查詢樣品 說3.5V至60V輸入電壓范 TPS92510是一款配有集成型高側(cè)MOSFET集成型200m?高側(cè)金屬氧化物半導(dǎo)體場效應(yīng)晶體 60V，1.5A峰值電流模式降壓轉(zhuǎn)換器。它被專門設(shè)計管(MOSFET) 成用一個恒定電流驅(qū)動高亮度LED。緊密度容200mV內(nèi)部電壓基 限，200mV內(nèi)部基準(zhǔn)電壓減少了電流感測電阻器中±3%LED電流精 功率耗散。一個的脈寬調(diào)制輸入引腳可實現(xiàn)對100kHz至2.5MHz開關(guān)頻率范 )亮度調(diào)節(jié)輸 TPS92510集成了一個溫度折返特性，此特性能夠LED溫度折 少平均輸出電流來保證感測到的LED溫 簡化對電磁干擾(EMI)的濾除。可調(diào)輸入電壓微型小外形尺寸封裝(MSOP)-10 PowerPAD應(yīng)用范 采用一個10引腳MSOPPowerPAD?封裝MR16LED簡化的 TUDGPleasebeawarethatanimportantnoticeconcerningavailability,standardwarranty,anduseincriticalapplicationsofTexasInstrumentssemiconductorproductsanddierstheretoappearsattheendofthisdatasheet.Copyright?2012,TexasInstrumentsCopyright?2012,TexasInstrumentsPRODUCTIONDATAinformationiscurrentasofpublicationdate.ProductsconformtospecificationsperthetermsoftheInstrumentsstandardwarranty.Productionprocessingdoes EnglishDataSheet:necessarilyincludetestingofallThisintegratedcircuitcanbedamagedbyESD.TexasInstruments mendsthatallintegratedcircuitsbehandledwithappropriateprecautions.Failuretoobserveproperhandlingandinstallationprocedurescancausedamage.ESDdamagecanrangefromsubtleperformancedegradationtocompletedevicefailure.Precisionintegratedcircuitsmaybemoresusceptibletodamagebecauseverysmallparametricchangescouldcausethedevicenottomeetitspublishedspecifications.ORDERINGOUTPUTMINIMUM–40°CtoPowerPADsticTapeand(1)ForthemostcurrentpackageandorderinginformationseethePackageOptionAddendumattheendofthis,orseetheTIwebsiteat UMOveroperatingtemperaturerange(unlessotherwiseInputVPDIM,6SE,3OutputBOOT-8VPH,10-nsVoltagePADtoSourceASinkACOMP,VSENSE,ElectrostaticDischarge(HBM)QSS009-105(JESD22-2ElectrostaticDischarge(CDM)QSS009-147(JESD22-VOperatingjunctiontemperature,Storagetemperature,Stressesbeyondthoselistedunderabsoluteumratingsmaycausepermanentdamagetothedevice.Thesearestressratingsonlyandfunctionaloperationofthedeviceattheseoranyotherconditionsbeyondthoseindicatedunder mendedoperatingconditionsisnotimplied.Exposuretoabsolute-um-ratedconditionsforextendedperiodsmayaffectdevicereliability.THERMALTHERMAL10Junction-to-ambientthermalJunction-to-case(top)thermalJunction-to-boardthermalJunction-to-case(bottom)thermal有關(guān)傳統(tǒng)和全新熱度量的信息，請參閱IC封裝熱度量應(yīng)用報告（文獻(xiàn)號：SPRA953）JESD51-2a描述的環(huán)境中JESD51-7的規(guī)定，在一個JEDEC標(biāo)準(zhǔn)高K電路板上進(jìn)行仿真，從而獲得自然對流條件下的結(jié)至環(huán)通過在封裝頂部模擬一個冷板測試來獲得結(jié)至外殼（頂部）的熱阻。不存在特定的JEDEC標(biāo)準(zhǔn)測試，但可在ANSISEMI標(biāo)準(zhǔn)G30-88中找到內(nèi)容接近的說明。按照J(rèn)ESD51-8中的說明，通過在配有用于控制PCB溫度的環(huán)形冷板夾具的環(huán)境中進(jìn)行仿真，以獲得結(jié)至電路板的熱阻結(jié)至頂部的特征參數(shù)，ψJT)，估算真實系統(tǒng)中器件的結(jié)溫，并JESD51-2a（6章和第7章）中描述的程序從仿真數(shù)據(jù)中提取出該參數(shù)以便獲得θJA。結(jié)至電路板的特征參數(shù)，(ψJB)，估算真實系統(tǒng)中器件的結(jié)溫，并使用JESD51-2a（第6章和第7章）中描述的程序從仿真數(shù)據(jù)中提取出該參數(shù)以便獲得θJA。通過在外露（電源）焊盤上進(jìn)行冷板測試仿真來獲得結(jié)至外殼（底部）熱阻。不存在特定的JEDEC標(biāo)準(zhǔn)測試，但可在ANSI標(biāo)準(zhǔn)G30-88中找到了內(nèi)容接近的說明MENDEDOPERATINGoveroperating-airtemperaturerange(unlessotherwisedimminginputfrequencydimmingminimumon-timeInputVHigh-sideMOSFETon-Peak-to-peakinductorOperatingjunctionELECTRICAL–40°C≤TJ≤125°C,VVN=12V(unlessotherwiseTESTSUPPLYVOLTAGE(VIN InputV InternalundervoltagelockoutNovoltagehysteresis,risingandV ShutdownsupplyVEN=0V,TA=25°C,3.5V≤VVIN≤60 Non-switchingsupplyVVSENSE=210mV,ENABLEANDUVLO(EN EnablethresholdNovoltagehysteresis,risingandfalling,VInputVREFthreshold+50VREFthreshold–50HysteresisVOLTAGE Voltage3.5≤VVIN≤60V,TJ=3.5≤VVIN≤60V,-40°C≤TJ≤HIGH-SIDE VVIN=3.5V,(VBOOT–VPH)=3VVIN=12V,(VBOOT–VPH)=6ERRORInput Erroramplifiertransconductance–2μA<ICOMP<2μA,VCOMP=1ErroramplifierdcVVSENSE=0.2ErroramplifierErroramplifierVCOMP=1V,100mVCOMPtoswitchcurrentCURRENTCurrentlimitTJ=ATHERMAL ThermalThermalshutdownTIMINGRESISTORANDEXTERNALCLOCK(RT/CLK SwitchingfrequencyrangeusingRT SwitchingRRT=200SwitchingfrequencyrangeusingCLKMinimumCLKinputpulseRT/CLKhighVRT/CLKlowVRT/CLKfallingedgetoPHrisingedgeMeasuredat500kHzwithRTresistorinPhaseloop(PLL)lock-infSW=500DIMMING(PDIM) High-levelinputV Low-levelinputVTHERMALFOLDBACKPROTECTION(rampvalleyvoltage0ramppeakvoltageVfrequencyCurrentDEVICEMSOP-(Top129384756PIN1OAbootstrapcapacitorisrequiredbetweenBOOTandPH.Ifthevoltageonthiscapacitorisbelowtheminimumrequiredbytheoutputdevice,theoutputisdtoswitchoffuntilthecapacitorisrefreshed.8OErroramplifieroutput,andinputtotheoutputswitchcurrentcomparator.Connectfrequencycompensationcomponentstothispin.3IEnablepin,internalpull-upcurrentsource.Pullbelow1.2-Vtodisable.Floattoenable.Adjusttheinputundervoltagelockoutwithtworesistors.9–4Idimminginputpin.ThedutycycleofthesignallinearlycontrolstheaveragecurrentoutputofOThesourceoftheinternalhigh-side–GNDpinmustbeelectricallyconnectedtotheexposedpadontheprintedcircuitboardforproper5IResistortimingandexternalclock.Aninternalamplifierholdsthispinatafixedvoltagewhenusinganexternalresistortogroundtoprogramtheswitchingfrequency.IfthepinispulledabovethePLLupperthreshold,amodechangeoccursandthepin esasynchronizationinput.Theinternalamplifierisdisabledandthepin esahighimpedanceclockinputtotheinternalPLL.Iftheclockingedgesstop,theinternalamplifierisre-enabledandthemodereturnstotheresistor-programmedfunction.6ITemperaturefold-backpin.AnNTCthermistorconnectedfromthispintogroundprovidesathermalfeedbacktodecreasetheaverageLEDcurrentasthesensedLEDtemperatureincreases.Itismendedtobypassthispinwithacapacitorwithavalueof0.01μF(orlarger)to2IInputsupplyvoltage,3.5Vto607IInvertingnodeofthetransconductance(gM)errorFUNCTIONALBLOCKDTYPICALVINVIN=12BOOT–PH=3VBOOT–PH=6StaticStaticD?to?S0?40?25?10 203550658095110

VINVIN=12VoltageVoltageReference?40?25

203550658095110JunctionTemperature JunctionTemperatureFigure1.On-vs.Junction Figure2.ReferenceVoltagevs.JunctionVINVIN=12SwitchSwitchCurrentLimit4?40?25?10 20355065

95110

VINVIN=12VRRT=200kSwitchingFrequency?40?25?10 203550658095110JunctionTemperature JunctionTemperatureFigure3.SwitchCurrentvs.Junction Figure4.SwitchingFrequencyvs.JunctionSwitchingSwitchingFrequency

SwitchingFrequencySwitchingFrequencyVIN=12VTJLowFrequencyTJHighFrequency

TimingandExternalClock(RT/CLK TimingandExternalClock Figure5.SwitchingFrequencyvs.RT/CLKFigure6.SwitchingFrequencyvs.RT/CLKVIN=VIN=12ErrorAmplifierTransconductanceEnableThresholdEnableThreshold ?40?25?10 203550658095110

?40?25?10 203550658095110JunctionTemperature JunctionTemperatureFigure7.ErrorAmplifierTransconductancevs.Junction Figure8.EnableVoltagevs.JunctionTemperatureVINVIN=12ShutdownShutdownQuiescentCurrent?40?25?10 203550658095110JunctionTemperature

2QuiescentCurrentQuiescentCurrent100

TTJ InputVoltageFigure9.ShutdownQuiescentCurrentvs.Junction Figure10.ShutdownQuiescentCurrentvs.InputVoltageVINVIN=12VVEN_THRESHOLD–50mVEnableEnableCurrent?40?25?10 2035

658095110

VINVIN=12VVEN_THRESHOLD+50mVEnableEnableCurrent?40?25?10 2035

658095110JunctionTemperature JunctionTemperature Figure11.EnableCurrentvs.Junction Figure12.EnableCurrentvs.JunctionInputInputSupplyCurrent

TYPICALCHARACTERISTICS VIN=12VVVIN=12VVVSENSE=210mVTJ=25°CVVSENSE=210mVInputInputSupplyCurrent?40?25?10 203550658095110 10152025303540455055JunctionTemperature Figure13.InputSupplyCurrentvs.Junction Figure14.InputSupplyCurrentvs.Input InputVoltageInputVoltageUVLOBOOT?PHBOOT?PHUVLO

?40?25?10 203550658095110

?40?25?10 203550658095110JunctionTemperature JunctionTemperatureFigure15.BOOT-PHUVLOvs.Junction Figure16.InputVoltageUVLOvs.JunctionFigure17.PDIM Figure18.PDIMFigure19.Enable Figure20.EnableFigure21.SEandHigh-SideTheTPS92510isa60-V,1.5-A,step-down(buck)regulatorwithanintegratedhigh-sideN-channelMOSFET.Toimproveperformanceduringlineandloadtransientsthedeviceimplementsaconstantfrequency,peak-currentmodecontrolwhichreducesoutputcapacitanceandsimplifiesexternalfrequencycompensationdesign.Thewideswitchingfrequencyof100kHzto2500kHzallowsforefficiencyandsizeoptimizationwhenselectingtheoutputfiltercomponents.TheswitchingfrequencyisadjustedusingaresistortogroundontheRT/CLKpin.Thedevicehasaninternalphaselockloop(PLL)ontheRT/CLKpinthatisusedtosynchronizethepowerswitchturnontoafallingedgeofanexternalsystemclock.TheTPS92510hasadefaultstartupvoltageofapproximay2.5V.TheENpinhasaninternalpull-upcurrentsourcethatcanbeusedtoadjusttheinputvoltageundervoltagelockout(UVLO)thresholdwithtwoexternalresistors.Inaddition,thepullupcurrentprovidesadefaultcondition.WhentheENpinisfloatingthedeviceoperates.Theoperatingcurrentis138μAwhennotswitchingandundernoload.Whenthedeviceisdisabled,thesupplycurrentis1.3μA.Theintegrated200m?high-sideMOSFETallowsforhighefficiencypowersupplydesignscapableof1.5Aofcontinuouscurrenttoaload.TheTPS92510reducestheexternalcomponentcountbyintegratingthebootrechargediode.Thebiasvoltagefortheintegratedhigh-sideMOSFETisdbyacapacitorontheBOOTtoPHpin.ThebootcapacitorvoltageismonitoredbyanUVLOcircuitandturnsthehigh-sideMOSFEToffwhenthebootvoltagefallsbelowapresetthreshold.TheTPS92510canoperateathighdutycyclesbecauseofthebootUVLO.DETAILEDStart-TheVINandENUVLOconditionsmustbesatisfiedbeforetheTPS92510isallowedtoswitch.WhentheENpinisheldlowthedeviceentersalow-powershutdownmode,andsomeinternalcircuitsaredeactivatedtoconservepower.WhenENreturnshighthesecircuitsareenabled,whichresultsinadelayofapproximay50μs(typical)beforeswitchingstarts.Duringstart-uptheTPS92510operatesinaminimumpulsewidthmode,whichisanopen-loopcontrol.AtthestartofeachswitchingcycletheinternaloscillatorinitiatesaSETpulse.Thehigh-sideMOSFETturnsonwithaminimumpulsewidthof300ns(typical),independentoftheCOMPvoltage.Thedevicedoesnotpulseskip.WhileoperatinginminimumpulsewidthmodetheLEDbypasscapacitorisbeingcharged,causinganin-rushcurrent.Also,theCOMPvoltagebeginstoriseastheerroramplifieroutputcurrentchargesthecompensationnetwork.WhentheCOMPvoltagereachesapproximay0.7V,theerroramplifierisensuredtobeoutofsaturationandtohavesufficientgaintoregulatetheloop.TheTPS92510thentransitionsfromminimumpulsewidthmodetoregulationmode.Duringregulationmodetheerroramplifierisnowinclosed-loopcontrolofthesystem.Thegainoftheerroramplifierquicklyincreasesthedutycycle,whichcausestheoutputvoltagetoincrease.OncetheoutputvoltageapproachestheforwardvoltageoftheLEDstringtheLEDcurrentquicklybeginstoincreaseuntilitreachesregulation.ThereisaslightdelayfromthetimetheVINandENUVLOconditionsaresatisfieduntilthetimetheerroramplifierhascontrolofthefeedbackloop.ThisdelayisaresultofthetimeittakesCOMPtochargethecompensationcomponentsto0.7V.ThisdelaycanbeapproximatedasshowninEquation1.tDELAY

C1istheintegratorcapacitorfromCOMPtoR1istheresistorinserieswiththeintegrator DETAILEDDESCRIPTION(Thepeakin-rushcurrentcanbecalculatedtoafirstapproximationusingEquationVINtONmintON(min)istheminimumon-timeandcanbebetween200nsand300 MinimumPulseWidthTheTPS92510isdesignedtooutputaminimumpulsewidthduringeachswitchingcycleof280ns(typical).Thecontrolloopcannotregulatethesystemtoanon-timelessthanthisamount,anditdoesnotskippulses.Whenattemptingtooperatebelowtheminimumon-timethesystemlosesregulationandtheLEDcurrentincreases.Thisputsapracticallimitationonthesystemoperatingconditions,asshowninEquation3.

VOUTequalstheforwardvoltageoftheLEDstringplusthereference Thesystemcanavoidthisoperatingconditionbylimitingthe uminputvoltageasshowninEquation3.Iftheinputvoltagecannotbelimitedduetoapplication,thentheswitchingfrequencycanbelowered,ortheoutputvoltageincreased.Thisregionofoperationtypicallyoccurswithhighinputvoltages,highoperatingfrequencies,andlowoutputvoltages(oneLED).EnableandAdjustingUndervoltageTheTPS92510isenabledwhentheVINpinvoltageisabove2.5VandwhentheENpinvoltageisaboveV.TheVINpinvoltagethresholdhasnohysteresis.Figure22showshowtousetheENpintoadjusttheinputvoltageUVLOtoahigherthresholdandincreasetheinputvoltagehysteresis.TheENpinhasaninternalpull-upcurrentsource,I1,of0.9μAthatprovidesadefaultONstatewhentheENpinisfloating.OncetheENpinvoltageexceeds1.25V,anadditional2.9μAofhysteresis,IHYS,isadded.Thisadditionalcurrentprovidessomeinputvoltagehysteresis.UseEquation4tosettheexternalhysteresisfortheinputvoltage.UseEquation5tosettheinputstartvoltage.WhentheENpinisheldlowtheinternalregulatorsareshutdownandthedeviceentersalow-powermode.Inaddition,theerroramplifieroutputdischargestheCOMPvoltagethroughadiodepathtoGND.22.9 0.93+1.25VR1

UDGFigure22.AdjustableUndervoltageLockoutVHYSVENI1RESDIHYSRESDIHYS R2

DETAILEDDESCRIPTION( R1VENRESDI1IHYS VHYSVSTARTRESDFixedFrequency

TheTPS92510usesanadjustable,fixed-frequency,peakcurrentmodecontrol.Eachswitchingcycleaninternaloscillatorinitiatestheturn-onoftheMOSFET.TheLEDcurrentflowsthroughthesenseresistoranddevelopsthefeedbackvoltageontheVSENSEpin.Theerroramplifieroutput(COMPpin)iscomparedtothehigh-sideMOSFETcurrent.WhentheMOSFETcurrentreachesthelevelsetbytheCOMPpinvoltagetheMOSFETisturnedoff.SlopeTheTPS92510addsacompensatingramptotheMOSFETcurrentsignal.Theslopecompensationpreventssub-harmonicoscillations.Theavailablepeakinductorcurrentremainsconstantoverthefullduty-cyclerange.ConstantSwitchingFrequencyandTimingResistor(RT/CLKTheswitchingfrequencyoftheTPS92510isadjustableoverawiderangefromapproximay100kHzto2500kHzbycingaresistorontheRT/CLKpin.TheRT/CLKpinvoltageistypically0.5Vandmusthavearesistortogroundtosettheswitchingfrequency.Todeterminethetimingforagivenswitchingfrequency,useEquation8orthecurvesinFigure5orFigure6.Toreducethesolutionsizeonetypicallysetstheswitchingfrequencyashighaspossible,buttradeoffsofthesupplyefficiency,uminputvoltageandminimumcontrollableontimeshouldbeconsidered.Theminimumcontrollableontimeistypically135nsandlimitstheumoperatinginputRRT kHz2060331.0888

SynchronizationtoanExternalSystemClockTheRT/CLKpincanbeusedtosynchronizetheregulatortoanexternalsystemclockbyconnectingasquarewavetotheRT/CLKpinthroughthecircuitnetworkasshowninFigure23.Thesquarewaveamplitudemusttransitionlowerthan0.5Vandhigherthan2.2VontheRT/CLKpinandhaveanon-timegreaterthan40nsandanoff-timegreaterthan40ns.Thesynchronizationfrequencyrangeis300kHzto2200kHz.TherisingedgeofthePHissynchronizedtothefallingedgeofRT/CLKpinsignal.TheexternalsynchronizationcircuitdefaultfrequencyissetbyconnectingtheresistorfromtheRT/CLKpintogroundshouldthesynchronizationsignalturnoff.Itis mendedtouseafrequencysetresistorconnectedasshowninFigure23througha50-?resistortoground.TheresistorshouldsettheswitchingfrequencyclosetotheexternalCLKfrequency.Itis mendedtoaccouplethesynchronizationsignalthrougha470-pFceramiccapacitortoRT/CLKpinanda4-k?seriesresistor.TheseriesresistorreducesPHjitterinheavyloadapplicationswhensynchronizingtoanexternalclockandinapplicationswhichtransitionfromsynchronizingtoRTmode.ThefirsttimetheCLKispulledabovetheCLKthresholdthedeviceswitchesfromtheRTresistorfrequencytoPLLmode.Theinternal0.5-VvoltagesourceisremovedandtheCLKpin eshighimpedanceasthePLLstartstolockontotheexternalsignal.SincethereisaPLLontheregulatortheswitchingfrequencycanbehigherorlowerthanthefrequencysetwiththeexternalresistor.ThedevicetransitionsfromtheresistormodetothePLLmodeandthenincreasesordecreasestheswitchingfrequencyuntilthePLLlocksontotheCLKfrequencywithin100microseconds.WhenthedevicetransitionsfromthePLLtoresistormode,theswitchingfrequencyslowsdownfromtheCLKfrequencyto150kHz,thenreapplythe0.5-Vvoltageandtheresistorthensetstheswitchingfrequency.ItisnotmendedthatasystemtransitionfromPLLmodetoresistormoderepeatedlyduringoperation.Whenthe47045 50LoopUDGFigure23.SynchronizingtoaSystem Figure24.PlotofSynchronizinginErrorTheTPS92510erroramplifierisatransconductanceamplifier.ItcomparestheVSENSEvoltagetotheinternal0.2-Vvoltagereference.Thetransconductance(gm)oftheerroramplifieris310μA/V.ThefrequencycompensationcomponentsareconnectedfromtheCOMPpintoground.VoltageReferenceandOutputTheinternalvoltagereferenceisaccurateto±5%overtemperature.TheLEDcurrentisprogrammedwithasenseresistorfromtheVSENSEpintoGND.Itis mendedtousea1%toleranceresistor,orbetter.DimmingTheTPS92510incorporatesa dimminginputpin,whichdirectlycontrolstheenable/disablestateoftheinternalgatedriver.WhenPDIMislow,thegatedriverisdisabled.ThePDIMpinhasa1-μApull-upcurrentsource,whichcreatesadefaultONstatewhenthePDIMpinisfloating.WhenPDIMgoeslowandthegatedrivershutsoff,andtheLEDcurrentquicklyreducestozero.TheTPS92510usesasample-and-holdswitchontheerroramplifieroutput.DuringthePDIMoff-timetheCOMPvoltageremainsunchanged.Also,theerroramplifieroutputisinternallyclampedlow.Thesetechniqueshelpthesystemrecovertoitsregulationdutycyclequickly.DutyCycleandBootstrapVoltageTheTPS92510requiresasmall0.1-μFceramiccapacitorbetweentheBOOTandPHpinstoprovidethegatedrivevoltageforthehigh-sideMOSFET.TheBOOTcapacitorisrefreshedwhenthehigh-sideMOSFETturnsoff,andthewheelingdiodeconducts.AceramiccapacitorwithanX7RorX5Rdielectricandaminimumvoltageratingof10Vis TheTPS92510isdesignedtooperateupto100%dutycycleaslongastheBOOTtoPHvoltageisgreater2.1V.IftheBOOTcapacitorvoltagedropsbelow2.1V,thentheBOOTUVLOcircuitturnsofftheMOSFET,whichallowstheBOOTcapacitortoberefreshed.ThecurrentrequiredfromtheBOOTcapacitortokeeptheMOSFETonisquitelow.Therefore,manyswitchingcyclesoccurbeforetheBOOTcapacitorisrefreshed.Inthisway,theeffectivedutycycleoftheconverterisquitehigh.Attentionmustbetakenin umdutycycleapplicationswhichexperienceextendedtimeperiodswithlittleornoloadcurrent.WhenthevoltageacrosstheBOOTcapacitorfallsbelowthe2.1VUVLOthreshold,thehigh-sideMOSFETisturnedoff,buttheremaynotbeenoughinductorcurrenttopullthePHpindowntorechargetheBOOTcapacitor.Thehigh-sideMOSFEToftheregulatorstopsswitchingbecausethevoltageacrosstheBOOTcapacitorislessthan2.1V.Theoutputcapacitorthendecaysuntilthedifferencebetweentheinputvoltageandoutputvoltageisgreaterthan2.1V,atwhichpointtheBOOTUVLOthresholdisexceeded,andthedevicestartsswitchingagainuntilthedesiredoutputcurrentisreached.Thisoperatingconditionpersistsuntiltheinputvoltageand/ortheloadcurrentincreases.Itis mendedtoadjusttheVINstopvoltagegreaterthantheBOOTUVLOtriggerconditionattheminimumloadoftheapplicationusingtheadjustableVINUVLOfeaturewithresistorsontheENpin.OvercurrentAnovercurrentfaultconditionisunlikely.Itcanbetheresultofashortedsenseresistor,oradirectshortfromVOUTtoGND.Ineithercase,thevoltageattheVSENSEpiniszero,andthiscausestheCOMPpinvoltagetorise.WhenVCOMPreachesapproximay2.2Vitisinternallyclamped,andfunctionsasaMOSFETcurrentlimit.TheTPS92510limitstheMOSFETcurrentto4A(typical).IftheshortedconditionpersiststheTPS92510junctiontemperatureincreases.Ifitincreasesabove150°C,thethermalshutdownprotectionisactivated.LEDThermalFoldbackTheTPS92510implementsathermalfoldbackprotectiontolimittheLEDtemperatureincaseofasystemfailure,suchasanincorrectlyprogrammedLEDcurrent,apoorthermaldesignorincreasingthermalimpedanceovertime.A100-μAcurrentsourcegeneratesavoltageacrossanNTCresistorthatislocatedneartheLEDload.WhentheNTCvoltagedropsbelow2VattheSEpin(duetoexcessiveLEDtemperature)thedevicebeginstomodulatetheconverteratafrequencyof5.9kHz.ThemoretheNTCvoltagedrops,thelongertheoff-timeoftheconverter.Therefore,thedeliveredoutputpowerisreduceduntiltheNTCcools,theSEvoltage(VSE)increases,andthesystemnolongerrequiresreducedoutputpower.Thethermalfoldbackprotectionslowlyreducestheoutputpower,asafunctionofthethermaltimeconstant.Thermalfoldbackprotectionisintendedforprotectiononly.Itisnotintendedtobeusedasaregulationfeature.Duringthermalfoldbacktheerroramplifieroutputisinternallyclampedlow,andtheCOMPsample-and-holdswitchisopen,preservingtheCOMPpinvoltage.Figure25showsthethermalfoldbackNormalizedNormalizedLEDCurrent0 SEVoltageFigure25.ThermalFoldback

Over-TemperatureFaultWhentheTPS92510junctiontemperaturereaches150oC,thedriverimmedia ydisablesthehigh-sideMOSFET.TheCOMPsample-and-holdswitchcloses,andtheCOMPpininternallyclampslowuntilthejunctiontemperaturedropsbyapproximay20oC.Atthistime,theCOMPclampisremovedandthedriverattemptstoAPPLICATIONOpenLEDFaultAnopencircuitcanbetheresultofanopenLEDoranopenwireconnection.Ineithercase,thevoltageattheVSENSEpin eszero,andthiscausestheCOMPpinvoltagetorise,commandingwidedutycycles.Theoutputvoltageeventuallyrisestotheinputvoltage.Thisisasafeoperatingmode,providedthattheoutputcapacitorsareratedfortheinputvoltagepotential.AsshowninFigure26,atransientvoltagesuppressor(TVS)devicefromVOUTtoGND,oradiodefromVOUTtotheVINpincanbeusedtoclamptheL-CresonantoutputvoltageringingcausedbytheinductorandtheoutputcapacitoratthemomenttheLEDstringopens,particularlyathigh-inputvoltageandhigh-outputvoltageoperatingconditions.TheTVSshouldhaveavoltageratinggreaterthanthe umoutputvoltage,sothatitdoesnotconductundernormaloperation.EitherofthesedevicescanbeusedtolimittheoutputvoltagetosafelevelsduringanopenLEDfault. 2 2PH438VSENSE5UDGFigure26.OutputVoltageAnexternalovervoltageprotectioncircuitconsistingofVZandRZshowninFigure27,canbeappliedtotheVSENSEpintoregulatetheoutputvoltagetolessthantheinputvoltagepotential. 2PH438 VSENSE59UDGFigure27.OutputVoltageShortedLED(s)Fault22Figure28.LEDCurrentLimiterDuetoaShortedEquation10showshowtoreducethepeaktransientcurrent(ΔI)byaddingaseriesinductance(LLIMIT).Typically,thebypasscapacitor(COUT)isusedtoreducethehigh-frequencyripplecurrentthroughtheLED.Addinginductanceintothispathiscounterproductive.Alternatively,thebuckinductance,orswitchingfrequencycanbeincreasedtoachievealowerLEDripplecurrent.Inthisway,theoutputcapacitorcanbereducedinvalue,whichallowsLLIMITtobesmaller.TheendresultoflowLEDripplecurrentcanstillbeachieved.Reducingtheoutputcapacitor(COUT)doesnotreducethemagnitudeofthetransientcurrent,butitdoesreducethesettlingI RDYNAMICRESROpenCurrentSenseResistorFault

Anopencurrentsenseresistorisunlikely,butmaybecausedbyafailingresistor,anopensolderjoint,oranopenPCBtrace.Asthecurrentsenseresistoropens,theoutputvoltagequicklyrisesduetotheenergystoredintheinductor,similartoanopenLEDfault.Therefore,itisnecessarytoclamptheoutputvoltage,eitherwithaTVStoGNDoradiodefromVOUTtoVIN.ItisalsonecessarytouseacurrentlimitingresistorontheVSENSEpin.Otherwise,theoutputvoltageecausestheVSENSEvoltagetobreakdownitsinternalESDstructure.TheESDdeviceshouldbelimitedto20mA.Inthiscondition,theconverterattemptstoregulatetheoutputcurrentthroughtheESDstructure,whichresultsinaverylowregulatedcurrent.Typically,theoutputvoltageoverchargesandholdstheVSENSEvoltagehighwithinafewswitchingcycles.Thedevicestopsswitching,andthereisalongoff-timebetweenconsecutivestart-upattempts.TheconsecutiveattemptsresultinlowerpeakcurrentthroughtheESDstructurethantheinitialevent.ShortedOutputAshortedoutputfaultisconsideredrare,becausethesystemdoesnotrequireanysinglecomponentfromVOUTtoGND.Therefore,asinglecomponentfailurecannotcausethisfaultcondition.Ifthisfailuremodeweretooccuritwouldmostlikelybeduetoamechanicalshort,oraforeignobject.Intheunlikelyeventofthisfailuremode,theTPS92510respondsinthefollowingway.WiththeoutputvoltageshorteddirectlytogroundtheCOMPvoltagesaturateshigh,becausethefeedbackvoltageiszero.ThecontrollerwouldnaturallycommandwidedutycyclePHpulses.However,assoonasthegatedriverturnson,veryquicklyanovercurrenteventisdetectedandthePHpulseistruncated.Thisresultsinminimumon-timepulsesatthePHnode.Dependingupontheimpedanceoftheshort,largecurrentscanbuildupintheinductor,whichnaturallyraisesthejunctiontemperatureoftheTPS92510.Theover-temperatureprotectionfeatureprotectsthedevice.Control-to-OutputTransferTheTPS92510converterusespeakcurrentmodecontrolinordertoregulatetheaverageLEDcurrent.Slopecompensationisutilizedinternallytoeliminatesub-harmonicoscillationsoverawiderangeofoperatingdutycycles.Toproperlycompensatetheclosed-loopsystemthecontroltooutputgaincharacteristicsmustbecalculated.Thecontroltooutputtransfe6rfunctionisshowninEquation167 fMRSENSEGC2O

fM

RSENSEistheLEDcurrentsense (11)117103LV 3