor
EEPROM
Hysteresis
Shutdown
Critical Trip Lock
Alarm Win Lock Bit
HV Generator
Clear Event
Event Status
Output Control
Critical Event Only
WriteProtected
Array
(80h-7Fh)
Event Polarity
Event Comp/Int
Band Gap
Temperature
Sensor
Configuration
Temperature
Address
Decoder
X
ΔΣ ADC
TUPPER
Standard
Array
(80h-FFh)
TLOWER
0.5°C/bit
0.25°C/bit
0.125°C/bit
0.0625°C/bit
TCRIT
Manufacturer ID
Memory
Control
Logic
Device ID/Rev
Resolution
Write Protect
Circuitry
Capability
Selected Resolution
Address Decoder
Y
Temp. Range
Accuracy
Output Feature
Sense Amp
R/W Control
Register
Pointer
SMBus/Standard I2C™
Interface
A0
A1
A2
Event
SDA
SCL
VDD
GND
9
Temperature Sensor Design Guide
THERMOCOUPLES
Thermocouples
The thermocouple can quantify temperature as it relates to a
reference temperature. This reference temperature is usually
sensed using a Thermistor, RTD or Integrated Silicon Sensor.
The wide temperature ranges of the thermocouple make it
appropriate for many hostile sensing environments.
The thermocouple consists of two dissimilar metallic wires that
are connected at two different junctions, one for temperature
measurement and the other for reference. The temperature
difference between the two junctions is determined by
measuring the change in voltage across the dissimilar metals
at the temperature measurement junction.
The Instrument Society of America (ISA) defines a number
of commercially available thermocouple types in terms of
performance. Type E, J, K and T are base-metal thermocouples
and can be used to measure temperatures from about -200°C
to 1000°C. Type S, R and B are noble-metal thermocouples
and can be used to measure temperatures from about -50°C to
2000°C.
The TC913A auto-zeroed op amp is selected because of its
low offset voltage of 15 μV (max.) and high Common Mode
Rejection Ratio (CMRR) of 116 dB (typ.). Auto-zero and chopper
amplifiers are good thermocouple amplifiers due to their low
offset voltage and CMRR specifications.
The cold junction compensation circuit is implemented with the
TC1047A silicon IC temperature sensor located on the PCB.
Thermocouple Key Features:
Self-powered
-270°C to 1750°C
Remote Sensing
Robust Sensor
Thermocouple Applications:
Stoves
Engines
Thermopiles
Silicon Sensors for Cold Junction Compensation:
The circuit shown below can be used for remote thermocouple
sensing applications. The thermocouple is connected to the
circuitry via a shielded cable and EMI filters. The thermocouple
is tied to a positive and negative supply via large resistors so
that the circuit can detect a failed open-circuit thermocouple.
TC1047A Analog Temperature Sensor
MCP9800 12-bit Serial Output Temperature Sensor
Thermocouple Amplifier Circuit
+V
Thermocouple
R
<<
EMI Filter
<<
EMI Filter
+V
TC1047A
10
+V
R
–
+
R
<<
R
–V
R
R
C
IN_1
TC913A
C
ADC
-V
Cold Junction Compensation
IN_2
Temperature Sensor Design Guide
RESISTIVE TEMPERATURE DETECTORS (RTDs)
RTDs
RTD Key Features:
Extremely Accurate with Excellent Linearity
Variety of Packages
RTDs (Resistive Temperature Detectors) serve as the standard
for precision temperature measurements due to their excellent
repeatability and stability characteristics. RTDs provide the
designer with an absolute result that is fairly linear over
temperature. The RTD’s linear relationship between resistance
and temperature simplifies the implementation of signalconditioning circuitry.
Wire-wound or Thin-film
RTD Applications:
Industrial Instrumentation
Hot Wire Anemometers
Laboratory-quality Measurements
Circuit A below is easy to modify for a desired temperatureto-frequency range. It requires either precision, low-drift
components or a calibration step to achieve high accuracy.
Circuit B utilizes pull-up and pull-down resistors to excite
the RTD, employing the TC913A op amp to amplify the small
voltage changes that correspond to temperature.
Recommended Products:
TC913A/B – Auto-zero Op Amps
TC7650/2 – Chopper-stabilized Op Amps
MCP616/7/8/9 – Micropower Bi-CMOS Op Amps
MCP6021/2/4 – 10 MHz Bandwidth Op Amps
MCP6041/2/3/4 – 600 nA, Rail-to-Rail Input/Output Op Amps
MCP6541/2/3/4 – Push-Pull Output Sub-Microamp
Comparators
MCP6S21/2/6/7 – Single-ended, Rail-to-Rail Input/
Output Low-gain Programmable Gain Amplifiers (PGAs)
RTD Temperature Measurement Circuits
RTD
VDD
C
+
Circuit A
MCP6541
VOUT
-
R
VDD
R
R
Circuit B
VREF
Connector
R
R
R
EMI Filter
-
RTD
TC913A
+
EMI Filter
Shielded
Cable
R
R
R
PCB
11
Temperature Sensor Design Guide
THERMISTORS (THERMALLY SENSITIVE RESISTORS)
Thermistors are built with semiconductor materials and can
have either a positive (PTC) or negative (NTC) temperature
coefficient. However, the NTC is typically used for temperature
sensing.
Advantages of thermistors include a very high sensitivity to
changes in temperature (having a thermal response of up to
-100Ω/°C at 25°C), fast response time and low cost. The main
drawback of thermistors is that the change in resistance with
temperature is highly non-linear at temperatures below 0°C and
greater than 70°C.
A conventional fixed gain thermistor amplifier circuit is shown
below. A simple voltage divider is created with a reference
resistor (R1) and the thermistor (RT). A constant voltage source
is supplied (VREF) with the output of the voltage divider (VTH)
directly correlating to temperature. The response is shown in
the graph of temperature vs. output voltage to the right of the
circuit. It is fairly linear in the range of 0-70°C, but the accuracy
of the circuit is limited without adding additional circuitry.
The advantage of the PGA circuit (below) is illustrated by
comparing the VOUT slope plots of the conventional circuit
with the PGA circuit. The VOUT slope for the PGA circuit has a
minimum value of 30 mV for temperatures greater than 35°C,
which means that only a 9-bit ADC is required. In contrast, a
voltage divider with a gain of 1 will require an 11-bit, or higher,
ADC to provide an equivalent temperature resolution. The
resolution of a thermistor circuit is important in applications
such as overtemperature shutdown circuits.
Thermistor Key Features:
Inexpensive
Two-wire Measurement
Variety of Packages
Thermistor Applications:
Battery Chargers
Power Supplies
Cold Junction Compensation
Conventional Fixed Gain Thermistor Amplifier
VREF
R2
100K
VDD
VTH
+
MCP6001
VOUT
RT = 10K
@ 25°C
C1
1F
VOUT (V)
R1 4.53K
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
G = +1 V/V
-50
-25
0
25
50
75
100
125
150
Thermistor Temperature (°C)
VOUT
RT = 10K
@ 25°C
C1
1F
–
Gain Adjustment
Input Selection
Hysteresis
-50
SPI
12
G = +32
MCP6S21
+
G = +16
100K
G = +8
R2
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
G = +4
VDD
VOUT (V)
RS
28K
G = +1
VREF
G = +2
PGA Circuit Interfaced with a Thermistor
-25
0
25
50
75 100 125
Thermistor Temperature (°C)
150
Temperature Sensor Design Guide
RELATED SUPPORT MATERIAL
The following Application Notes are available on the Microchip
web site: www.microchip.com.
Application Notes
General Temperature Sensing
AN679: Temperature Sensing Technologies
The most popular temperature sensor technologies are
discussed at a level of detail that will give the reader insight
into the methods for determining which sensor is most
appropriate for a particular application.
AN867: Temperature-Sensing with a Programmable Gain
Amplifier
The implementation of temperature measurement systems
from sensor to PIC® microcontroller using a NTC thermistor,
silicon temperature sensor, anti-aliasing filter, A/D converter
and microcontroller are discussed.
AN929: Temperature Measurement Circuits for Embedded
Applications
Explores selection techniques for temperature sensor and
conditioning circuits to maximize the measurement accuracy,
while simplifying the interface to a microcontroller.
AN1001: IC Temperature Sensor Accuracy Compensation with a
PICmicro® Microcontroller
The typical accuracy of analog and serial-output IC temperature
sensors is within ±1°C, however, at hot or cold extremes,
the accuracy decreases non-linearly. This application note
is based on the analog output MCP9700/9701 and serial
output MCP9800 temperature sensors. It derives an equation
describing the sensor’s typical non-linear characteristics, which
can be used to compensate for the sensor’s accuracy error
over the specified operating temperature range.
Silicon IC Temperature Sensors
Analog Output
AN938: Interfacing a TC1047A Analog Output Temperature
Sensors to a PICmicro® Microcontroller
Discusses system integration, firmware implementation and
PCB layout techniques for using the TC1047A in an embedded
system.
TB051: Precision Temperature Measurement Technical Brief
Logic Output
AN762: Applications of the TC62X Solid-State Temperature
Sensor
Sensing temperature and comparing that temperature to preset
limits is the basis for a variety of problems that designers
face in system design and process control. This Application
Note discusses the new generation of small, easy-to-use,
temperature-sensing products provided by Microchip; namely,
the TC62X product family.
AN773: Application Circuits of the TC620/TC621 Solid-State
Temperature Sensors
Discusses the benefits of the TC620/TC621 solid-state
temperature sensors.
Serial Output
AN871: Solving Thermal Measurement Problems Using the
TC72 and TC77 Digital Silicon Temperature Sensors
Discusses the benefits of the TC72/TC77 temperature sensors
by analyzing their internal circuitry, illustrating the principles
these sensors employ to accurately measure temperature.
AN913: Interfacing the TC77 Thermal Sensor to a PICmicro®
Microcontroller
Discusses system integration, firmware implementation and
PCB layout techniques for using the TC77 in an embedded
system.
AN940: Interfacing the TC72 SPI Digital Temperature Sensor
to a PICmicro® Microcontroller
Techniques for integrating the TC72 into an embedded system
are demonstrated using the PICkit™ Flash Starter Kit.
TB050: Monitoring Multiple Temperature Nodes Using TC74
Thermal Sensors and a PIC16C505
The PIC16C505 is a 14-pin MCU that can easily interface to
the TC74. This Technical Brief illustrates the ease of interfacing
these two products.
TB052: Multi-Zone Temperature Monitoring with the TCN75
Thermal Sensor
Presents an example of a simple, multi-zone thermal-monitoring
system using the Hardware mode of the Master Synchronous
Serial Port (MSSP) module of a PIC® microcontroller.
Provides a description for interfacing a TC1046 temperature
sensor to a PIC16F872 microcontroller. A 2 x 20 dot matrix
LCD is included in the design to provide additional functionality.
13
Temperature Sensor Design Guide
RELATED SUPPORT MATERIAL
Thermocouples
Demonstration/Evaluation Kits
AN684: Single-Supply Temperature Sensing with
Thermocouples
For additional information on these and other analog
demonstration and evaluation kits, visit the Microchip web site
at: www.microchip.com/analogtools
This Application Note focuses on circuit solutions that use
thermocouples in their design. The signal-conditioning path for
the thermocouple system is discussed, followed by complete
application circuits.
RTDs
AN687: Precision Temperature Sensing with RTD Circuits
MCP9700 Temperature-to-Voltage Converter PICtail™
Demonstration Board
Part Number: MCP9700DM-PCTL
MCP9800 Temp Sensor PICtail™
Demonstration Board
Part Number: MCP9800DM-PCTL
Focuses on circuit solutions that use platinum RTDs in their
design.
AN895: Oscillator Circuits for RTD Temperature Sensors
Demonstrates how to design a temperature sensor oscillator
circuit using Microchip’s low-cost MCP6001 operational
amplifier and the MCP6541 comparator.
Thermistors
MCP9800 Temperature Data Logger Demonstration Board
Part Number: MCP9800DM-DL
TC72 Digital Temperature Sensor PICtail™
Demonstration Board
Part Number: TC72DM-PICTL
AN685: Thermistors in Single-Supply Temperature Sensing
Systems
Focuses on circuit solutions that use Negative Temperature
Coefficient (NTC) thermistors in their design.
AN897: Thermistor Temperature Sensing with MCP6S2X PGA
Presents two circuits that employ a precise, Negative
Temperature Coefficient (NTC) thermistor for temperature
measurement.
TC74 Serial Digital Thermal Sensor Demonstration Board
Part Number: TC74DEMO
TC77 Thermal Sensor PICtail™ Demonstration Board
Part Number: TC77DM-PICTL
TC64X/64XB Fan Speed Controller Demonstration Board
Part Number: TC642DEMO
TC64X/64XB Fan Speed Controller Evaluation Board
Part Number: TC642EV
TC650 Fan Controller Demonstration Board
Part Number: TC650DEMO
TC652 Fan Controller Demonstration Board
Part Number: TC652DEMO
TC1047A Temperature-to-Voltage Converter PICtail™
Demonstration Board
Part Number: TC1047ADM-PICTL
14
15
0.5/1
0.5/1
I2C™
I2C™
SMBus
SMBus
SMBus
MCP9800
MCP9801
MCP9802
MCP9803
MCP9805
MCP98242
0.5/2
0.5/2
SMBus/I2C
SMBus/I2C
4-Wire SPI
3-Wire SPI
TC74
TCN75
TC72
TC77
2.7
-40 to +125
Accuracy @ 25°C
(Typ./Max)
1/3
1/3
1/5
1/3
1/5
0.5/4
0.5/4
0.5/4
0.5/4
Device
TC620
TC621
TC622
TC623
TC624
TC6501
TC6502
TC6503
TC6504
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
Temperature Range (°C)
60
60
12
12
12
12
IQ Max.
(μA)
Temperature Set Points
4.4
4.4
5.5
5.5
5.5
5.5
VDD Max.
(V)
Factory programmed thresholds
Factory programmed thresholds
Factory programmed thresholds
Factory programmed thresholds
User-selectable, set by external resistor
User-selectable, set by external resistor
User-selectable, set by external resistor
User-selectable, set by external resistor
2.7
2.65
2.7
2.7
3.0
3.0
2.7
2.7
2.7
2.7
2.7
2.7
2.7
2.7
2.7
2.7
4.5
4.5
4.5
VDD Min.
(V)
10
6.25
19.5
19.5
10
10
400
400
1000
350
500
500
400
400
400
400
5.5
5.5
5.5
5.5
4.5
4.5
18
18
18
VDD Max
(V)
500
424
400
400
500
500
40
40
40
40
300
250
600
400
400
IQ Max.
(μA)
Packages
SOIC-8, SOT-23-5
MSOP-8, 2x3 DFN-8
SOIC-8, MSOP-8
SOT-23-5, TO-220-5
TSSOP-8, 2x3 DFN-8
TSSOP-8, 2x3 DFN-8
SOIC-8, MSOP-8
SOT-23-5
SOIC-8, MSOP-8
SOT-23-5
Packages
Packages
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
PDIP-8, SOIC-8
PDIP-8, SOIC-8
PDIP-8, SOIC-8, TO-220-5
PDIP-8, SOIC-8
PDIP-8, SOIC-8
SOT-23-3
SOT-23-3
SC-70-5
SC-70-5, TO-92-3
SC-70-5
SOT-23-5, SC-70-5, TO-92-3
IQ Max. (μA)
Offset Voltage
(Output @ 0°C) (mV)
5.5
5.5
5.5
5.5
3.6
3.6
5.5
5.5
5.5
5.5
VDD Max (V)
Slope
(mV/°C)
VDD Min. (V)
User-selectable, set by external resistor
2.7
3.1
3.1
2.3
2.3
VDD Min.
(V)
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
Temperature Range (°C)
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
Temperature Range
(°C)
Logic Output Temperature Sensor Products
0.5/2.0
1/2
MCP9701A
TC1047/A
1/4
MCP9701
0.5/2.0
1/2
MCP9700A
TC1046
1/4
Accuracy @ 25°C
(Typ./Max)
MCP9700
Device
Analog (Voltage Output) Temperature Sensor Products
0.5/1
0.5/1
2/3 (0.5/1 75°C-95°C)
SMBus
2/3 (0.5/1 75°C-95°C)
0.5/1
0.5/1
Accuracy @ 25°C
(Typ./Max)
Device
Serial Communication
Serial Output Temperature Sensor Products
See Microchip’s Advanced Parts Selector (MAPS) software for complete product selection and specifications.
–
–
–
–
–
–
–
–
–
Development Tools
TC1047ADM-PCTL
–
–
–
MCP9700DM-PCTL
MCP9700DM-PCTL
Development Tools
TC77DM-PCTL
TC72DM-PICTL
–
TC74DEMO
–
–
–
–
–
MCP9800DM-DL
MCP9800DM-PCTL
Development Tools
Temperature Sensor Design Guide
SELECTED PRODUCT SPECIFICATIONS
15
16
1, 2, 4
1, 2, 4
1, 2, 4
1, 2, 4
1, 2, 4
1, 2, 4
1, 2, 4
1, 2, 4
MCP616
MCP6001
MCP6041
MCP6141
MCP6231
MCP6271
MCP6281
MCP6291
2
1
4
MCP6542
MCP6543
MCP6544
4
4
4
4
1
2
6
8
MCP6S22
MCP6S26
MCP6S28
Channels
MCP6S21
Device
2 to 12
2 to 12
2 to 12
2 to 12
-3 db BW (MHz)
1.1
1.1
1.1
1.1
IQ Typical (mA)
1
1
1
1
IQ Typical
(μA)
±2
275
275
275
275
VOS (μV)
5
5
5
5
±1
2.4 to 5.5
7.2 to 5.5
2.0 to 5.5
1.8 to 5.5
1.4 to 5.5
1.4 to 5.5
1.8 to 5.5
2.3 to 5.5
2.7 to 5.5
5 to 16
4.5 to 16
6.5 to 16
Operating
Voltage Range (V)
2.5 to 5.5
2.5 to 5.5
2.5 to 5.5
2.5 to 5.5
Operating Voltage (V)
1.6 to 5.5
1.6 to 5.5
1.6 to 5.5
1.6 to 5.5
Operating Voltage (V)
50
Packages
100
-40 to +85
-40 to +85
-40 to +85
-40 to +85
Temperature Range (°C)
-40 to +85
-40 to +85
-40 to +85
-40 to +85
Packages
TO-92-3, SOT-23B-3
Packages
PDIP-16, SOIC-16
PDIP-14, SOIC-14, TSSOP-14
PDIP-8, SOIC-8, MSOP-8
PDIP-8, SOIC-8, MSOP-8
Packages
PDIP-14, SOIC-14, TSSOP-14
PDIP-8, SOIC-8, MSOP-8
PDIP-8, SOIC-8, MSOP-8
PDIP-8, SOIC-8, MSOP-8, SOT-23-5
Max. Supply Current
(μA @ 25°C)
TSSOP-14, PDIP-8, SOIC-8, MSOP-8, SOT-23-5
TSSOP-14, PDIP-8, SOIC-8, MSOP-8, SOT-23-5
TSSOP-14, PDIP-8, SOIC-8, MSOP-8, SOT-23-5
TSSOP-14, PDIP-8, SOIC-8, SOT-23-5, SC-70-5
TSSOP-14, PDIP-8, SOIC-8, MSOP-8, SOT-23-5
TSSOP-14, PDIP-8, SOIC-8, MSOP-8, SOT-23-5
SOT-23-5, SC-70-5
PDIP-8, SOIC-8, MSOP-8
TSSOP-14, PDIP-8, SOIC-8, SOT-23-5
PDIP-8, PDIP-14
PDIP-8, PDIP-14
PDIP-8
Temperature Range (°C)
Temperature Coefficient
(ppm/°C)
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +125
-40 to +85
-40 to +125
0 to +70
0 to +70
0 to +70
Temperature Range
(°C)
Initial Accuracy
(%)
VOS Max
(mV)
3
3
3
7
3
3
7
0.15
2
0.05
0.05
0.15
VOS Max.
(mV)
Max Load Current
(mA)
1000/1300
450/570
120/240
20/30
0.6/1
0.6/1
100/170
19/25
230/325
1000/3000
2000/3500
8500/1100
IQ (Typ./Max)
(μA)
Typical Propagation
Delay (μsec)
2.5
Output Voltage
(V)
10,000
5000
2000
300
100
14
1000
190
2800
400
2000
1500
GBWP (kHz)
Programmable Gain Amplifiers (PGAs)
1
MCP6541
Device
# per
Package
2.7 to 5.5
MCP1525
Comparators
VCC Range
Device
Voltage Reference
1
1, 2, 4
1
TC7650
MCP601
2
TC913A
TC7652
# per Package
Device
Operational Amplifiers
–
–
–
–
Development Tools
–
–
–
–
Development Tools
–
Development Tools
–
–
–
–
–
–
–
–
–
–
–
Development Tools
Temperature Sensor Design Guide
SELECTED PRODUCT SPECIFICATIONS
16
Temperature Sensor Design Guide
ANALOG AND INTERFACE PRODUCTS
Stand-Alone Analog and Interface Portfolio
Thermal
Management
Power
Management
Linear
Mixed-Signal
Temperature
Sensors
LDO & Switching
Regulators
Op Amps
Fan Speed
Controllers/
Fan Fault
Detectors
Charge Pump
DC/DC Converters
Programmable
Gain
Amplifiers
Digital
Potentiometers
Power MOSFET
Drivers
Comparators
D/A Converters
PWM Controllers
Linear
Integrated
Devices
V/F and F/V
Converters
System Supervisors
Voltage Detectors
A/D Converter
Families
Interface
CAN Peripherals
Infrared
Peripherals
LIN Transceiver
Serial Peripherals
Ethernet Controller
Energy
Measurement
ICs
Voltage References
Battery
Management
Li-Ion/Li-Polymer
Battery Chargers
Smart Battery
Managers
Analog and Interface Attributes
Robustness
MOSFET Drivers lead the industry in latch-up
immunity/stability
Low Power/Low Voltage
Op Amp family with the lowest power for a given gain
bandwidth
600 nA/1.4V/14 kHz bandwidth Op Amps
1.8V charge pumps and comparators
Lowest power 12-bit ADC in a SOT-23 package
Integration
One of the first to market with integrated LDO with
Reset and Fan Controller with temperature sensor
PGA integrates MUX, resistive ladder, gain switches,
high-performance amplifier, SPI interface
Space Savings
Resets and LDOs in SC70, A/D converters in a
5-lead SOT-23 package
CAN and IrDA® Standard protocol stack embedded in
an 18-pin package
Accuracy
Low input offset voltages
High gains
Innovation
Low pin-count embedded IrDA Standard stack,
FanSense™ technology
Select Mode™ operation
For more information, visit the Microchip web site at:
www.microchip.com
17
Support
Training
Microchip is committed to supporting its customers
in developing products faster and more efficiently. We
maintain a worldwide network of field applications
engineers and technical support ready to provide product
and system assistance. In addition, the following service
areas are available at www.microchip.com:
■ Support link provides a way to get questions
answered fast: http://support.microchip.com
■ Sample link offers evaluation samples of any
Microchip device: http://sample.microchip.com
■ Forum link provides access to knowledge base and
peer help: http://forum.microchip.com
■ Buy link provides locations of Microchip Sales Channel
Partners: www.microchip.com/sales
If additional training interests you, then Microchip can
help. We continue to expand our technical training options,
offering a growing list of courses and in-depth curriculum
locally, as well as significant online resources – whenever
you want to use them.
■ Regional Training Centers: www.microchip.com/rtc
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■ Resources from our Distribution and Third Party Partners
www.microchip.com/training
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1/26/09
Information subject to change. The Microchip name and logo, the Microchip logo and PIC are registered trademarks of Microchip
Technology Incorporated in the U.S.A. and other countries. FanSense, Linear Active Thermistor, PICkit, PICtail and Select Mode are
trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. All other trademarks mentioned herein are
property of their respective companies. © 2009, Microchip Technology Incorporated. All Rights Reserved.
Printed in the U.S.A. 2/09
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