2004 APPLICATION NOTE 3178 Extended-Range Temperature-Sensin

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2004 APPLICATION NOTE 3178 Extended-Range Temperature-Sensin

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Maxim Notes AUTOMOTIVE CIRCUIT PROTECTION TEMPERATURE SENSORS THERMAL MANAGEMENT Keywords: MAX6627, MAX6646, MAX6647, MAX6649, MAX6642, MAX6692, extended-range, temperaturesensing,
2004
APPLICATION NOTE 3178
Extended-Range Temperature-Sensing
Abstract: Using remote temperature sensors monitor temperature high-performance microprocessors graphics processors common technique managing power thermal operating characteristics. clock speeds, circuit densities, power levels increase, operating temperatures exceed limits conventional temperature sensors. temperature sensors from Maxim measure temperatures previously beyond range such devices. This article discusses extended-range temperature sensors, their theory, applications. Digital, remote temperature sensors that external bipolar transistor sensing element widely relied monitoring temperature high-speed, high-performance like microprocessors, graphics processors, FPGAs. Monitoring temperature accurately critically important ensuring best performance protecting against catastrophic failure. temperature monitor lets system perform control clockthrottling functions keep high-performance within necessary operating temperature ranges. higher temperatures, used shut system down prevent failure. performance power levels increase, remote temperature-monitoring function becomes even more important, more difficult perform. Virtually conventional digital temperature-sensor have upper measurement limits less than 128°C; many limited 100°C. Frequently, conventional temperature range sufficient. However, there times when important measure temperatures high 150°C. such cases, extended-range temperature sensors necessary.
Sensing Extended Temperatures
typical digital temperature-sensor represents temperature data using sign seven magnitude bits with 64°C. Although some digital sensors have additional bits express temperature with more resolution, 64°C limits highest measured temperature less than 128°C. extended-range temperature sensor measure values well above this 128°C limit-often high 150°C. most convenient performing this task providing with weight 128°C. this case, temperature data range extends 255°C, which well beyond useful range unlikely that temperatures over 127°C will encountered. Accuracy degrades rapidly temperatures above approximately 150°C because limitations semiconductor junctions used measure temperature. maximum operating temperature some highpower depends clock speed, process, device package, various design factors. Often, signal integrity degrades with increasing temperature until circuit longer meets specifications. many CPUs graphics processors, this happens around 100°C; some high-performance circuits, normal operation extend 145°C. device function properly extended temperature, accurately measuring temperature important keeping within correct operating range. Since absolute maximum temperature near this range, even more critical monitor temperature avoid failure subsequent shutdown (Figure
Figure Extended-range remote temperature sensors monitor highperformance devices through their full operating ranges. some high-performance processors, physics thermal diode adds "offset" measured temperature. other words, measured temperature significantly higher than real temperature. this case, temperature sensor needs measure apparent temperatures that much higher than normal operating range. Although measured temperature might 150° higher, diode's real temperature still within processor's normal operating temperature range.
Remote Temperature-Sensing Basics
most common approach measuring temperature with remote-diode temperature sensor forces different currents through diode, typically with current ratio about 10:1. (The diode two-lead device like 1N4001. Instead, diode-connected bipolar transistor. ideality factor two-lead diode incompatible with remote-diode temperature sensors.) diode's voltage measured each current level temperature calculated based equation,
where: larger diode bias current smaller diode bias current diode voltage caused diode voltage caused ideality factor diode Boltzmann's constant (1.38 10-23joules/°K) temperature charge electron (1.60 10-19°C) =10, this simplified
term called ideality factor processdependent. value quite close most transistors. example, Pentium® microprocessors have ideality factor about 1.008, while Pentium microprocessors about 1.002. remote-diode temperature sensor generates currents with precise ratios, measures resulting voltages, then scales level-shifts voltage measurement produce temperature data. internal analog-to-digital converter (ADC) must able accurately measure small voltages with rather large common-mode values; temperature change corresponds approximately 200µV. extended-range temperature sensor similar conventional sensor, with slightly larger inputvoltage range accommodate larger voltage differentials between high current levels. Also, temperature data must organized differently. Maxim's extended-range temperature sensors higherweighted permit temperature measurements above 128°C. This usually done replacing sign with larger MSB. produce reliable, accurate, extended-range remotediode temperature sensor, precise manufacturing test techniques must employed trim sensor verify accuracy. Maxim's proprietary thermalmanagement test systems measure temperature sensor thermal diode trim sensor's internal circuitry accuracy that unmatched industry.
Remote Temperature Sensors Measure 150°C
Maxim's first extended-range remote temperature sensor MAX6627, introduced 2001. MAX6627 unique among remote temperature sensors because 3-wire (clock, serial data out, chip select) digital interface. available small, 8-pin SOT-23 package, which allows located near critical components. 2003, Maxim introduced MAX6646/MAX6647/ MAX6649, three extended-range remote temperature sensors with 2-wire, interface, which makes them particularly well suited desktop, notebook, server applications. These sensors have accuracy 145°C (Figure making them world's most accurate extended-range temperature sensors. They pin-compatible with industrystandard MAX6692, register-compatible well. However, 128°C above, temperature data registers have additional data allow higher temperature measurements. These sensors also include features such thermal comparator outputs indicate over- undertemperature conditions, which useful monitoring protecting high-performance ICs.
Figure MAX6649 measures thermal diodes CPUs graphics processors with accuracy from 60°C 145°C. Temperatures 150°C measured with reduced accuracy. Another extended-range sensor introduced 2003 MAX6642 (Figure smallest extendedrange temperature sensor available with SMBus interface. packaged 6-pin TDFN with footprint only 0.8mm thickness. Accuracy guaranteed within ±1°C from 60°C 100°C, ±3.5°C from 100°C 150°C.
Figure MAX6642 world's smallest remote temperature sensor, measuring temperatures 150°
Summary
Although extended-range remote temperature sensors market, their need variety current future systems clear. Maxim committed supplying highest precision extended-range sensors industry will continue introduce innovative extended-range products that keep pace with emerging system requirements.
similar article appeared January, 2004 issue magazine. Pentium registered trademark Intel Corporation SMBus trademark Intel Corp.
Application Note 3178: http://www.maxim-ic.com/an3178 More Information technical questions support: http://www.maxim-ic.com/support samples: http://www.maxim-ic.com/samples Other questions comments: http://www.maxim-ic.com/contact Related Parts MAX6627: QuickView Full (PDF) Data Sheet Free Samples MAX6642: QuickView Full (PDF) Data Sheet Free Samples MAX6646: QuickView Full (PDF) Data Sheet Free Samples MAX6647: QuickView Full (PDF) Data Sheet Free Samples MAX6649: QuickView Full (PDF) Data Sheet Free Samples MAX6692: QuickView Full (PDF) Data Sheet Free Samples
AN3178, 3178, APP3178, Appnote3178, Appnote 3178 Copyright Maxim Integrated Products Additional legal notices: http://www.maxim-ic.com/legal

2004 APPLICATION NOTE 3178 Extended-Range Temperature-Sensin

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