Low-Power TEC Driver - Texas Instruments

1 VINTPS63020 TECVCTRLA pplicationReportSLVA677 December2014 Low-PowerTECD riverJuergenNeuhaeuslerABSTRACTA ttainingthe bestperformancefromelectroniccircuitsmay requireto tightcontrolof the operatingtemperatureof the circuitsor at leastthe temperatureof the keepthetemperaturecloseto the if the ambienttemperatureis not properlycontrolledorcomponentsof the circuitgenerateheatduringoperation(which cannotbe easilypredictedas accurateasneeded),activecontrolof the temperaturemay be (TECs)may help to solvethis usedfor activecoolingandheatingof the controlthe temperatureof the componentswitha TEC,thecurrentflowingthroughit mustbe the directionof the currentflow they are eithercoolingor heatingthe powersupplysolutionwhichcan sourceandsink applicationnotedetailsa circuitimplementationbasedon TI's singleinductorbuck-boostconvertertechnol ogywhichoffersa simplepossiblesolutionfor sucha the examplethe powersupplysolutionis implementedbasedon the completecircuitisshownin CircuitSchematicThe objectiveof this circuitis to controlthe currentflowingthroughthe TECin examplefor a circuitimplementationcan be foundin the TI December2014 Low-PowerTECD riverSubmitDocumentationFeedbackCopyrigh t 2014,TexasInstrumentsIncorporated()

2 1 323max1min13 FBOUTCTRLFBVR RRR VR VVRR = - - +maxmin31maxminCTRLCTRLOUTOUTVVRRVV -= - minminTECOUTINVVV=-maxmaxTECOUTINVVV= shownin Figure1, the circuitconsistsof a buck-boostconverterdesignbasedon the TPS63020almostin its TPS63020is suppliedby a regulatedvoltagerail of V. The TECis connectedbetweenthe outputof the TPS63020basedDCDC converterand its inputsupplyvoltagerailof the TPS63020datasheet(SLVS916), its outputvoltagecan be V and Usingthis voltagerangeat the outputof the buck-boostconverterallowsthe voltageto vary acrosstheTECbetweenVTEC maxof V andVTEC minof Equation1 and Equation2 to calculatethosevalues.(1)(2)In theseequations,VIN, is the regulatedsupplyvoltageof the buck-boostconverter,VOUT maxis themaximum,andVOUT minis the minimumoutputvoltageof the outputvoltageof the buck-boostconverteris programmedwith the feedbackdividerconsistingofR1andR2.

3 To be able to vary the outputvoltage,an additionalresistorR3in the feedbackdividerisconnectedto enablefeedingcurrentinto the feedbackvoltageVFBis regulatedto aconstantvalueof V (TPS63020datasheet,SLVS916), so the controlvoltageVCTRL definesthis calculatean appropriatevaluefor the resistanceofR3, use Equation3.(3)In Equation3,VCTRL maxis the maximumlevelof the controlvoltageandVCTRL minis the minimumvalueof givenresistancevalueforR1of 1 M , and the voltagesforVCTRLmax( V) andVCTRLmin(0 V) theresistanceforR3is calculatedto be 763 k .FinallyR2is calculatedusingEquation4:(4)Withthe valuesfor the parameterspreviouslyused,the resistanceofR2is calculatedas 130 k .To drivethe TECproperly,the buck-boostconvertermustsourceand sink ,this is achievedby forcingthe converterin is doneby disablingthe TPS63020can sourcemorecurrentthanit can sink,it isimportanthow the TECis connectedto the general,the deviceswhichshouldbe kept at this reason, in mostcases,the TECis best connectedin a way that it is coolingthe devicewhiletheTPS63020is December2014 SubmitDocumentationFeedbackCopyright 2014,TexasInstrumentsIncorporatedControl Voltage VCTRL (V)TEC Current (A) = 1 :RTEC = 2 :RTEC = 3 showsthe currentflowingthroughthe TECdependingon the predictedasymmetryof the maximumcurrentsfor sourcingand sinkingare TECC urrentvs.

4 ControlVoltageThis powersupplysolutioncan be usedas powerplantin a controlsystemto controlthe temperatureofthe example,ifVCTRLis generatedby a PWMsignalon a GPIOof a microcontrollerwhichisrunninga temperaturecontrolalgorithm,a closedloop systemis built to controlthe temperatureof thecomponentsattachedto the December2014 Low-PowerTECD riverSubmitDocumentationFeedbackCopyrigh t 2014,TexasInstrumentsIncorporatedIMPORTA NTNOTICET exasInstrumentsIncorporatedand its subsidiaries(TI) reservethe rightto makecorrections,enhancements,improvement sand otherchangesto its semiconductorproductsand servicesper JESD46,latestissue,and to discontinueany productor serviceper JESD48, latestrelevantinformationbeforeplacingor dersand shouldverifythat suchinformationis semiconductorproducts(alsoreferredto hereinas components ) are sold subjectto TI s termsand conditionsof salesuppliedat the time of warrantsperformanceof its componentsto the specificationsapplicableat the time of sale,in accordancewith the warrantyin TI s termsand conditionsof sale of otherqualitycontroltechniquesare usedto the extentTI deemsnecessaryto supportthis applicablelaw, testingof all parametersof eachcomponentis not assumesno liabilityfor applicationsassistanceor the designof Buyers responsiblefor theirproductsandapplicationsusingTI minimizethe risksassociatedwith Buyers productsand applications,Buyersshouldprovideadequate designand doesnot warrantor representthat any license,eitherexpressor implied,is grantedunderany patentright,copyright,maskworkright,orot herintellectualpropertyrightrelatingto any combination,machine.

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