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LM202.
4V,10A,SC70,microSMDTemperatureSensorGeneralDescriptionTheLM20isaprecisionanalogoutputCMOSintegrated-circuittemperaturesensorthatoperatesovera55Cto+130Ctemperaturerange.
Thepowersupplyop-eratingrangeis+2.
4Vto+5.
5V.
ThetransferfunctionofLM20ispredominatelylinear,yethasaslightpredictableparaboliccurvature.
TheaccuracyoftheLM20whenspeci-fiedtoaparabolictransferfunctionis±1.
5Catanambienttemperatureof+30C.
Thetemperatureerrorincreaseslin-earlyandreachesamaximumof±2.
5Catthetemperaturerangeextremes.
Thetemperaturerangeisaffectedbythepowersupplyvoltage.
Atapowersupplyvoltageof2.
7Vto5.
5Vthetemperaturerangeextremesare+130Cand55C.
Decreasingthepowersupplyvoltageto2.
4Vchangesthenegativeextremeto30C,whilethepositiveremainsat+130C.
TheLM20'squiescentcurrentislessthan10A.
Therefore,self-heatingislessthan0.
02Cinstillair.
Shutdowncapa-bilityfortheLM20isintrinsicbecauseitsinherentlowpowerconsumptionallowsittobepowereddirectlyfromtheoutputofmanylogicgatesordoesnotnecessitateshutdownatall.
ApplicationsnCellularPhonesnComputersnPowerSupplyModulesnBatteryManagementnFAXMachinesnPrintersnHVACnDiskDrivesnAppliancesFeaturesnRatedforfull55Cto+130CrangenAvailableinanSC70andamicroSMDpackagenPredictablecurvatureerrornSuitableforremoteapplicationsKeySpecificationsjAccuracyat+30C±1.
5to±4C(max)jAccuracyat+130C&55C±2.
5to±5C(max)jPowerSupplyVoltageRange+2.
4Vto+5.
5VjCurrentDrain10A(max)jNonlinearity±0.
4%(typ)jOutputImpedance160(max)jLoadRegulation0AV+),thecurrentatthatpinshouldbelimitedto5mA.
Note3:Thehumanbodymodelisa100pFcapacitordischargedthrougha1.
5kresistorintoeachpin.
Themachinemodelisa200pFcapacitordischargeddirectlyintoeachpin.
Note4:SeeAN-450"SurfaceMountingMethodsandTheirEffectonProductReliability"orthesectiontitled"SurfaceMount"foundinanypost1986NationalSemiconductorLinearDataBookforothermethodsofsolderingsurfacemountdevices.
Note5:Thejunctiontoambientthermalresistance(θJA)isspecifiedwithoutaheatsinkinstillairusingtheprintedcircuitboardlayoutshowninFigure1.
Note6:TypicalsareatTJ=TA=25Candrepresentmostlikelyparametricnorm.
Note7:LimitsareguaranteedtoNational'sAOQL(AverageOutgoingQualityLevel).
Note8:Accuracyisdefinedastheerrorbetweenthemeasuredandcalculatedoutputvoltageatthespecifiedconditionsofvoltage,current,andtemperature(expressedinC).
Note9:Non-Linearityisdefinedasthedeviationofthecalculatedoutput-voltage-versus-temperaturecurvefromthebest-fitstraightline,overthetemperaturerangespecified.
Note10:Regulationismeasuredatconstantjunctiontemperature,usingpulsetestingwithalowdutycycle.
Changesinoutputduetoheatingeffectscanbecomputedbymultiplyingtheinternaldissipationbythethermalresistance.
Note11:NegativecurrentsareflowingintotheLM20.
PositivecurrentsareflowingoutoftheLM20.
UsingthisconventiontheLM20canatmostsink1Aandsource+16A.
Note12:Loadregulationoroutputimpedancespecificationsapplyoverthesupplyvoltagerangeof+2.
4Vto+5.
5V.
Note13:Lineregulationiscalculatedbysubtractingtheoutputvoltageatthehighestsupplyinputvoltagefromtheoutputvoltageatthelowestsupplyinputvoltage.
TypicalPerformanceCharacteristicsPCBLayoutsUsedforThermalMeasurementsTemperatureErrorvsTemperatureDS100908-25DS100908-29a)Layoutusedfornoheatsinkmeasurements.
DS100908-30b)Layoutusedformeasurementswithsmallheathink.
FIGURE1.
PCBLyoutsusedforthermalmeasurements.
LM20www.
national.
com41.
0LM20TransferFunctionTheLM20'stransferfunctioncanbedescribedindifferentwayswithvaryinglevelsofprecision.
Asimplelineartransferfunction,withgoodaccuracynear25C,isVO=11.
69mV/CxT+1.
8663VOverthefulloperatingtemperaturerangeof55Cto+130C,bestaccuracycanbeobtainedbyusingthepara-bolictransferfunctionVO=(3.
88x106xT2)+(1.
15x102xT)+1.
8639solvingforT:Alineartransferfunctioncanbeusedoveralimitedtempera-turerangebycalculatingaslopeandoffsetthatgivebestresultsoverthatrange.
AlineartransferfunctioncanbecalculatedfromtheparabolictransferfunctionoftheLM20.
Theslopeofthelineartransferfunctioncanbecalculatedusingthefollowingequation:m=7.
76x106xT0.
0115,whereTisthemiddleofthetemperaturerangeofinterestandmisinV/C.
ForexampleforthetemperaturerangeofTmin=30toTmax=+100C:T=35Candm=11.
77mV/CTheoffsetofthelineartransferfunctioncanbecalculatedusingthefollowingequation:b=(VOP(Tmax)+VOP(T)+mx(Tmax+T))/2,where:VOP(Tmax)isthecalculatedoutputvoltageatTmaxusingtheparabolictransferfunctionforVOVOP(T)isthecalculatedoutputvoltageatTusingtheparabolictransferfunctionforVO.
UsingthisprocedurethebestfitlineartransferfunctionformanypopulartemperaturerangeswascalculatedinFigure2.
AsshowninFigure2theerrorthatisintroducedbythelineartransferfunctionincreaseswithwidertemperatureranges.
2.
0MountingTheLM20canbeappliedeasilyinthesamewayasotherintegrated-circuittemperaturesensors.
Itcanbegluedorcementedtoasurface.
ThetemperaturethattheLM20issensingwillbewithinabout+0.
02Cofthesurfacetempera-turetowhichtheLM20'sleadsareattachedto.
Thispresumesthattheambientairtemperatureisalmostthesameasthesurfacetemperature;iftheairtemperatureweremuchhigherorlowerthanthesurfacetemperature,theactualtemperaturemeasuredwouldbeatanintermediatetemperaturebetweenthesurfacetemperatureandtheairtemperature.
ToensuregoodthermalconductivitythebacksideoftheLM20dieisdirectlyattachedtothepin2GNDpin.
ThetemperturesofthelandsandtracestotheotherleadsoftheLM20willalsoaffectthetemperaturethatisbeingsensed.
Alternatively,theLM20canbemountedinsideasealed-endmetaltube,andcanthenbedippedintoabathorscrewedintoathreadedholeinatank.
AswithanyIC,theLM20andaccompanyingwiringandcircuitsmustbekeptinsulatedanddry,toavoidleakageandcorrosion.
Thisisespeciallytrueifthecircuitmayoperateatcoldtemperatureswhereconden-sationcanoccur.
Printed-circuitcoatingsandvarnishessuchasHumisealandepoxypaintsordipsareoftenusedtoensurethatmoisturecannotcorrodetheLM20oritsconnec-tions.
Thethermalresistancejunctiontoambient(θJA)isthepa-rameterusedtocalculatetheriseofadevicejunctiontem-peratureduetoitspowerdissipation.
FortheLM20theequationusedtocalculatetheriseinthedietemperatureisasfollows:TJ=TA+θJA[(V+IQ)+(V+VO)IL]whereIQisthequiescentcurrentandIListheloadcurrentontheoutput.
SincetheLM20'sjunctiontemperatureistheactualtemperaturebeingmeasuredcareshouldbetakentominimizetheloadcurrentthattheLM20isrequiredtodrive.
ThetablesshowninFigure3summarizetheriseindietemperatureoftheLM20withoutanyloading,andthether-malresistancefordifferentconditions.
TemperatureRangeLinearEquationVO=MaximumDeviationofLinearEquationfromParabolicEquation(C)Tmin(C)Tmax(C)55+13011.
79mV/CxT+1.
8528V±1.
4140+11011.
77mV/CxT+1.
8577V±0.
9330+10011.
77mV/CxT+1.
8605V±0.
70-40+8511.
67mV/CxT+1.
8583V±0.
6510+6511.
71mV/CxT+1.
8641V±0.
23+35+4511.
81mV/CxT+1.
8701V±0.
004+20+3011.
69mV/CxT+1.
8663V±0.
004FIGURE2.
Firstorderequationsoptimizedfordifferenttemperatureranges.
LM20www.
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com52.
0Mounting(Continued)3.
0CapacitiveLoadsTheLM20handlescapacitiveloadingwell.
Withoutanypre-cautions,theLM20candriveanycapacitiveloadlessthan300pFasshowninFigure4.
OverthespecifiedtemperaturerangetheLM20hasamaximumoutputimpedanceof160.
Inanextremelynoisyenvironmentitmaybenecessarytoaddsomefilteringtominimizenoisepickup.
Itisrecom-mendedthat0.
1FbeaddedfromV+toGNDtobypassthepowersupplyvoltage,asshowninFigure5.
InanoisyenvironmentitmayevenbenecessarytoaddacapacitorfromtheoutputtogroundwithaseriesresistorasshowninFigure5.
A1Foutputcapacitorwiththe160maximumoutputimpedanceanda200seriesresistorwillforma442Hzlowpassfilter.
SincethethermaltimeconstantoftheLM20ismuchslower,theoverallresponsetimeoftheLM20willnotbesignificantlyaffected.
4.
0LM20microSMDLightSensitivityExposingtheLM20microSMDpackagetobrightsunlightmaycausetheoutputreadingoftheLM20todropby1.
5V.
Inanormalofficeenvironmentoffluorescentlightingtheoutputvoltageisminimallyaffected(lessthanamillivoltdrop).
IneithercaseitisrecommendedthattheLM20microSMDbeplacedinsideanenclosureofsometypethatminimizesitslightexposure.
Mostchassisprovidemorethanamplepro-tection.
TheLM20doesnotsustainpermanentdamagefromlightexposure.
RemovingthelightsourcewillcauseLM20'soutputvoltagetorecovertothepropervalue.
SC70-5SC70-5noheatsinksmallheatsinkθJATJTAθJATJTA(C/W)(C)(C/W)(C)Stillair4120.
23500.
19Movingair3120.
172660.
15SeeFigure1forPCBlayoutsamples.
microSMDmicroSMDnoheatsinksmallheatfinθJATJTAθJATJTA(C/W)(C)(C/W)(C)Stillair3400.
18TBDTBDMovingairTBDTBDTBDTBDFIGURE3.
TemperatureRiseofLM20DuetoSelf-HeatingandThermalResistance(θJA)DS100908-15FIGURE4.
LM20NoDecouplingRequiredforCapacitiveLoadsLessthan300pF.
R()C(F)20014700.
16800.
011k0.
001DS100908-16DS100908-33FIGURE5.
LM20withFilterforNoisyEnvironmentandCapacitiveLoadinggreaterthan300pF.
Eitherplacementofresistorasshownaboveisjustaseffective.
LM20www.
national.
com65.
0ApplicationsCircuitsDS100908-18FIGURE6.
CentigradeThermostatDS100908-19FIGURE7.
ConservingPowerDissipationwithShutdownDS100908-28MostCMOSADCsfoundinASICshaveasampleddatacomparatorinputstructurethatisnotoriousforcausinggrieftoanalogoutputdevicessuchastheLM20andmanyopamps.
ThecauseofthisgriefistherequirementofinstantaneouschargeoftheinputsamplingcapacitorintheADC.
Thisrequirementiseasilyaccommodatedbytheadditionofacapacitor.
SincenotallADCshaveidenticalinputstages,thechargerequirementswillvarynecessitatingadifferentvalueofcompensatingcapacitor.
ThisADCisshownasanexampleonly.
IfadigitaloutputtemperatureisrequiredpleaserefertodevicessuchastheLM74.
FIGURE8.
SuggestedConnectiontoaSamplingAnalogtoDigitalConverterInputStageLM20www.
national.
com7PhysicalDimensionsinches(millimeters)unlessotherwisenoted5-LeadSC70MoldedPackageOrderNumberLM20BIM7orLM20CIM7XNSPackageNumberMAA05ALM20www.
national.
com8PhysicalDimensionsinches(millimeters)unlessotherwisenoted(Continued)LIFESUPPORTPOLICYNATIONAL'SPRODUCTSARENOTAUTHORIZEDFORUSEASCRITICALCOMPONENTSINLIFESUPPORTDEVICESORSYSTEMSWITHOUTTHEEXPRESSWRITTENAPPROVALOFTHEPRESIDENTANDGENERALCOUNSELOFNATIONALSEMICONDUCTORCORPORATION.
Asusedherein:1.
Lifesupportdevicesorsystemsaredevicesorsystemswhich,(a)areintendedforsurgicalimplantintothebody,or(b)supportorsustainlife,andwhosefailuretoperformwhenproperlyusedinaccordancewithinstructionsforuseprovidedinthelabeling,canbereasonablyexpectedtoresultinasignificantinjurytotheuser.
2.
Acriticalcomponentisanycomponentofalifesupportdeviceorsystemwhosefailuretoperformcanbereasonablyexpectedtocausethefailureofthelifesupportdeviceorsystem,ortoaffectitssafetyoreffectiveness.
NationalSemiconductorCorporationAmericasTel:1-800-272-9959Fax:1-800-737-7018Email:support@nsc.
comNationalSemiconductorEuropeFax:+49(0)180-5308586Email:europe.
support@nsc.
comDeutschTel:+49(0)6995086208EnglishTel:+44(0)8702402171FranaisTel:+33(0)141918790NationalSemiconductorAsiaPacificCustomerResponseGroupTel:65-2544466Fax:65-2504466Email:ap.
support@nsc.
comNationalSemiconductorJapanLtd.
Tel:81-3-5639-7560Fax:81-3-5639-7507www.
national.
com4-BumpmicroSMDBallGridArrayPackageOrderNumberLM20SIBPorLM20SIBPXNSPackageNumberBPA04DDCThefollowingdimensionsapplytotheBPA04DDCpackageshownabove:X1=X2=853m±30m,X3=900m±50mLM202.
4V,10A,SC70,microSMDTemperatureSensorNationaldoesnotassumeanyresponsibilityforuseofanycircuitrydescribed,nocircuitpatentlicensesareimpliedandNationalreservestherightatanytimewithoutnoticetochangesaidcircuitryandspecifications.
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