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TRANSCRIPT
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IC Temperature
Sensors
Jared Bench
ECE 5320
Spring 2004
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Why IC Temperature Sensors
Limitations/Advantages
IC Temperature Sensors Explained
Types of IC Sensors
Interfacing Applications
Conclusions
Contents
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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References
Claire O'Keeffe and Brian Black, Choosing an ICTemperature Sensor http://www.electronicproducts.com/
IC Temperature Sensors Find the Hot Spots,http://www.maxim-ic.com/
Jay Scolio, Temperature Sensor ICs
Simplify Designs, Maxim IntegratedProducts, Inc.
MAX675 Data Sheet, Maxim Integrated Products, Inc.
National Semiconductors Temp Sensor Handbook,www.national.com/appinfo/tempsensors/files/temphb.pdf
National Semiconductors Analog University,www.national.com/AU/design/1,4678,18_0_,00.html
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Further Reading
List of Vendors,http://temperatures.com/semivendors.html
Introduction to Semiconductor TemperatureSensors, www.capgo.com/Resources/
Temperature/Semiconductor/Semi.html Sensor Industry Developments and Trends,
Sensor Business Digest, September 2004
Tons of Temperature Sensor Information,http://temperature-measurement.globalspec.com/
Computer Interfacing Example,http://www.iguanalabs.com/tempture.htm
http://www.temperatures.com/forum/
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Why Monitor Temperature
Monitoring Temperature is becoming
more important as electronic systems
become increasingly dense and power-hungry.
Systems are affected by temperature
extremes
Components may be damaged if the
temperature falls outside the operating
range.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Desired Sensor Characteristics
Accuracy
Practicality
Reliability
High Precision
Easy to Interface Linearity
Wide Range
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Common Temperature Sensors
Thermistors
Resistance Temperature Detectors
(RTDs)
Infrared (IR)
Thermocouples
IC Temperature Sensors
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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IC Temp Sensors at a Glance
Varied array of functions, features, and
interfaces.
Capabilities: Report both local and remote temperatures
Monitor other system parameters
Control fans
Warn when a specific temperature is
exceeded.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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IC Temp Sensor Advantages
Small and simple
Accurate
Inexpensive
No linearization or cold-junction compensationis required.
External or internal hot spots can be monitored.
Generally provide better noise immunitythrough higher-level output signals.
Easy to interface with other devices such asamplifiers, regulators, DSPs, and micro-controllers.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Linearity
IC Temp Sensors are highly linear. The linearity of thermistors and Si temp
sensors is contrasted below.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim
Integrated Products
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IC Temp Sensor Limitations
The use of IC temperature sensors
is limited to applications where the
temperature is within a55 to150C range.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Principle of IC Temp Sensors
Operation of IC temperature
sensors is based on the behavior of
silicon PN junctions as a function oftemperature.
Introduction
Limitations &
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Working
Principles
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Interfacing
Applications
Conclusions
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IC Temperature Sensor Theory
A current is forced through two PN
junctions with different active areas.
The difference between the forwardvoltages on the two junctions is
proportional to absolute
temperature: V1 - V2 = (kT/q) ln(J1/J2)
Introduction
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Interfacing
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IC Temperature Sensor Theory
V1 - V2 = (kT/q) ln(J1/J2)
Thus the difference in forward
voltage is directly proportional toabsolute temperature
Introduction
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Working
Principles
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Interfacing
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With accurate forcing of the two
current levels, temperature can be
calculated from a measured VBEalmost without regard to the initial
forward voltage, physical size of the
junction, leakage, or other junctioncharacteristics.
IC Temperature Sensor Theory
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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The excessive leakage currents
characteristic of silicon PN
junctions limits the temperature forIC-based sensors to about 200C.
These currents double with every
10C rise in temperature, causingmalfunctions in bandgap references
and signal-conditioning circuitry.
IC Temperature Sensor Theory
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
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Types of IC Temp Sensors
Classified according to the input sourceand output-signaling method.
Two main types of IC temperature
sensors: Analog
Produce a voltage or current proportional totemperature
Digital Include an integrated A/D converter Can include other features such as voltage
monitoring, fan control, and over or under limitalarms.
Introduction
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Working
Principles
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Interfacing
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Representative Temperature Sensors
Device Measures Output Interface Package Comments
Analog Devices AD590 Package temperature Analog current SO-8
Very stable, immune to line-
voltage drops in
remote sensing, good
noise immunity
Maxim MAX675, REF-01,
LM45, Analog Devices
AD22103
Package temperature Analog voltage SO-8 or SOT-23
Often combined with a voltage
reference or other
building blocks, shunt
and buffered-VOUT
types available
TMP01, TC620, Maxim
MAX6502Package temperature
Thermostat logic
outputSOT-23
Built-in analog comparators,
usually with adjustable
hysteresis
Dallas Semiconductor DS1621,National
Semiconductor, LM75
and LM78, Linear
Technology LT1392
Package temperatureSerial digital
interfaceSO-8, SO-16
I2C, SPI, SMBus interfaces;sometimes built into
large, multifunction
A/D-converter ICs
Maxim MAX1617 Remote diode junctionSerial digital
interface16-pin QSOP
SMBus interface; monitors
CPU temperatures
directly
Introduction
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Working
Principles
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Interfacing
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Analog Sensors An ideal analog sensor provides an
output voltage that is a perfectly linearfunction of temperature
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Images: Maxim Integrated Products
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Analog Plus Sensors
"Analog Plus" sensors are available withvarious types of digital outputs.
The "plus" added to the analog temperature
sensor can be a comparator such that logicoutput trips when temperature passes a presetthreshold.
Other types of "plus" sensor relay temperaturedata in the form of the delay time after the parthas been strobed, or in the form of thefrequency or the period of a square wave.
Introduction
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Working
Principles
Sensor Types
Interfacing
Applications
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Digital I/O Sensors
Digital temperature data is passed to themicrocontroller, usually via a serial bus.
Data is sent to the temperature sensor
from the microcontroller along the samebus, usually to set the temperature limitat which the alert pin's digital output willtrip.
An interrupt is sent to the microcontrollerwhen the temperature limit has beenexceeded.
May also provide fan control.
Introduction
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Working
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Interfacing
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System Monitor Sensors
In addition to the functions provided by thedigital I/O type, this type of device commonlymonitors the system supply voltages, providing
an alarm when voltages rise above or sinkbelow limits set via the I/O bus.
Fan monitoring and/or control can also beincluded in this type of IC.
In some cases, this class of device is used todetermine whether a fan is working. Morecomplex versions control the fan as a functionof one or more measured temperatures.
Introduction
Limitations &
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Working
Principles
Sensor Types
Interfacing
Applications
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Types of Interfaces
Interfaces include:
Single wire Pulse Width Modulation (PMW)
Two wire I2
C and SMBus Used mostly in PC and communications
applications
Three or four wire SPI protocols.
Serial interface common in non-PC environments
Can also be bi-directional
Microcontroller gives instructions to the
temperature sensor.
Introduction
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Working
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Interfacing
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Applications
Remote Temperature Monitor Measures two temperatures
Local Temperature
Temperature of a remote location using a diode
connected transistor Very useful in space constrained applications
May be integrated on a microprocessor chip
Eliminates the inaccuracy that results from a thermalresistance path between the sensor and chip.
Facilitates the ability to increase clock speed withoutexceeding thermal capabilities.
Can be used as a sensor for clock throttling.
Used in almost every electronic system larger than apager.
Introduction
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Working
Principles
Sensor Types
Interfacing
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CPU Temperature Sensor
A user-programmable temperaturesensor monitors the temperature ofa remote CPU's on-chip PN
junction.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim
Integrated Products
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Remote Temperature Sensor
This user programmable temperature sensorcan monitor its own local temperature and the
temperatures of four remote PN junctions.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim
Integrated Products
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Distributed Temperature Sensing
Here a microcontroller strobes eighttemperature sensors connected on a commonline and receives the temperature datatransmitted from each sensor on the same line.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim Integrated Products
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Applications
Monitoring systems
Systems requiring thermal
monitoring and control may requiremonitoring of other system
parameters
Power supply
Internal voltages and currents
DC offsets of critical signals.
Introduction
Limitations &
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Working
Principles
Sensor Types
Interfacing
Applications
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Digital Fan Controller
A fan controller/temperature sensor IC can useeither a PWM or a linear mode control scheme.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim
Integrated Products
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Analog Plus Heater Controller
A temperature sensor can transmit a squarewave whose frequency is proportional totemperature as part of a heater controllercircuit.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim
Integrated Products
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Digital Over-Temp Indicator
This sensor can
signal when a
temperature hasbeen exceeded
Well suited for:
Over or under-temperature alarms
On/off fan control.
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions
Image: Maxim Integrated Products
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Conclusions
IC Temperature Sensors:
Are small and inexpensive
Have desirable sensor characteristics
Are available in many interface types
Can be easily integrated into existing
systems Have many practical applications
Introduction
Limitations &
Advantages
Working
Principles
Sensor Types
Interfacing
Applications
Conclusions