thermal manegement electronic

8/20/2019 Thermal Manegement Electronic

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Thermal

Management

Handbook

Revised March 2014


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Introduction: Thermal Management in Electronic Systems.................................................. 3

Temperature-Sensing Technologies........................................................................................ 4

Thermistors............................................................................................................................... 4 NTC Thermistors................................................................................................................... 4

RTDs......................................................................................................................................... 7 Thermocouples......................................................................................................................... 9 Temperature Sensor ICs......................................................................................................... 13

Analog Temperature Sensor ICs......................................................................................... 13

Local Digital Temperature Sensor ICs.................................................................................1 !ther Digital Temperature Sensor "eatures....................................................................1#

Remote Digital Temperature Sensors................................................................................. $1 Remote Temperature Sensor %rror Sources................................................................... $3 !ther Remote Sensor "eatures...................................................................................... $

Other Types of Thermal Management Components............................................................. !

Temperature S&itches............................................................................................................ $# "an Spee' Controllers............................................................................................................ 31

T(pes o) "ans...................................................................................................................... 3$ Controlling "an Spee'.........................................................................................................34

*inimi+ing the %))ects o) "an Spee' Control on Acoustical Noise.....................................37

*onitoring "an Spee'......................................................................................................... 37 Close',Loop R-* Control.................................................................................................. 41 "an Controller Temperature Sensing.................................................................................. 4$

Close',Loop Temperature,/ase' 0Thermal Close',Loop "an Spee' Control.............4$ Loo2up Tale *apping o) Temperature an' "an Drie...................................................4$ 5No,*C6 "an Control.....................................................................................................4$

Signal Con'itioners )or Non,IC Temperature Sensors........................................................... 44 Thermistor Con'itioners...................................................................................................... 44 RTD Con'itioners................................................................................................................ 48 Thermocouple Con'itioners................................................................................................ 4

"sing Thermal Management Components#$rinciples and %pplication Circuits.............4!

Sensing Location The :e( to Choosing the Right Sensor T(pe............................................4# Remote Dio'e Sensor ;ui'elines.......................................................................................... 83

-C /oar' La(out ;ui'elines )or Remote Sensors..............................................................83 Thermal Dio'e Design ;ui'elines...................................................................................... 88

Application %i'th,*o'ulate' "an -o&er,Suppl( Drie..............................................................7= 4,>ire "an Drie................................................................................................................. 71 Conerting ->* Control Signals to Linear "an Drie........................................................7$ Linear "an Drie.................................................................................................................. 74

?igh,@oltage "an Control........................................................................................................74 4#@ 4,>ire "an Spee' Control.......................................................................................... 78 4#@ ->* -o&er Suppl( "an Spee' Controller.................................................................78 4#@ Linear "an Spee' Controller....................................................................................... 7

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!n!)) "an Control Circuits.....................................................................................................77 /asic !n!)) "an Controllers 6sing Temperature S&itches............................................... 77 Simple T&o,Spee' "an Controller..................................................................................... #= "an "ail,Sa)e Circuit............................................................................................................#1

Temperature S&itches............................................................................................................ #$ In,Circuit Temperature S&itch Testing.................................................................................#$ Thermal Cro&ar.................................................................................................................#$

%dditional &esources.............................................................................................................. !4

Application Notes Tutorials an' Re)erence Designs............................................................ #4

$


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Introduction: Thermal Management in Electronic SystemsThermal management in electronic s(stems is 'one )or one or more o) the three purposesoutline' elo&.

'.

Control Temperature 'ata is an input to a large numer o) control s(stems. The controls(stem ma( e as simple as an ono)) thermostatic controller )or room temperature

&hich actiates a heater &heneer the temperature 'rops elo& a speci)ic threshol'. !rit ma( e a comple< )an spee' control s(stem that uses measure' temperature toa'Bust the spee's o) seeral )ans to ensure a'euate cooling o) s(stem components&hile changing )an spee's in such a &a( as to minimi+e the au'iilit( o) the changes.

.

Cali(ration Temperature 'ata is use' to correct temperature,'epen'ent errors in acomponent. Caliration )unctions can e implemente' simpl( using an analogtemperature sensor &ith an operational ampli)ier circuit or the( ma( e much morecomple< &ith a loo2up tale that proi'es a 1$,it correction )actor eer( 8C )or a 'ataacuisition s(stem. "or e


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Temperature-Sensing TechnologiesThermal management egins &ith the measurement o) temperature. *a


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(a �

(b

Figure !. Resistance vs. temperature curves for a standard "TC . "ominal resistance is 1#$ at

%!&'C. "ote the nonlinearit and large relative temperature coefficient of curve (a. Curve (b isbased on a logarithmic scale and also e)hibits significant nonlinearit.

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Note that the nonlinearit( o) NTCs intro'uces a 'i))icult( &hen a &i'e range o) temperaturesmust e measure'. /ecause the slope o) the cures in "igure $ 'ecreases signi)icantl( attemperature e


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&T+sResistance temperature 'etectors 0RTDs are resistors &hose resistance aries &ithtemperature. -latinum is the most common most accurate &ire material platinum RTDs arere)erre' to as -t,RTDs. Nic2el copper an' other metals ma( also e use' to ma2eRTDs.-latinum RTD characteristics inclu'e a &i'e temperature range 0up to roughl( #==Ce


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Figure 0. T1## RTD resistance vs. temperature. Also shown is the straight-line appro)imation for# °C to %1## °C.

Figure &. T1## nonlinearit compared to linear appro)imation based on the slope from # °C to%1## °C.

Signal con'itioning )or a simple $,&ire RTD usuall( consists o) a precision resistor connecte'in series &ith the RTD a current source that )orces current through the RTD an' the precisionre)erence resistor an' a high,resolution ADC. The oltage across the re)erence resistor is there)erence oltage )or the ADC. The ADCFs conersion result is simpl( the ratio o) the RTDFs

#


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resistance to the re)erence resitance. An e


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Ta(le '. Characteristics of some common thermocouple types.

TypeTemperature

&ange/C0Short Term1

*ominalSensiti2ity

5/C1Conductor %lloys

6 7'!8 to 9'388 4'

Chromel 8; *i< '8; Cr1

%lumel ,; *i< ; Mn< ; %l< and '; Si1

= 7'!8 to 9!88 ,,'88; )e

Constantan ,,; Cu< 4,; *i1

* 7>8 to 9'388 3*icrosil !4.'; *i< '4.4; Cr< '.4; Si< 8.'; Mg1

*isil ,.; *i< 4.4; Si1

& 7,8 to 9'>88 '8!>; $t< '3; &h

'88; $t

S 7,8 to 9'>,8 '88; $t< '8; &h

'88; $t

? 8 to 9'!8 '8>8; $t< 38; &h

4; $t< ; &h

T 7,8 to 9488 43'88; Cu

Constantan

E 748 to 988 !Chromel

Constantan

)igure > sho&s the output oltage s. temperature )or a t(pe : thermocouple. The cure isreasonal( linear although it clearl( has signi)icant 'eiations )rom asolute linearit(. )igure !sho&s the 'eiation )rom a straight,line appro


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Figure /. Tpe 4 thermocouple output voltage vs. temperature. �

Figure 5. Tpe 4 thermocouple deviation from a straight-line appro)imation. �

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*easuring temperature &ith a thermocouple is some&hat 'i))icult ecause the output o) thethermocouple is lo&. It is also complicate' ecause a''itional thermocouples are create' atthe point &here the thermocouple &ires ma2e contact &ith the copper &ires 0or traces thatconnect to the signal con'itioning circuitr(. This point is calle' the col' Bunction 0see )igure .

Figure 6. 3imple thermocouple circuit. The 7unction between metal 1 and metal ! is the mainthermocouple 7unction. 8ther thermocouples are present where the metal 1 and metal ! wires 7oin

with the measuring devices copper wires or C9 traces.

The net e))ect is that the output oltage o) this circuit appears to e the oltage 'ue to thethermocouple minus the oltage o) a similar thermocouple at the col' Bunction temperature.There)ore i) the thermocouple is at H8$8C an' the col' Bunction is at H$8C @!6T &ill in'icateH8==C. To correct )or this error (ou must measure the col' Bunction temperature an' a'' thattemperature to the alue in'icate' ( @!6T

@!6T @TC , @CO@TC @!6T H @CO

This is 'one ( placing a temperature sensor at the col' Bunction location an' using themeasure' temperature to compensate )or the col' Bunction temperature. A completethermocouple,to,'igital circuit might loo2 li2e the one in )igure '8. A precision op amp an'precision resistors proi'e gain to the thermocouple output signal. A temperature sensor at thecol' Bunction location is monitore' to correct )or col' Bunction temperature an' an ADCproi'es output 'ata at the resolution reuire'. In general caliration is necessar( to correct)or ampli)ier o))set oltage as &ell as resistor temperature sensor an' oltage re)erenceerrors an' lineari+ation must e per)orme' to correct )or the e))ect o) the thermocoupleFsnonlinear temperature,oltage relationship.

1$


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igure 1#. :)ample of a thermocouple signal-conditioning circuit.

*a


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n the i'ealit( )actor 0also calle' 5noni'ealit( )actor o) the transistor Bunction 'epen's onprocess an' 'eice 'esign an' is generall( er( close to 1.=1

2 /olt+mannFs constant 1.3#=8=3 P 1= ,$3 m$ 2g s,$ :,1

the electron charge 1.=$174 P 1= ,19 coulomsT temperature in : 0temperature in C H $73.18

Figure 11. Conceptual circuit showing how two matched transistors can sense temperature.

-ractical 'esigns inclu'e trim capailities an' compensation )or noni'eal ehaior o) the circuitelements.

)igure ' sho&s a cure o) output oltage s. temperature )or a t(pical analog temperaturesensor the *AE=8. Note that the cure is uite linear. )igure '3 sho&s the 'eiation )rom astraight line )or this sensor. "rom =C to H#8C the linearit( is &ithin aout M=.$C &hich isuite goo' compare' to thermistors RTDs an' thermocouples.

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Figure 1!. 8utput voltage vs. temperature for the +A;22#& analog temperature-sensor #.!'C.

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Analog temperature sensors can hae e


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(a �

(b

Figure 10. 9loc$ diagrams of local digital temperature sensors. (a 3imple sensor with serial digital

output. (b 3ensor with additional functions, such as over-?undertemperature alarm outputs and user::R8+.

Digital temperature sensors are aailale &ith guarantee' accurac( as goo' as M=.8C oer a&i'e temperature range. !ne a'antage o) using a 'igital temperature sensor is that all o) theerrors inole' in 'igiti+ing the temperature alue are inclu'e' &ithin the sensorFs accurac(speci)ications. In contrast an analog temperature sensorFs speci)ie' error must e a''e' tothat o) an( ADC ampli)ier oltage re)erence or other component that is use' &ith the sensor.

A goo' e


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&hich achiees M=.8C accurac( across a &i'e temperature range o) ,4=C to H1=8C. !eran een more eith the correct alues store' in the N@* threshol' registers theoertemperature 'etection )unction egins to operate imme'iatel( upon po&er,up &ith nonee' )or the master to &rite to the sensor.

Interfaces Digital temperature sensors are aailale &ith a &i'e ariet( o) 'igital inter)acesinclu'ing I$C S*/usQ S-IQ 1,>ire an' ->*.

IC5SM?us Timeout In s(stems using either I$C or S*/us to communicate &ith thetemperature sensor communications errors can cause a slae to hol' the us lo& an' preenteither the master or other slaes )rom using the us. A solution o)ten inclu'e' in slae ICs li2etemperature sensors is 2no&n as 5timeout. A timeout circuit monitors the us an' &hen the'ata us has een hel' in a lo& state )or more than 38ms )or ehen it is necessar( to measureair temperature 0as oppose' to the temperature o) a oar' or an e


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Ta(le 3. Ma@imAs Docal +igital Temperature Sensors

$art +escription Interface%ccuracy

BHC1*on2olatile

MemoryCC &ange

1

+S'8 +igital thermometer and thermostat 3-Gire 8., ✓ 9.> to 9,.,

+S'' +igital thermometer and thermostat -Gire 8., ✓ 9.> to 9,.,

+S'4 +igital thermometer and memory 3-Gire 8., ✓ 9.> to 9,.,

+S'igh-precision digital thermometer and

thermostat3-Gire 8., ✓ 9.> to 9,.,

+S' +igital thermometer and real-time clocF -Gire ✓ 9. to 9,.,

+S'3'igh-precision digital thermometer and

thermostat-Gire 8., ✓ 9. to 9,.,

+S'>' +igital thermometer and thermostat -Gire ' ✓ 9.> to 9,.,

+S'> +igital thermometer 3-Gire 9., to 9,.,

+S'>igh-precision digital thermometer and

thermostat3-Gire ' ✓ 9.> to 9,.,

+S'>3'igh-precision digital thermometer and

thermostat-Gire ' ✓ 9. to 9,.,

+S'>>, +igital thermometer and thermostat -Gire 9.> to 9,.,

+S'!'$rogramma(le '-Jire digital thermostat and

thermometer'-Jire ' ✓ 9.> to 9,.,

+S'! Econo '-Jire digital thermometer '-Jire ✓ 93.8 to 9,.,

+S'!, $rogramma(le resolution< '-Jire digitalthermometer Gith 4-(it I+

'-Jire 8., ✓

93.8 to 93.>

+S'!?8 $rogramma(le resolution digital thermometer '-Jire 8., ✓ 93.8 to 9,.,

+S'!S8 igh-precision digital thermometer '-Jire 8., ✓ 93.8 to 9,.,

+S!+igital thermometer Gith seKuence detect

and $IO'-Jire 8., ✓ 93.8 to 9,.,

+S8DoG-2oltage< B8.,/C accuracy digital

thermometer and thermostat-Gire 8., ✓ 9'.> to 93.,

+S>, +igital thermometer and thermostat -Gire 9.> to 9,.,

+S>,DDoG-2oltage digital thermometer and

thermostat-Gire 9'.> to 93.>

+S>,D+igital thermometer and thermostat Gith

e@tended addressing-Gire 9'.> to 93.>

+S>,8,igh-precision< +S>,-compati(le digital

thermometer and thermostat-Gire 8., ✓ 9'.> to 93.>

DM>,+igital temperature sensor and thermal

Gatchdog-Gire 93.8 to 9,.,

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$art +escription Interface%ccuracy

BHC1*on2olatile

MemoryCC &ange

1

M%,>,Temp sensor Gith single-Gire time-delay

interface'-Gire 4., 9.> to 9,.,

M%,> Temp sensor Gith single-Gire period output '-Gire 4., 9.> to 9,.,

M%,>>Temp sensor Gith single-Gire freKuency

output'-Gire 3., 9.> to 9,.,

M%, ILC< -(it temp sensor -Gire 93.8 to 9,.,

M% ILC< '-(it temp sensor -Gire 93.8 to 9,.,

M% '-(it 9 sign digital temp sensor 3-Gire ' 93.8 to 9,.,

M%38 '-(it 9 sign digital temp sensor 3-Gire ' 93.8 to 9,.,

M%3' '-(it 9 sign digital temp sensor 3-Gire ' 93.8 to 9,.,

M%3 '-(it 9 sign digital temp sensor 3-Gire ' 93.8 to 9,.,

M%33'-(it 9 sign ILC temp sensor Gith 4 ILC

address pins-Gire '., 93.8 to 9,.,

M%34'-(it 9 sign ILC sensor Gith 3 address pins

and user-programma(le thresholds-Gire '., 93.8 to 9,.,

M%3,'-(it 9 sign ILC sensor Gith address pins

and user-programma(le thresholds-Gire '., 93.8 to 9,.,

M%,Temperature sensor and 4-channel 2oltage

monitor-Gire 3 9.> to 9,.,

M% '-(it 9 sign S$I temp sensor 3-Gire ., 93.8 to 9,.,

M%!3 Temperature sensor and 4-channel 2oltagemonitor -Gire 4 9.> to 9,.,

M%>,88+igital temp sensor and thermal Gatchdog ILC

(us Gith timeout0 DM>, compati(le-Gire 93.8 to 9,.,

M%>,8'5M%>,8

+igital temp sensors and thermal GatchdogILC (us Gith timeout and reset

-Gire 93.8 to 9,.,

M%>,835M%>,84

+igital temp sensors and thermal GatchdogILC (us Gith reset

-Gire 93.8 to 9,.,

M%3'>+igital thermometer and thermostat Gith

S$I53-Jire Interface3-Gire5

S$I ✓ 9'.> to 93.>

M%3'>3+igital thermometer and thermostat Gith

S$I53-Jire Interface3-Gire5

S$I8., ✓ 9'.> to 93.>

M%3'>, B8.,/C Docal Temperature Sensor -Gire 8., 9., to 93.>

M%3'!8 '-Jire %m(ient Temperature Sensor '-Jire 8., ✓ 93.8 to 93.>

M%3'!'-Jire +igital Temperature Sensor Gith '6(

DocFa(le EE$&OM'-Gire 8., 93.8 to 93.>

$=


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&emote +igital Temperature Sensors

A remote 'igital temperature sensor also calle' a remote sensor or a thermal 'io'e sensormeasures the temperature o) an e


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Figure 12. 3implified bloc$ diagram of a remote diode temperature sensor.

The ias current through the transistor alternates et&een current sources I1 an' I$ an' the ADC measures the resulting @/% &hile each current alue )lo&s. As e)ore the 'i))erence

et&een the t&o @/% alues is 'irectl( proportional to asolute temperature.

@/%$ , @/%1 n02Tln0IC$IC1

>hat is the a'antage o) measuring the 'ie temperature o) an e


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Figure 1/. Comparison of the behavior of a local sensor and a remote sensor. "ote that, when ane)ternal


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@/%$ , @/%1 n02Tln0IC$IC1

I) the series resistance euals 1J the 1==A an' 1=A ias currents &ill cause oltage 'ropsacross the resistor eual to 1==@ an' 1=@ respectiel( resulting in a oltage 'i))erence o)9=@. Rearranging the aoe euation an' assuming n 1 &e can see that this &ill cause anapparent temperature shi)t o)

T 0 < 9=@2 < ln01=U =.48C

*ost *ahere

T temperature in :nS%NS!R i'ealit( )actor )or &hich the sensor is optimi+e'nDI!D% i'ealit( )actor o) the 'io'e (ou are using

As an e


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The resulting error is there)ore appro


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Figure 15. Three samples of a 0&nm microprocessor with beta #.* measured using conventional+A;226!B remote temperature sensors. "ote the low errors even without beta compensation.

Other &emote Sensor )eatures

As &ith local 'igital sensors remote temperature sensors can inclu'e a ariet( o) other use)ul)eatures summari+e' elo&

O2ertemperature Outputs Nearl( all remote temperature sensors inclu'e at least oneoertemperature output an' most inclu'e t&o or more. !ne o) these outputs is t(picall( aninterrupt 0or S*/us alert that ma( also in'icate prolems such as shorte' or open,circuit'io'es. !ther outputs are most o)ten oertemperature comparator outputs.

Interfaces *ost remote temperature,sensor ICs on the mar2et &ere 'eelope' )or -Capplications an' there)ore )eature an S*/usI$C,compatile inter)ace. A )e& are aailale&ith other serial inter)aces. %


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Offset &egisters Some remote sensors inclu'e o))set registers that can a'' an o))set to themeasure' temperature. This o))set can e use' to compensate )or an error such as might ecause' ( series resistance or a transistor i'ealit( )actor &hich can a))ect the reporte'temperature alue. In the asence o) an o))set register the microcontroller 0C that rea's thesensor 'ata can a'' an o))set as nee'e'.

Ideality )actor &egisters The maBorit( o) sensing transistors use' &ith remote sensors haei'ealit( )actors that )all &ithin a relatiel( narro& range. >hen the i'ealit( )actor is outsi'e o)that range correcting )or the resulting error in reporte' temperature is relatiel( simple. Tosimpli)( this )urther a )e& remote sensors also inclu'e registers that allo& the i'ealit( )actortarget alue to e selecte' to match the i'ealit( o) the sensing transistor.

+ata %2eraging Transient noise in the s(stem can sometimes cause remote 'io'emeasurement errors. There are arious &a(s to counteract this e))ect. *a


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$art +escription&emote

ChannelsDocal

ChannelsInterface

%ccuracyBHC1

%larmOutputs

&esistanceCancellation

M%4Remotelocal sensor &ithH1$8C 'e)ault e7,channel precisiontemperature monitor

1 $,&ire 1 $ Channel 1

M%!7,channel precisiontemperature monitor 03remote 1 local 3 thermistor

1 $,&ire 1 $ Channel 1

M%8,channel precisiontemperature monitor

4 1 $,&ire 1 $ Channel 1

Other Types of Thermal Management ComponentsThermal management inoles more than simpl( sensing temperature. Seeral 2in's o)

components use temperature 'ata to per)orm a )unction such as temperature threshol''etection 0in temperature s&itches )an control or sensor signal con'itioning. Some o) theseare 'iscusse' elo&.

Temperature SGitches A temperature s&itch respon's to temperature e


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applications. The( can operate in'epen'ent o) other components an' &hen anoertemperature eent is 'etecte' can act to protect the s(stem ( )or e


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Ta(le ,. Ma@imAs Temperature SGitches

$art +escription SensorOutputType

Output$olarity

%ccuracyB/C<ma@1

+S88Resistor,a'Bustale threshol' precisiontemperature sensor t&o outputs

Local !pen 'rain 1 high 1 lo& =.8

M%,8'

"actor( threshol's )rom H38C to H1$8C in

1=C increments Local !pen 'rain Lo&

M%,8"actor( threshol's )rom H38C to H1$8C in1=C increments

Local -ushpull ?igh

M%,83"actor( threshol's )rom ,48C to H18C in1=C increments

Local !pen 'rain Lo&

M%,84"actor( threshol's )rom ,48C to H18C in1=C increments

Local -ushpull ?igh

M%,8,$ outputs 0ALAR* >ARN )actor(threshol's )rom ,4=C to H1$8C in 8Cincrements

Local !pen 'rain Lo& 3.8

M%,8$ outputs 0ALAR* >ARN )actor(threshol's )rom ,4=C to H1$8C in 8Cincrements

Local -ushpull ?igh 3.8

M%,8>$ outputs 0!@%R !: )actor( threshol's

)rom ,4=C to H1$8C in 8C increments

Local !pen 'rain Lo& 3.8

M%,8!$ outputs 0!@%R !: )actor( threshol's)rom ,4=C to H1$8C in 8C increments

Local -ushpull ?igh 3.8

M%,8 Resistor,programmale temperature s&itch Local !pen 'rain Lo& 4.7

M%,'8Resistor,programmale temperature s&itchopen,'rain an' push,pull

Local Selectale Selectale 4.7

M%,''*easure remote temperature )rom H4=C toH1$8C in 1=C )actor(,programme'increments

Remote -ushpull Lo& 8

M%,'*easure remote temperature )rom H4=C toH1$8C in 1=C )actor(,programme'increments

Remote !pen 'rain Lo& 8

M%,'3*easure remote temperature )rom H4=C toH1$8C in 1=C )actor(,programme'increments

Remote -ushpull ?igh 8

M%,'4"actor(,set threshol's )rom ,48C to H118Cin 1=C increments

Local !pen 'rain Lo& $.8

M%,',"actor(,set threshol's )rom ,48C to H118Cin 1=C increments

Local -ushpull ?igh $.8

M%,'"actor(,set threshol's )rom ,48C to H118Cin 1=C increments analog output

Local-ushpull

analog?igh $.8

M%,'>"actor(,set threshol's )rom ,48C to H118Cin 1=C increments analog output

Local!pen 'rain

analogLo& $.8

M%,'!"actor(,set threshol's )rom ,48C to H118Cin 1=C increments analog output

Local-ushpull

analog?igh $.8

M%,'"actor(,set threshol's )rom ,48C to H118Cin 1=C increments analog output

Local!pen 'rain

analogLo& $.8

M%!, Dual,output remote,Bunction s&itch Remote!pen 'rain

pushpullLo& high 1.8

M%! Dual,output remote,Bunction s&itch Remote !pen 'rain Lo& 1.8

M%!>Dual,output H4=C to H118C local an'H1$=C to H1$8C remote,Bunction s&itch

Remotelocal

!pen 'rain Lo& 3

M%!!Dual,output H4=C to H118C local an'H1$=C to H1$8C remote,Bunction s&itch

Remotelocal

-ushpull ?igh 3

3=


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)an Speed Controllers"ans are use' in electronic s(stems that reuire air )lo& to proi'e su))icient cooling )or thearious components. I) (ou use a )an 0or multiple )ans that can moe enough air to su))icientl(cool the s(stem components un'er &orst,case con'itions 0ma o) input po&er. A )anspinning at )ull spee' &hen that spee' is not nee'e' is &asting po&er increasing operatingcosts an' a''ing to the euipmentFs caron )ootprint. Re'ucing )an spee' &hen less coolingis nee'e' can re'uce the po&er &aste resulting in lo&er costs an' lo&er oerall caron'io* signal &hose 'ut( c(cle controls the spee' o) the )an.

Monitoring of )an Speed Normall( 'one ( monitoring the )anFs tachometer or 5TAC?output this metho' utili+es an output that pro'uces a speci)ic numer o) pulses per reolution.Sometimes this is 'one ( monitoring the )anFs suppl( current although this is much lessreliale.

31


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+etecting )an )ailure This is usuall( 'one as part o) the )an spee' monitoring process. Itcan also e 'one ( )ans that hae 5)ail or 5loc2e' rotor outputs instea' o) TAC? outputs.*onitoring the spee' o) a )an &hen 'rien to its )ull spee' also allo&s 5pre'ictie )an,)ailure'etection. As )ans near en',o),li)e the( can egin to slo& 'o&n. /( 'etecting thisphenomenon a s(stem can ensure that a )an near the en' o) its use)ul li)etime is replace'e)ore )ailing completel(.

Closed-Doop Control of )an Speed This is a comination o) )an spee' control an'monitoring. /( monitoring the )anFs tachometer signal the spee' o) the )an can e a'Buste' to)orce it to a 'esire' alue 0e.g. 3==R-*.

Ensuring DoG %udi(ility of Speed Control A'Busting the spee' o) a )an to match thes(stemFs cooling reuirements can help to re'uce the aerage noise leel pro'uce' ( the )an.?o&eer it is necessar( to e a&are that each time the )anFs spee' is change' the change innoise leel can e er( apparent to an(one near the s(stem. The est )an,control ICs inclu'e)eatures that help to re'uce the au'iilit( o) )an spee' changes.

Monitoring of Temperature The )an controller can inclu'e one or more channels o)

temperature sensing.

Temperature-?ased )an Speed Control Temperature 'ata can e use' to a'Bust )an spee'ase' on s(stem,speci)ic temperature,spee' pro)iles.

Types of )ans

The est &a( to control the spee' o) a )an 'epen's on the t(pe o) )an. /rushless DC 0/LDC)ans are the most common t(pe use' to cool electronic euipment. These )ans are aailale&ith po&er suppl( oltages o) 8@ 1$@ $4@ an' 4#@. 1$@ )ans are the most common. 8@ )ansare o)ten )oun' in portale euipment such as noteoo2 -Cs. 4#@ )ans are commonl( use' inin'ustrial an' telecommunications euipment.

There are three categories o) /LDC )ans re)erre' to ( the numer o) &ires on the )an assho&n in )igure '. The simplest is the $,&ire )an &hich Bust has po&er suppl( connections.

3$


34/89

Figure !1. !-, *-, and 0-wire fans.

A 3,&ire )an also has po&er suppl( connections plus an a''itional &ire that proi'esin)ormation aout the )anFs status. There are t&o stan'ar' )unctions )or the thir' &ire. This thir'&ire ma( e a TAC? output or a 5loc2e',rotor output.

A TAC? output is usuall( an open,'rain logic output that pro'uces a series o) pulses as the )anspins. *ost )ans pro'uce t&o pulses per reolution ut )ans pro'ucing one )our or eightpulses per reolution are also aailale. /( 'etermining the perio' or )reuenc( o) thetachometer pulses the )anFs spee' can e calculate'. This 'ata can then e use' )or close',loop control o) the )anFs R-* ( comparing the actual R-* &ith the target R-* an' thena'Busting the 'rie to the )an until the actual R-* matches the target R-*.

The tachometer signal can also e use' to 'etect )an )ailure. "or ehile less )le* spee',control input. /( ar(ing the 'ut( c(cle o) the ->* &ae)ormsupplie' to this input the spee' o) the )an can e arie' oer a range o) aout 3=V to 1==V o)the ma


35/89

Controlling )an Speed

It is clear that asic spee' control is eas( to 'o &ith a 4,&ire )an. A C can generate a ->*&ae)orm as can most )an spee' controller ICs. ?o&eer 4,&ire )ans are still less commonthan $, an' 3,&ire units so the ariet( o) con)igurations is limite' relatie to the other t(pes. Insome cases the right )an )or the application is aailale onl( as a $, or 3,&ire unit. Controllingthe spee' o) a $,&ire or 3,&ire )an can e some&hat more inole' ecause these )ans 'o

not hae a 'e'icate' spee',control input. Instea' the spee' o) these )ans must e controlle'( mo'i)(ing the suppl( oltage applie' to the )ans.

I) (ou ar( a )anFs po&er suppl( oltage the )anFs spee' &ill ar(. )igure sho&s )an R-*s. )an po&er suppl( oltage )or a t(pical lo&,cost 1$@ )an. The )anFs spee' in this e


36/89

Figure !*. 3ome fan control * )an 'rie. Thisapproach can e ma'e more e))icient at a higher cost ( replacing the LD! &ith a s&itch,mo'e oltage regulator.

Figure !0. Comparison of power dissipation in linear (upper curve and + fan drive (lower curveapproaches.

38


37/89

A lo&er cost more e))icient approach is sho&n in )igure ,. In this case the )anFs po&ersuppl( is mo'ulate' ( a ->* &ae)ormGthe po&er suppl( e))ectiel( turns on an' o)) at arate o) roughl( 3=?+. /ecause the pass transistor is al&a(s either )ull( on or )ull( o)) its po&er'issipation is negligile compare' to the po&er use' ( the )an.

Figure !&. Controlling the speed of a !- or *-wire fan b pulse-width modulating the power supplusing an n-channel F:T on the low side of the fan.

6sing an n,channel *!S"%T 0or an N-N on the groun' &ire o) the )an allo&s the pass 'eiceto e 'rien ( a 3.3@ or 8@ logic,leel ->* signal. The TAC? or loc2e',rotor output is pulle'up to the )anFs po&er suppl( oltage. Alternatiel( a p,channel *!S"%T 0or a -N- can euse' on the positie po&er suppl( &ire instea'. This results in a groun',re)erre' TAC? orloc2e',rotor output ut reuires that the ->* signal s&ing up to @"AN. *a* )an spee' controllers that are compatile &ith either n,channel or p,channel )an 'rieinclu'ing the *AE18 *AE1 *AE39 *AE4= *AE41 an' *AE7#.

->* )reuencies &ell elo& 3=?+ are usuall( aoi'e' &hen using this techniue ecause as)reuencies 'ecrease there is an au'ile change in the )anFs spee' 'uring the on an' o))

perio's o) the ->* &ae)orm. As the )reuenc( increases e(on' 38?+ or so the 5on perio'can ecome too short to allo& the )anFs internal electronics to turn on an' egin 'riing the )an.

This ->* approach su))ers )rom three 'ra&ac2s. "irst some )an manu)acturers recommen'against it 'ue to concerns aout )an reliailit(. I) (ou are planning to 'rie a $, or 3,&ire )an&ith a pulse,&i'th mo'ulate' po&er suppl( e sure that the )an en'or allo&s the use o) thistechniue.

The secon' 'ra&ac2 is noise. >ith some )ans the 3=?+ pulse &ae)orm causes the )anFsmotor mechanism to moe in response to the pulses resulting in an un'esirale 5tic2ing or5clic2ing soun' emanating )rom the )an at a 3=?+ rate. This is er( au'ile &ith some )ans

though nearl( inau'ile &ith others.

The thir' 'ra&ac2 is that 'uring the 5o)) perio' o) the ->* &ae)orm the )an pro'uces notachometer pulses. There)ore )an spee' can e monitore' onl( 'uring the 5on perio'. Thiscan e a serious prolem &ith lo&,R-* )ans as the( ma( not pro'uce een a singletachometer pulse c(cle 'uring a ->* 5on perio'. There are man( 'i))erent schemes tooercome this prolem &ith oth ar(ing leels o) comple


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Minimiing the Effects of )an Speed Control on %coustical *oise

In some installationsG)or e


39/89

Figure !2. (a +onitoring fan speed b counting tachometer pulses for a period of 1s can result inlow-resolution measurements. (b Eenerating a cloc$ signal with sufficientl high fre@uenc, andthen counting the number of cloc$ pulses in a limited number of tachometer periods, provides moreresolution and allows the fans R+ to be controlled to within a tighter tolerance.

Some )an controller ICs inclu'e a )eature that allo&s spee' monitoring o) $,&ire )ans. This is'one ( a''ing a resistor et&een the s(stem groun' an' the )anFs groun' &ire. >hile the )an

motor operates its suppl( current ariations create oltage 'rops on the sense resistor that arecompare' against a re)erence oltage ( the )an controller IC. This techniue has itslimitationsGsuppl( current &ae)orms 'i))er signi)icantl( )rom )an to )an an' also ar( as )anspee' changes as sho&n in )igure >. There)ore suppl( current monitoring is moreappropriate )or 'etection o) )an )ailure than )or close',loop )an spee' control.

3#


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Figure !/. :)amples of fan suppl current waveforms. (a A fan driven with half the nominal powersuppl voltage. (b The same fan driven with the nominal power suppl voltage.

)igure ! sho&s a t(pical approach to monitoring )an spee' using a sensing resistor to sensethe )anFs suppl( current. In this circuit the ICFs internal 'etection sensitiit( is aout $8=m@.

The approach is appropriate )or linear 'rie an' ->* po&er suppl( 'rie 0either high si'e orlo& si'e.

39


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Figure !5. (a Tpical input stage for monitoring fan speed using the fans suppl current. (b singthis input stage to monitor fan speed using a !G sensing resistor.

As mentione' rie)l( in the Controlling Fan Speed section a complication arises &hen a )an is'rien ( a pulse,&i'th mo'ulate' po&er suppl(. During the portion o) the ->* &ae)orm&hen the )anFs po&er suppl( is o)) the )an cannot pro'uce tachometer pulses. "an controllerICs generall( hae an option that allo&s monitoring o) the )anFs tachometer signal onl( 'uringthe 5on portion o) the ->* &ae)orm ut there are cases in &hich the 5on perio' is too shortto allo& proper tachometer measurement.

As an e* c(cle. The )anFs internal circuitr( &ill there)ore hae onl( 1.7msaailale to generate a $8ms tachometer signal so the tachometer signal &ill not e usale.Note that a much )aster )an &oul' &or2 etter. "or e


42/89

!ne solution to this prolem is to perio'icall( increase the 5on time o) one c(cle o) the ->*&ae)orm to a 'uration that is su))icient to measure the tachometer signal. This approach&or2s ut its suitailit( 'epen's on the )an eing use'. I) the pulse nee's to e stretche'signi)icantl( the pulse stretching &ill e au'ile. Au'iilit( o) the pulse stretching 'epen's onthe 'egree o) stretching an' also on the response time o) the )an. I) the )an respon's uic2l( tosuppl( oltage changes the pulse stretching &ill e eas( to hear.

Another &a( to sole this prolem is to 2eep the )anFs po&er suppl( actie 'uring the lo&portion o) the ->* &ae)orm. )igure illustrates this 52eep,alie approach. A p,channel"%T 'ries the )anFs high si'e. A 'io'e proi'es 4.3@ 'rie to the )an &hen the ->* is o)).This 2eeps the )anFs internal IC po&ere' an' continuousl( generating the tachometer signal sothat the )anFs spee' can e monitore' een 'uring the 5o)) portion o) the ->* &ae)orm. A'isa'antage o) this circuit is that the )an is al&a(s po&ere'. I) necessar( this can e )ihen (ou can accuratel( monitor thetachometer it ecomes possile to control the )anFs R-* ( a'Busting the 'rie leel topro'uce the 'esire' tachometer )reuenc( 0or perio'. "an spee' accurac( as goo' as M1Vcan e achiee' 'epen'ing on measurement resolution an' cloc2 accurac(. Close',loop )anspee' control is aailale in seeral o) *a


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*AE39 *AE4= *AE8= *AE81 *AE= *AE1 *AE317#8 an'*AE3179=.

)an Controller Temperature Sensing

*ost )an controller ICs can sense temperature usuall( oth local an' remote. Since )ancontrol is usuall( ase' on temperature it ma2es sense in man( s(stems )or the )an controller

to e ale to measure temperature. %


44/89

Ta(le . Ma@imAs )an Control $roducts

$art +escription&emote

ChannelsDocal

ChannelsInterface

)anOutputs

Closed-Doop&$M

T%CInput

+S'>!8 $,channel C-6 peripheral monitor = 1 $,&ire 1 linear No $

M%',$,channel thermistor inputs 1 localsensor $ )an controllers

$ 1 $,&ire $ ->* No $

M%' $,channel thermistor inputs 1 localsensor $ )an controllers

$ 1 $,&ire $ ->* No $

M%8I$C ua' linear )an controller &ithR-* control

= = $,&ire 4 linear Xes 4

M%3$,channel temperature monitor &ith'ual ->* )an spee' controller )or $,3, 4,&ire )ans

1 1 $,&ire $ ->* Xes $

M%48$,channel temperature monitor &ith'ual ->* )an spee' controller )or $,an' 3,&ire )ans

1 1 $,&ire $ ->* Xes $

M%43 Automatic stan',alone )an controller 1 1-in strap

logic1 ->* No $

M%44 Automatic stan',alone )an controller $ =-in strap

logic1 ->* No $

M%4, Automatic stan',alone )an controller $ =-in strap

logic 1 ->* No $

M%,8Linear )an,spee' regulator an'monitor

= = $,&ire 1 linear Xes Xes

M%,'Linear )an,spee' regulator an' 4,)anmonitor

= = $,&ire 1 linear Xes Xes

M%,3Temperature monitors an' ->* )ancontrollers

1 1 $,&ire 1 ->* Xes Xes

M%8Remote,Bunction temperature,controlle' linear )an spee' regulator

1 = $,&ire 1 linear Xes Xes

M%'Remote,Bunction temperature,controlle' linear )an spee' regulator

1 = 3,&ire 1 linear Xes Xes

M%3Temperature monitors an' ->* )ancontrollers

1 1 $,&ire 1 ->* Xes Xes

M%4Temperature monitors an' ->* )an

controllers1 1 $,&ire 1 ->* Xes Xes

M%,"an ono)) controller'rier an'temperature s&itch &ith )actor(,programme' threshol'

= 1 -in strap 1 ono)) No No

M%>!$,channel temperature monitor &ith'ual ->* )an controller an' 8 ;-I!s

$ 1 $,&ire $ ->* No No

M%!4 "an,)ailure 'etector an' po&er s&itch = = Logic 1 ono)) No No

M%3'>48 6ltra,Simple "an,Spee' Controller1

0thermistor= NA 1 ->* No No

M%3'>!, ,Channel Intelligent "an Controller1=

0 'io'e 4$,&ire

1 $,&ire ->* Xes

M%3'>8,Channel ->*,!utput "an R-*Controller

= = $,&ire Xes ,1$

M%3'>!Thermal *anagement *icrocontroller. "an Controllers I$C *aster )or%


45/89

Signal Conditioners for *on-IC Temperature SensorsThe )inal t(pe o) thermal management pro'uct &e &ill 'iscuss &or2s &ith thermistors RTDs orthermocouples to help inter)ace those sensors to s(stems. Simpli)ie' e


46/89

"or 'i))erent thermistor,resistor cominations create a sprea'sheet to calculate the output co'e as a )unction o) temperature. )igure 3' sho&s a simpler circuit )or thermistor conersion. The *AE#$ has an input )or a single thermistor an' a oltage re)erence output to 'rie the thermistorresistor oltage 'ii'er. The 'igital 'ata is serial an' rea' onl(. As &ith the *AE9# the 'ata sheet inclu'es a tale sho&ing ho& the output co'e maps to thermistor temperature )or a common thermistor t(pe.

Figure *1. +A;225! single thermistor-to-digital converter.

&T+ Conditioners

)igure 3 sho&s the *AE31#8 a single,chip RTD,to,'igital conerter. The *AE31#8accepts a $, 3, or 4,&ire RTD an' measures its resistance relatie to that o) an e


47/89

Figure *!.The +A;*152& digities the resistance of a !-, *-, or 0-wire RTD, detects cable and sensorfaults, and includes >0& input protection.

/ecause RTDs can e locate' some 'istance )rom the signal con'itioning circuitr( their calescan sometimes e e


48/89

The *AE31#88 sho&n in )igure 33 measures the output o) % O : N R S or Tthermocouples 0separate *AE31#88 ersions are aailale )or each thermocouple t(pe as&ell as the col',Bunction temperature comines them an' presents the 'ata in C )ormat oera simple 3,&ire 0cloc2 'ata output chip select inter)ace. Thermocouple open,circuits an'shorts to suppl( an' groun' are automaticall( 'etecte'.

The *AE31#8= an' *AE31#81 are similar to the *AE31#88 ut use *aireinter)ace. This inter)ace allo&s eas( net&or2ing o) multiple thermocouples as &ell as an('esign reuiring the minimum possile numer o) con'uctors. The *AE31#8= accepts % O :N an' T thermocouples &hile the *AE31#81 accepts the lo&er,output R an' Sthermocouples.

Ta(le > summari+es *a


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Ta(le >. Ma@imAs Signal Conditioners for *on-IC Temperature Sensors

$art +escriptionSensorInputs

DocalSensors

Interface

M%83$,channel platinum RTD,to,oltage signal con'itioner0$==J RTD

$ 1 Analog

M%>4 :,thermocouple to,'igital conerter 0=C to H1$#C 1 1 3,&ire

M%>, :,thermocouple to,'igital conerter 0=C to H1=$4C 1 1 3,&ire

M%! Thermistor,to,'igital conerter 1 = 3,&ire

M%' 4,channel thermistor,to,pulse,&i'th conerter 4 = -ulse

M%!7,channel precision temp monitor 03 remote 1 local 3thermistor

1 $,&ire

M%3'!,8Col',Bunction,compensate' 1,&ire thermocouple,to,'igital conerters )or t(pes % O : N an' T

1 1 1,&ire

M%3'!,'Col',Bunction,compensate' 1,&ire thermocouple,to,'igital conerters )or t(pes R an' S

1 1 1,&ire

M%3'!,,Col',Bunction,compensate' 1,&ire thermocouple,to,'igital conerters )or t(pes % O : N R S an' T

1 1 3,&ire

M%3'!, RTD,to,'igital conerter 1 = S-I

"sing Thermal Management Components#$rinciples and%pplication Circuits

Sensing Docation: The 6ey to Choosing the &ight Sensor TypeThe )irst step in using a temperature sensor is to select the right 2in' o) sensor )or theapplication. To egin (ou nee' to un'erstan' the target &hose temperature is to emeasure'. Some common measurement targets are liste' here along &ith recommen'e'sensor t(pes.

Sensing $C ?oard TemperatureSur)ace,mount sensors are i'eal )or -C oar' measurement. RTDs thermistors an' ICsensors are aailale in sur)ace,mount pac2ages an' temperature ranges that are compatile&ith sensing the temperature o) a -C oar'. /ecause o) their inherent linearit( an' lo& costIC sensors are generall( the est choice. ICs hae a''itional )eatures such as 'igital inter)aceor thermostat )unctions. These )eatures usuall( gie them the e'ge in terms o) s(stem cost'esign comple


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to select among seeral slae a''resses. "or e


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thermistor is &ell,separate' )rom the sur)ace o) the oar' an' the length o) the lea's proi'esthermal isolation )rom the oar'.

Temperature sensor ICs in sur)ace,mount pac2ages are more 'i))icult to use )or measuringamient temperature ecause the est thermal path )or an IC sensor is through its lea's&hich are at the same temperature as the -C oar'. I) the -C oar' is at amienttemperature a sensor mounte' on the oar' &ill measure the amient temperature. ?o&eeri) the -C oar' contains components that 'issipate enough po&er to raise its temperatureaoe amient the IC &ill measure the eleate' oar' temperature not the amienttemperature.Some IC pac2ages such as the T!9$ raise the IC sensor aoe the -C oar'. ?o&eerT!9$ pac2ages con'uct heat er( &ell through their lea's &hich can cause the measure'temperature to e strongl( a))ecte' ( the -C oar' temperature. )igure 3 sho&s a

Figure *&. Thermistor monitoring air temperature. "ote that the long thermistor leads providethermal isolation from the boards surface.

temperature sensor IC in a oar',mounte' T!9$. I) the oar' at the temperature sensorFslocation is near amient temperature the sensor can proi'e a goo' in'ication o) airtemperature. I) a heat source such as a po&er component or other 'eice that operates at aneleate' temperature is near the sensor as sho&n in )igure 3a the oar'Fs temperature atthat location &ill e greater than the amient temperature. This &ill in)luence the ICFs 'ietemperature an' cause errors in the amient temperature measurement. Copper et&een hotoar' areas an' the sensor location &ill con'uct heat to the icinit( o) the sensor &hich alsocauses errors. The t&o gui'elines elo& &ill help to 2eep the sensor temperature as close aspossile to the air temperature

Locate the sensor as )ar as possile )rom high,temperature components. I) practical thesensor shoul' e at the coolest part o) the oar'.

%liminate as much copper as possile )rom the icinit( o) the sensor. I) practical theonl( copper near the sensor shoul' e the minimum,&i'th traces necessar( to connectto the sensorFs po&er an' I! pins. ItFs not al&a(s practical ut i) the sensor is the onl(component &ithin a ra'ius o) a )e& cm heat generate' on the oar' &ill hae lesse))ect on the measure' air temperature.

8=


52/89

"ollo&ing the t&o gui'elines aoe can help the sensorFs reporte' temperature to e &ithin a'egree or t&o o) amient 'epen'ing on seeral )actors such as the oar' an' amienttemperatures. !ther techniues such as 'rilling holes aroun' the sensor to minimi+e thermalcon'uction ( the oar' ma( e help)ul as &ell.

I) the techniues aoe canFt e use'G'ue to high component 'ensit( on the oar' )ore


53/89

Sensing Temperature of a C$"< Praphics $rocessor< )$P%< %SIC< $oGer +e2ice<etc. Gith an On-Chip Thermal +iode1

As 'iscusse' in the Remote Digital Temperature Sensors section some componentsespeciall( high,per)ormance ICs such as C-6s ;-6s an' "-;As inclu'e a ipolartransistor )or the purpose o) sensing temperature. This is usuall( a -N- &ith the collectorgroun'e'. The ase an' emitter are the 5'io'e connections. /ecause the thermal,sensingtransistor is on the IC 'ie measurement accurac( is )ar etter than &ith other sensingtechniues an' thermal time constants are uite small. *a


54/89

higher,resolution resistance,measuring IC such as the *AE31#8 RTD,to,'igital conerter ora 1,it ADC is usuall( necessar( to achiee su))icient resolution.

)igure 3! sho&s a t(pical cure o) thermistor channel co'e s. temperature )or the *AE9#&hen use' &ith one o) these integrate' thermistors. Note the lo& aailale resolution thoughthe results (iel'e' are usale.

Figure *5. +A;2265 thermistor channel code vs. temperature when used with a #.*M? 'C integratedthermistor.

&emote +iode Sensor Puidelines

$C ?oard Dayout Puidelines for &emote Sensors

"ollo& these gui'elines )or est results &hen using remote temperature sensors. The DE- isthe ano'e connection an' DEN is the catho'e connection. Note that accurac( &ill 'epen' onthe amount o) noise pic2up the e))ects o) &hich are not easil( pre'ictale. Al&a(s eri)(

accurac( e)ore committing to a )inal la(out.

1. -lace the remote sensor as close as is practical to the thermal 'io'e. In nois( enironmentssuch as a computer motheroar' this 'istance can e up to aout $=cm. This length can eincrease' i) the &orst noise sources are aoi'e'. Noise sources inclu'e CRTs cloc2generators memor( uses an' -CI uses.

$. Do not route the DE-,DEN traces across or in parallel to near( )ast 'igital signals &hichcan easil( intro'uce H3=C error een &ith goo' )iltering.

3. Route the DE- an' DEN traces in parallel an' in close pro


55/89

oltage traces such as H1$@DC. Lea2age currents )rom -C oar' contamination must eminimi+e' a $=*J lea2age path )rom DE- to groun' causes aout H1C error. I) high,oltage traces are unaoi'ale connect guar' traces to ;ND on either si'e o) the DE-,DEN traces 0see )igure 3.

4. Route through as )e& ias an' crossun'ers as possile to minimi+e coppersol'erthermocouple e))ects.

8. 6se &i'e traces &hen practicalG8mil to 1=mil traces are t(pical. /e a&are o) the e))ect o)trace resistance on temperature rea'ings &hen using long narro& traces.

. >hen the po&er suppl( is nois( a'' a resistor 0up to 47J in series &ith @CC.7. -lace a )ilter capacitor across the DE-,DEN inputs locate' near the remote sensor IC. 6se

a alue recommen'e' in the sensorFs 'ata sheet.

Figure *6. Recommended D;-D;" C board traces. The two outer guard traces are recommendedif high-voltage traces will be near the D;" and D; traces.

Ca(le Connections to Thermal +iodes Sometimes thermal 'io'es nee' to e locate' at'istances that e


56/89

)or&ar' current gain 08= \ eta \ 18= )or ee hae osere' ariations in remotetemperature rea'ings o) less than M$C &ith a ariet( o) 'iscrete transistors. Still it is goo''esign practice to eri)( consistenc( o) temperature rea'ings &ith seeral 'iscrete transistors)rom an( manu)acturer un'er consi'eration.

Thermal +iode +esign PuidelinesSome IC en'ors such as those in the usiness o) selling microprocessors an' "-;As haeeen inclu'ing thermal 'io'es in their pro'ucts )or (ears an' hae a goo' un'erstan'ing o)ho& to 'esign these 'eices. "or )irst,time 'esigners o) ICs that &ill incorporate thermal'io'es this section o))ers some instructie gui'elines

1. *inimi+e the internal resistance o) the 'io'e. As note' e)ore aout H=.48C error &illresult )rom each ohm o) series resistance. I) a transistor is use' in a 'io'e,connecte'con)iguration &ith the ase connecte' to the collector the ase resistance can e a )actoro) eta higher. In this case the collector resistance &ill not matter unless it causes the'eice to saturate at 1==A &hen 'io'e,connecte'.

$.

*a


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A. -h(sicall( separate the sense 'eice an' metal carr(ing )ast 'igital signals. Alsoph(sicall( separate 'igital signals )rom the metal et&een the sense transistor an' theon'ing pa's.

/. Do not locate the on'ing pa's )or the sense Bunction ne


58/89

H8@

RCA/L%

4,&ire RTDR

CA/L%

RCA/L%

RCA/L%

RR%"

42

-;A

!6T1

R%"INH

*!D6LAT!R

M%'48

R%"IN,

!6T$

AIN1

AIN$

A;ND

D;ND

@H @DD

$2

Figure 01a. 0-wire interface for a T1## or T1### RTD. �

H8@

3,&ire RTD RCA/L%

RCA/L%

RCA/L%

RR%"

42

-;A

!6T1

R%"INH

*!D6LAT!R

M%'48

R%"IN,

!6T$

AIN1

AIN$

A;ND

D;ND

@H @DD

12

Figure 01b. *-wire interface for a T1## or T1### RTD.

)igure 4'( sho&s the same ADC use' &ith a 3,&ire RTD. The 3,&ire connections help tore'uce the cost si+e an' &eight o) caling ( using a pair o) current sources to 'rie t&o o)the RTDFs lea' &ires. I) the &ire resistances are &ell,matche' eual oltage 'rops &ill ecreate' across the t&o &ires 'rien ( the current sources there( eliminating measurementerrors 'ue to cale resistance.

87


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)igure 4'c sho&s the *AE31#8 RTD 'igiti+er con)igure' to accept $, 3, or 4,&ire RTDsthrough a single terminal loc2. Oumpers on the terminal loc2 select $, an' 3,&ire operation.Note that the *AE31#8 'oes not use current sources )or sensor e


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Figure 0!. T1## linearier circuit. �

Figure 0*. :rror curve showing the deviation from linearit between -1##'C and %!##'C for theoutput of the circuit in Figure 0!.

89


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Thermocouple Interface Circuits

As 'iscusse' in the Thermocouples section a thermocouple inter)ace circuit normall( inclu'esa high,resolution ADC a col',Bunction temperature sensor a oltage re)erence an' aprecision ampli)ier. The circuit sho&n in )igure 44 uses an ADC 0the *E77=8 &ith an internal

programmale gain ampli)ier 0-;A &hich eliminates the nee' )or an e


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)igure 4,a sho&s a )ull( integrate' thermocouple,to,'igital circuit. This circuit measuresthermocouple an' col',Bunction temperature an' a''s the t&o )or )irst,or'er col',Bunctioncompensation. The col',Bunction temperature 'ata is aailale separatel( so that lineari+ationo) the thermocoupleFs trans)er )unction ma( e 'one ( the *C6 i) necessar(. No eire inter)ace also proi'es asimple &a( to net&or2 multiple thermocouples as each unit has a uniue 4,it a''ress.

*AE31#8= ersions are aailale )or % O : N an' T thermocouples &hile *AE31#81ersions are aailale )or R an' S thermocouples.

Figure 0&a.


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Figure 0&b. /loc2 'iagram o) the *AE31#8= an' *AE31#81 1,>ire thermocouple,to,'igital ICs.

I&-DinFed Temperature Sensor

>hen galanic isolation or improe' %*I immunit( is nee'e' an IR lin2 et&een thetemperature sensor an' the s(stem can e an e


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(b

Figure 02. po&ers a *AE87 temperature,to,perio' sensor )rom an RS,$3$inter)ace IC &hich also cone(s the sensorFs output &ae)orm to the s(stem. The *AE87Fsoutput &ae)orm has a perio' that is 'irectl( relate' to temperature. *ore 'etails can e )oun'in *a


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Figure 0/. R3-!*!-powered temperature sensor.

)an Control Circuits

)an Control $artitioning

There are seeral 'i))erent &a(s to implement )an control in a s(stem. The est approach )or agien s(stem 'epen's on the characteristics o) the s(stem the ease 0or 'i))icult( o)'eeloping ne& )an control )irm&are an' other )actors. Some common approaches are'escrie' elo&.

System Microcontroller Managing )an Speed ControlI) the s(stem 'esign alrea'( inclu'es a microcontroller per)orming s(stem management tas2sthat microcontroller ma( also e ale to han'le )an spee' control )unctions. Themicrocontroller nee's to hae enough I!s aailale to monitor TAC? signals an' generate->* spee' control signals. I) the )ans &ill e controlle' using a ar(ing DC suppl( themicrocontroller &ill nee' either DAC outputs to control the output oltages o) the )ansF po&er

supplies or e* signal into a DC po&er,suppl( oltage."irm&are is nee'e' to interpret temperature 'ata an' TAC? signals generate the correct->* &ae)orms &ith appropriate ramp rates proi'e spin,up )unctions an' han'le )aultcon'itions. I) the microcontroller is capale o) per)orming these )unctions )an control can ea''e' to the s(stem &ith little a''itional har'&are cost. "irm&are 'eelopment cost 'epen'son the numer o) )ans an' the sophistication o) the control an' monitoring algorithms. )igure4! sho&s in simpli)ie' )orm ho& this approach can e implemente'.

4


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Figure 05. hen sufficient


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3, or 4,>ire Cooling "ans

To ?ost-

+A;*1/5!

*SDA

*SCL

@DD

@SS 03

SDA

SCL

R S T

AD=N

AD=-

AD1N

AD1-

AD$N

AD$-

AD3N

AD3-

AD4N

AD4-

AD8N

AD8-

TAC?.8

TAC?.4

->*.4

->*.8

-.= TC:

-.1 TDI

-.$ T*S T//

-.3 TD!

-.4 T/A

R%;1#

R%;$8

3.3@

D3/&

I$C TempSensor

;-I! A Special"unctions

TAC?

->*

TAC?

TAC?.=

1$@ 1$@

->*

TAC?.3

TAC?.$

->*.$

->*.3

TAC?

->*

TAC?

1$@ 1$@

->*

TAC?.1

->*.=

->*.1

TAC?

->*

TAC?

1$@ 1$@

->*

I$C -eripheral

%hen a s(stem management microcontroller is capale o) monitoring temperature an''etermining target )an spee's ut 'oes not hae enough I!s or an'&i'th )or controlling an'

monitoring the spee's o) multiple )ansGor i) the time an' cost inole' in 'eelopingintelligent )an control )irm&are are e* an' TAC? signals et&een the )ans an' the microcontroller


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a couple o) I$C inter)ace signals han'le the communication et&een the s(stem *C6 an' the)an inter)ace. The *AE3179= multichannel ->* )an spee' controller is an e


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TEMP

SENSO

controller. The fan speed controller ma or ma not have temperature sensing capabilit. The+A;*1/6# shown here produces si) + signals for individual closed-loop speed control ofup to si) fans.


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The e


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Figure &!b. 3tand-alone speed controller for 0-wire fans or other fans with speed-control inputs.The TACJ or loc$ed-rotor output (if available is not used b the +A;*1/0#.

$ulse-Jidth-Modulated< )an $oGer-Supply +ri2e

As 'iscusse' in the Controlling Fan Speed section this approach is simple an' appropriate&hen the 'ra&ac2s o) increase' noise an' more 'i))icult tachometer sensing are not issues.)igure ,3 sho&s high,si'e an' lo&,si'e ersions that &or2 &ith seeral *a* signal polarit( nee's to e negatie an' the->* output must e ale to pull up to the )anFs suppl( oltage. In )igure ,3(As lo&,si'e 'riecircuit note that the ->* polarit( is positie. The ->* output nee's to e pulle' up onl( highenough to turn on the n,channel "%T. "or oth circuits pulse stretching ma( e nee'e' toensure proper operation o) the tachometer counterGthis is especiall( true )or slo&er )ans.

7=


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Figure &*. *-wire fan control circuits using pulse-width modulation of the fans power suppl. !-wirefans can be controlled with the same circuits, but do not have tachometer outputs. (a Jigh-sidedrive. (b =ow-side drive.

4-Jire )an +ri2e

The 4,&ire )ans normall( reuire a high,)reuenc( 0$=2?+ to 8=2?+ ->* signal )or )ancontrol. The circuit in )igure ,4 sho&s the *AE39 'ual )an spee' controller use' &ith t&o4,&ire )ans. The *AE39 also inclu'es t&o temperature,sensing channels an' is capale o)controlling )an R-* as a )unction o) measure' temperature. /e sure to chec2 the 'ata sheet o)an( 4,&ire )an un'er consi'eration the recommen'e' ->* )reuenc( is not al&a(s greater

than $=2?+. *an( )an controller ICs hae seeral aailale output )reuencies toaccommo'ate such )ans.

71


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Figure &0. The +A;22*6 controlling two 0-wire fansO it measures two temperatures and can controlfan R+ based on the measured temperature.

Con2erting $JM Control Signals to Dinear )an +ri2e

*ost )an control ICs generate ->* signals to control )an spee'. These signals are

appropriate )or 4,&ire )ans an' &hen use' to mo'ulate the po&er suppl( can o)ten e use'&ith $, an' 3,&ire )ans as &ell. >hen a pulse,&i'th,mo'ulate' po&er suppl( is not acceptale(ou must 'rie a $, or 3,&ire )an &ith a linear oltage to a'Bust spee'. I) the )an controllergenerates ->* )or )an spee' control one o) the )ollo&ing circuits can e use' to conert the->* signal to a linear oltage.

+iscrete $JM-to-Dinear )an +ri2eThe circuit in )igure ,, is appropriate )or use &ith most ->* )an control ICs. It )ilters the->* signal an' ampli)ies an' u))ers the resulting DC oltage to 'rie the )an. The $.$"capacitor is necessar( )or )iltering lo&,)reuenc( 01==?+ ->* &ae)orms. Spee' controllersli2e the *AE39 hae higher )reuenc( ->* 0aoe $=2?+ &hich allo&s the $.$"

capacitor to e replace' &ith a smaller alue. It is goo' practice to use the highest ->*)reuenc( aailale. The circuit sho&n &ill &or2 &ith all o) *a*,output )ancontrollers inclu'ing the *AE18 *AE1 *AE39 *AE4= *AE317#8 an'*AE3179=.

Note that using linear pass transistors as in "igure 88 &ill result in some &aste' po&er. >henthe )anFs po&er,suppl( oltage is hal) o) the nominal suppl( oltage the pass 'eice &ill'issipate appro


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&ill &or2 &ith most ->*,output )an controllers. In general the highest aailale )an controller->* )reuenc( shoul' e use'.

Figure &&. Circuit for converting + fan control signals to a linear suppl voltage. �

Figure &2. =inear drive from a +-output fan controller using an e)ternal switch-mode voltageregulator.

73


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Dinear )an +ri2e

A )e& *a


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4!< 4-Jire )an Speed Control

The 4,&ire )ans are eas( to a'apt to high,oltage operation ecause the )an controller is note


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Figure &6. Controlling a 05 !- or *-wire fan b modulating the power suppl with a + signal.

4!< Dinear )an Speed Controller

The *AE8= an' *AE81 are )an R-* controllers 'esigne' )or use &ith 1$@ )ans. In thestan'ar' con)iguration an n,channel "%T 'ries the lo& si'e o) the )an an' the tachometersignal )rom the )an 'ries the ICFs TAC? input0s. @oltage )ee'ac2 is ta2en )rom the "%TFs'rain 0the )anFs groun' terminal.

>hen a 4#@ )an is use' &ith the *AE8= or *AE81 a "%T &ith a higher oltage ratingmust e selecte' an' the oltage )ee'ac2 )rom the 'rain an' the tachometer signal )rom the)an must e attenuate' so that the( 'o not e


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Figure 2#. 05, linear fan R+ controller. The feedbac$ and tachometer signals are attenuated forcompatibilit with the +A;22&1s input voltage tolerance.

On5Off )an Control Circuits>hile )an control ase' on programmale ICs an' microcontrollers proi'es e


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Figure 21. =ocal on?off fan controllers with factor-set thresholds. (a ses a temperature switch anda F:T to enable the fans power suppl for !- and *-wire fans. (b The temperature switchs outputdirectl drives a 0-wire fans + input to activate the fan.

Docal Sensing< %dQusta(le Threshold

The circuits in )igure are similar to those in "igure 1 e


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Figure 2!. =ocal on?off fan controllers with ad7ustable thresholds. (a sing a temperature switchand a F:T to enable the fans power suppl for !- and *-wire fans. (b The temperature switchsoutput directl drives a 0-wire fans + input to activate the fan. The e)ternal resistor sets the tripthreshold.

&emote Sensing< )actory-Set ThresholdThe )an ono)) controllers in the t&o preious )igures use local temperature s&itches so the(ma2e the 'ecision to actiate the )an ase' on oar' temperature. >hen the 'ecision nee'sto e ma'e ase' on either air temperature or the temperature o) an IC through a thermal'io'e a remote temperature s&itch is a etter choice. The circuits in )igure 3 are similar tothose in "igures 1 an' $ ut use a remote,sensing temperature s&itch to 'etermine&hether the temperature has e* input o) a4,&ire )an actiating the )an &hen the air temperature e


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Figure 2*. Remote, on?off fan controllers with factor-set thresholds. (a ses a remote temperatureswitch and a F:T to enable the fans power suppl for !- and *-wire fans. (b The temperatureswitchs output directl drives a 0-wire fans + input to activate the fan.

Simple< TGo-Speed )an Controller

Some s(stems normall( operate at a temperature high enough that the )an must e spinningut lo& enough that it can sa)el( operate at a lo& spee'. In these cases a t&o,spee' 0lo& an'high )an controller is a goo' solution. The circuit in )igure 4 is an e


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Figure 20. Remote, two-speed fan controller with factor-set threshold. 9elow the threshold, the fanruns at appro)imatel half speed. Above the threshold, it runs at full speed.

In "igure 4 the *AE#Fs open,'rain n,channel "%T is o)) at temperatures elo& thethreshol'. >hile the "%T is o)) the pnp 'ries the groun' lea' o) the )an. >ith the pnpFs ase

connecte' to H8@ the oltage across the )an is a little oer @ enough to ensure lo&,spee'operation )or most small )ans. /e sure to eri)( operation o) (our )an &ith a @ po&er suppl(e)ore using this circuit. >hen the threshol' is e


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Temperature SGitches

In-Circuit Temperature SGitch Testing

>hen a temperature s&itch is use' )or s(stem protection the trip temperature is normall( setto a alue &ell aoe the operating range o) the s(stem. So ho& 'o (ou eri)( at the oar'

leel that a temperature s&itch &ith a )i'oes this &ith t&o temperature s&itches that monitor t&o separate hot spots. I) onl( one hotspot is to e monitore' one o) the temperature s&itches an' the !R gate can e eliminate'. Ahigh,temperature con'ition turns on the silicon,controlle' recti)ier 0SCR &hich shorts thepo&er suppl( an' lo&s the )use.

#$


84/89

Figure 2/. 8vertemperature crowbar circuit with two temperature switches.


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%dditional &esources

%pplication *otes< Tutorials< and &eference +esigns

Seeral application notes tutorials an' re)erence 'esigns relate' to temperature sensing an')an control can e )oun' on the *a $! T!%( S!#*o"

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)8/:

o S%*s %* t is2ate a 5A69/:9 te'erat3re-t-'eri sensr 3sing an IR 2in?.

AN32: RS.232.Po!"! T!%(!"+'"! S!#*o"

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)88

o

S%*s a "ir"3it !r '*ering an "3ni"a4ng *it% a 5A69/:: te'erat3re-t-!re3en"@ sensr *it% RS-.

AN105=: Co%(!#*+/#- >o" I!+),4 F+&o" +# S!",!* R!*,*+#&! D,?!"!#&!* !!!# T$!"%+).S!#*! D,o!*

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)10/:

o Dis"3sses te'erat3re eas3reent ee"ts ! 3sing ies *it% ierent iea2it@ !a"trs.

AN3502: E?!& o> PC Bo+" T"+&! W,$ o# R!%o!.D,o! T!%(!"+'"!.S!#*o" A&&'"+&4

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)/0

o Dis"3sses e,terna2-ie te'erat3re eas3reent errrs 3e t 2ng =C 7ar tra"es.

#4


86/89

AN206: C'"7!.F,@#- $! E""o" o> + B+#-+(.B+*! D,-,+) T!%(!"+'"! S!#*o"

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)0>

o Des"ri7es a te"%ni3e !r errr-"rre"4ng 7anga' te'erat3re sensrs 3sing "a2i7ra4n ata.

AN362: O7!"7,! o> ,B'o# S!#*o"* +# T!%(!"+'"!H'%,,4 D++ Lo--!"*

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)>

o =ries an intr3"4n t 5a,is iB3&n te'erat3re an %3iit@ nitrs.

REFD5150: S,%()! W,"!)!** T!%(!"+'"! Mo#,o" A)*o H+* D++.Lo--,#- C+(+,),/!*

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)/1/0

o In"23es esigns !r a -"%i' transi&er an a -"%i' re"eier "ir"3it 7ase n t%e 5A69/:: !re3en"@-3t'3t

te'erat3re sensr.

AN3316: HFAN.0620: Ho o Co#"o) +# Co%(!#*+! + T$!"%o!)!&",& Coo)!" TEC

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)1>

o Des"ri7es t%e esign ! a "ntr2 2' !r a TEC.

AN1=6: F+# S(!! Co#"o) ,* Coo)

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)1:>8

o

Dis"3sses !3naenta2s ! !an s'ee "ntr2 an s%*s e,a'2e "ir"3its 3sing t%e 5A699/0 an 5A699/1

2inear !an s'ee "ntr22ers.

AN60: R!7 U( Yo'" F+#.S(!! Co#"o) D!*,-#*

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)>0

o Dis"3sses !an s'ee "ntr2 7asi"s an s%*s "ir"3its 3sing t%e 5A699/0 an 5A699/1 2inear !an s'ee

"ntr22ers !r "ntr22ing %ig%-2tage !ans. Is2ate "ir"3its are a2s s%*n.

AN50: G!@#- S+"! ,$ $! MAX51 F+# Co#"o))!"

o %&'())***.a,iintegrate.")a''-ntes)ine,.')i)88/0

o =ries r*are e,a'2es !r t%e 5A699/1 2inear !an s'ee "ntr22er.

"in' current in)ormation aout all o) *a


87/89

S'& is a trademar% o! $otorola( &nc.

)*ire is a registered trademar% o! $a+im &ntegrated 'roducts( &nc.

#


88/89

Amient Air Sensing 49 81 Analog Temperature Sensor 13 14

Cur,e 18 -onlinearit 18

Callen'ar,@an Dusen euation 7 Digital Temperature Sensor

"eatures 1#

Local $= Remote $1 $#

"an $,>ire 3$ 3,>ire 33 4,>ire 33

"an Spee' *onitoring 37 41

"an Spee' Control 31 34 44 4,&ire )an 71

Acoustic noise 37

Close',loop R-* 41 Controller "unctions 3$ "ailsa)e circuit #1 ?igh,oltage 4,&ire 78 7 ?igh,oltage linear 7 Linear po&er suppl( 38 !n!)) 77 7# 79 ->* po&er suppl( 3 ->*,to,linear conersion 7$ R-* control 41

Two-speed #1

&C Die Temperature Sensing

Thermal diode $1 $3 8$ Thermistor 83

I'ealit( "actor 14 $4 $8 $7 8$ 88 Nonlinearit(

NTC thermistor 4 8 RTD 7 # 8# Thermocouple 1=

NTC 4 44 Cur,e 8

Nonlinearit( 4

-rinte' Circuit /oar' Sensing 4# 49 -t1== 7 # 8 87 8# 89

Linearit Correction 89 Remote Dio'e Sensor $1 $# 8$

Cale connection 84 Dio'e 'esign gui'elines 8 Discrete 'io'e 88 %rror sources $3

"eatures $ La(out gui'elines 84

R-* Control 41 RTD 7 # 9 14 44 4# 49 8 8#

Alpha 7 Callen'ar,@an Dusen euation 7 Cur,e #

Linearit Correction 89 Nonlinearit( 7 # 8# -t1== 7 # 8 87 8# 89 Signal con'itioner 9 Temperature range 7

SA*A 7 Signal Con'itioner

RTD 9 48 8# Thermocouple 4 4# 1

Temperature Sensor

Analog 13

Digital 1 $= IR,lin2e' $ Remote 'igital 13 $1 $# 8$ Remote 'io'e 13 $1 $# 8$ RS$3$,po&ere' 3 RTD 7 Thermistor 4 Thermocouple 11

Temperature S&itch $# $9 7# 79 #= #$ "an spee' control 77 7# 79 #= #1

In,circuit testing #$

Thermal Cro&ar #$ Thermal *anagement

Caliration 3 Control 3 -rotection 3 -urposes 3

Thermistor 4 14 44 4# 49 81 8$ 83 Cur,e 8 Nonlinearit( 4 NTC 4 8 44

Thermocouple 9 1= 11 1$ 13 14 44 4

49 84 = 1 Col' Bunction 1$ Cur,e 11 *AE74 13 *AE78 13 Nonlinearit( 1= Signal con'itioner 1$ Temperature range 9

#7


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T(pe : 1= 11 13

thermal manegement electronic

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