SNVS316H –SEPTEMBER 2004–REVISED DECEMBER …

1 VIN VIN ENBOOSTSWFBGNDVOUT C3 L1C1 C2 R1 R2 D1 D2 ONOFFP roductFolderSample &BuyTechnicalDocumentsTools &SoftwareSupport &CommunityLM2736 SNVS316H SEPTEMBER2004 REVISEDDECEMBER2014LM2736 Thin SOT 750 mA Load Step-DownDC-DCRegulator1 Features3 DescriptionThe LM2736regulatoris a monolithic,high frequency,1 ThinSOT-6 PackagePWMstep-downDC/DCconverterin a 6-pinThin V to 18 V providesall the activefunctionsto to 16 V OutputVoltageRangeprovidelocalDC/DCconve rsionwithfast transientresponseandaccurateregulationin the smallest 750 mA OutputCurrentpossiblePCBarea. 550 kHz (LM2736Y)and MHz(LM2736X)SwitchingFrequenciesWitha minimumof externalcomponentsand onlinedesignsupportthroughWEBENCH , the LM2736is 350 m NMOSS witcheasyto use. The abilityto drive750 mA loadswith an 30 nA ShutdownCurrentinternal350 m NMOS switchusingstate-of-the-art , 2% m BiCMOS technologyresultsin the InternalSoft-Startallowsfor on-timesas low as 13 ns, thussupporting Current-Mode,PWMO perationexceptionallyhighfrequencyconver sionoverthe WEBENCH OnlineDesignToolentire3 V to 18 V inputoperatingrangedownto theminimumoutputvoltageof Switching ThermalShutdownfrequencyis internallyset to 550 kHz (LM2736Y) MHz(LM2736X),allowingthe use of extremely2 Applicationssmallsurfacemountinductorsan d chipcapacitors.

2 LocalPointof LoadRegulationEventhoughthe operatingfrequenciesare veryhigh, CorePowerin HDDsefficienciesup to 90%are easyto included,featuringan ultra-lowstand-by Set-TopBoxescurrentof 30 nA. The LM2736utilizescurrent-mode BatteryPoweredDevicescontrolandinternalc ompensationto providehigh- USBP oweredDevicesperformanceregulationovera DSLM odemsinternalsoft-startcircuitryto reduceinrushcurrent, NotebookComputerspulse-by-pulsecurrentli mit,thermalshutdown, (1)PARTNUMBERPACKAGEBODYSIZE(NOM)LM2736 SOT(6) x (1) For all availablepackages,see the orderableaddendumatthe end of the LoadCurrent"X"VIN= 5 V, VOUT= V1An IMPORTANTNOTICEat the end of this datasheetaddressesavailability,warranty, changes,use in safety-criticalapplications,intellectual propertymattersand SEPTEMBER2004 Applicationand Pin Configurationand Deviceand Mechanical,Packaging,and RevisionHistoryNOTE:Pagenumbersfor previousrevisionsmay differfrompagenumbersin the (October2014)to RevisionHPage UpdatedDesignRequirementsand movedBill of (April2013)to RevisionGPage AddedESDR atingstable,FeatureDescriptionsection,De viceFunctionalModes,Applicationand Implementationsection,PowerSupplyRecomme ndationssection,Layoutsection,Deviceand DocumentationSupportsection,andMechanica l,Packaging,and 2004 2014, SEPTEMBER2004 REVISEDDECEMBER20145 Pin Configurationand FunctionsPackageDDC(R-PDSO-G6)6-LeadSOTT op ViewPin drivesthe bootstrapcapacitorisBOOST1 Iconnectedbetweenthe BOOSTand SW Powergroundpin.

3 Placethe bottomresistorof the feedbacknetworkas closeasGND2 GNDpossibleto this pin for ConnectFB to the externalresistordividerto set not allowthis pin to float or be greaterEN4 Ithan VIN+ bypasscapacitorto this the inductor,catchdiode,and 2004 2014,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback3 ProductFolderLinks:LM2736LM2736 SNVS316H SEPTEMBER2004 (unlessotherwisenoted)(1) SW + CInfrared/ConvectionReflow(15sec)220 CSolderingInformationWaveSolderingLeadte mperature(10sec)260 CTstgStoragetemperature-65150 C(1)If Military/Aerospacespecifieddevicesare required,pleasecontactthe TexasInstrumentsSalesOffice/Distributors for (HBM),V(ESD)Electrostaticdischarge 2000 Vper ANSI/ESDA/JEDECJS-001,all pins(1)(1)JEDEC documentJEP155statesthat 500-VHBM allowssafe manufacturingwith a (unlessotherwisenoted)MINNOMMAXUNITVIN31 8 VSW SW 40125 (1)DDCUNIT6 PINSR JA(2) JC(top)Junction-to-case(top) C/W JC(bot)Junction-to-case(bottom)thermalre sistancen/a(1)For moreinformationabouttraditionaland new thermalmetrics,see theIC PackageThermalMetricsapplicationreport,S PRA953.

4 (2)Thermalshutdownwill occurif the junctiontemperatureexceeds165 C. The maximumpowerdissipationis a functionof TJ(MAX), JAand TA. The maximumallowablepowerdissipationat any ambienttemperatureis PD= (TJ(MAX) TA)/ JA. All numbersapplyforpackagessoldereddirectlyo ntoa 3 x 3 PC boardwith 2oz. copperon 4 layersin still air. For a 2 layerboardusing1 oz. copperin stillair, JA= 204 2004 2014, SEPTEMBER2004 standardtypefaceare for TJ= 25 C design,test, or 25 CTJ = -40 C to 125 CPARAMETERTESTCONDITIONSUNITMIN(1)TYP(2) MAX(1) VFB/ FeedbackVoltageLineVIN= 3V to / (ON)SwitchON ResistanceVBOOST- VSW= 3V350650m ICLS witchCurrentLimitVBOOST- VSW= 0V30nA(shutdown)LM2736X(50% )IBOOSTB oostPin CurrentmALM2736Y(50% ) CurrentSink/Source10nAISWS witchLeakage40nA(1)Specifiedto TexasInstruments' AverageOutgoingQualityLevel(AOQL).(2)Typ icalsrepresentthe 2004 2014,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback5 ProductFolderLinks:LM2736LM2736 SNVS316H SEPTEMBER2004 curvestakenat VIN= 5V, VBOOST- VSW= 5V, L1 = H ("X"), L1 = 10 H ("Y"), and TA= 25 C, OscillatorFrequencyvs Temperature- "X"Figure2.

5 OscillatorFrequencyvs Temperature- "Y"Figure3. CurrentLimitvs TemperatureFigure4. VFBvs TemperatureFigure5. RDSONvs TemperatureFigure6. IQSwitchingvs Temperature6 SubmitDocumentationFeedbackCopyright 2004 2014, SEPTEMBER2004 REVISEDDECEMBER2014 TypicalCharacteristics(continued)All curvestakenat VIN= 5V, VBOOST- VSW= 5V, L1 = H ("X"), L1 = 10 H ("Y"), and TA= 25 C, LineRegulation- "X"Figure8. LineRegulation- "Y"VOUT= V, IOUT= 500 mAVOUT= V, IOUT= 500 mAFigure9. LineRegulation- "X"Figure10. LineRegulation- "Y"Copyright 2004 2014,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback7 ProductFolderLinks:LM273600 VINVDTONttInductorCurrentD = TON/TSWVSWTOFFTSWILIPKSWV oltageLM2736 SNVS316H SEPTEMBER2004 LM2736deviceis a constantfrequencyPWMbuckregulatorIC that deliversa 750 mA a presetswitchingfrequencyof either550 kHz (LM2736Y)or MHz(LM2736X).Thesehighfrequenciesallowth e LM2736deviceto operatewith smallsurfacemountcapacitorsand inductors,resultinginDC/DCconvertersthat requirea minimumamountof internallycompensated,so it is simpleto use,and requiresfew LM2736deviceusescurrent-modecontrolto regulatethe followingoperatingdescriptionof the LM2736devicewill referto the SimplifiedBlockDiagram(FunctionalBlockDi agram) and to the waveformsin Figure11.

6 The LM2736devicesuppliesa regulatedoutputvoltagebyswitchingthe internalNMOS controlswitchat constantfrequencyand switchingcyclebeginsat the fallingedgeof the resetpulsegeneratedby the pulsegoeslow, theoutputcontrollogicturnson the on-time,the SW pin voltage(VSW)swingsup to approximatelyVIN, and the inductorcurrent(IL) increaseswith a measuredby thecurrent-senseamplifier,whichgenerates an outputproportionalto the the regulator s correctiverampand comparedto the erroramplifier s output,whichis proportionalto the differencebetweenthe feedbackvoltageand VREF. Whenthe PWMcomparatoroutputgoeshigh,theoutputswi tchturnsoff untilthe switchoff-time,inductorcurrentdischarges throughSchottkydiodeD1, whichforcesthe SW pin to swingbelowgroundby the forwardvoltage(VD) of the regulatorloop adjuststhe duty cycle(D) to maintaina LM2736 Waveformsof SW Pin Voltageand InductorCurrent8 SubmitDocumentationFeedbackCopyright 2004 2014,TexasInstrumentsIncorporatedProduct FolderLinks:LM2736LR1R2D1D2 BOOSTO utputControlLogicCurrentLimitThermalShut downUnderVoltageLockoutCorrective RampResetPulsePWMC omparatorCurrent-Sense AmplifierRSENSE++ :SwitchInternalCompensationSWENFBGNDE rror Amplifier-+ +-CBOOSTVOUTCINVINVINISENSE+-+-+ + SEPTEMBER2004 overvoltagecomparatorcomparesthe FB pin voltageto a voltagethat is 10%higherthanthe FB pin voltagegoes10%abovethe internalreference,the internalNMOS controlswitchis turnedoff, whichallowsthe outputvoltageto (UVLO)preventsthe LM2736devicefromoperatinguntil the (typ).

7 The UVLO thresholdhas approximately440mVof hysteresis,so the part will operateuntil V(typ).Hysteresispreventsthe part fromturningoff duringpowerup if VINis LM2736deviceusescycle-by-cyclecurrentlim itingto protectthe ,a currentlimit comparatordetectsif the A (typ),and turnsoff the switchuntilthe next powerdissipationby turningoff the outputswitchwhenthe IC junctiontemperatureexceeds165 C. Afterthermalshutdownoccurs,the outputswitchdoesn t turn on until the junctiontemperaturedropsto approximately150 2004 2014,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback9 ProductFolderLinks:LM2736LM2736 SNVS316H SEPTEMBER2004 / ShutdownModeThe LM2736devicehas a shutdownmodethat is controlledby the enablepin (EN).Whena logiclow voltageisappliedto EN, the part is in shutdownmodeand its quiescentcurrentdropsto typically30 nA. Switchleakageaddsanother40 nA fromthe voltageat this pin shouldneverexceedVIN+ increaseat a controlledrate duringstartup. Duringsoft-start,the erroramplifier sreferencevoltagerampsfrom0 V to its nominalvalueof in approximately200 s.

8 Thisforcestheregulatoroutputto rampup in a morelinearand controlledfashion, 2004 2014, SEPTEMBER2004 REVISEDDECEMBER20148 Applicationand ImplementationNOTEI nformationin the followingapplicationssectionsis not partof the TI componentspecification,and TI doesnot warrantits accuracyor s customersareresponsiblefor determiningsuitabilityof componentsfor test theirdesignimplementationto diodeD2 in Figure12 are usedto generatea voltageVBOOST. VBOOST- VSWis the gatedrivevoltageto the properlydrivethe internalNMOS switchduringits on-time,VBOOST needsto be at V greaterthanVSW. Althoughthe LM2736devicewill operatewith this minimumvoltage,it maynot havesufficientgatedriveto supplylargevaluesof ,it isrecommendedthat VBOOSTbe V aboveVSWfor best VSWshouldnot exceedthe maximumoperatinglimit of V > VBOOST VSW> V for best VOUTC hargesCBOOSTW henthe LM2736devicestartsup, internalcircuitryfromthe BOOSTpin suppliesa maximumof 20 mA toCBOOST. This currentchargesCBOOSTto a voltagesufficientto turn the switchon.

9 The BOOSTpin will continuetosourcecurrentto CBOOST until the voltageat the feedbackpin is variousmethodsto deriveVBOOST:1. Fromthe inputvoltage(VIN)2. Fromthe outputvoltage(VOUT)3. Froman externaldistributedvoltagerail (VEXT)4. Froma shuntor serieszenerdiodeIn theFunctionalBlockDiagram, capacitorCBOOSTand diodeD2 supplythe gate-drivecurrentfor the chargedvia diodeD2 by VIN. Duringa normalswitchingcycle,whenthe internalNMOS controlswitchis off (TOFF) (referto Figure11), VBOOST equalsVINminusthe forwardvoltageof D2 (VFD2),duringwhichthe currentin the inductor(L) forwardbiasesthe SchottkydiodeD1 (VFD1). Thereforethe voltagestoredacrossCBOOSTisVBOOST- VSW= VIN- VFD2+ VFD1(1)Whenthe NMOS switchturnson (TON), the switchpin risestoVSW= VIN (RDSONx IL),(2)forcingVBOOSTto rise thus reversebiasingD2. The voltageat VBOOSTis thenVBOOST= 2 VIN (RDSONx IL) VFD2+ VFD1(3)whichis approximately2 VIN- V(4)for gate-drivevoltageof the NMOS switchis approximatelyCopyright 2004 2014,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback11 ProductFolderLinks:LM2736 VINBOOSTSWGNDCBOOSTLD1D2D3 VBOOSTVINCINCOUTVOUTLM2736 SNVS316H SEPTEMBER2004 (continued)VIN- V(5)An alternatemethodfor chargingCBOOSTis to connectD2 to the outputas shownin Figure12.

10 The outputvoltageshouldbe V and V, so that propergatevoltagewill be appliedto the circuit,CBOOST providesa gatedrivevoltagethat is slightlyless applicationswherebothVINand VOUTare V, or less than3 V, CBOOST cannotbe VINand VOUTare V, CBOOSTcan be chargedfromVINor VOUT minusa zenervoltageby placinga zenerdiodeD3 in serieswith D2, as shownin Figure13. Whenusingaserieszenerdiodefromthe input,ensurethat the regulationof the inputsupplydoesn t createa voltagethat fallsoutsidethe recommendedVBOOST voltage.(VINMAX VD3) < V(6)(VINMIN VD3) > V(7)Figure13. ZenerReducesBoostVoltagefromVINAn alternativemethodis to placethe zenerdiodeD3 in a shuntconfigurationas shownin Figure14. A small350mW to 500 mW V zenerin a SOTor SODpackagecan be usedfor this smallceramiccapacitorsuchas a V, F capacitor(C4)shouldbe placedin parallelwiththe internalNMOS switchturnson, a pulseof currentis drawnto chargethe Fparallelshuntcapacitorensuresthat the VBOOST voltageis maintainedduringthis shouldbe chosento provideenoughRMScurrentto the zenerdiode(D3)and to the BOOSTpin.