AN-1820LM5032 Interleaved Boost Converter

1 ApplicationReportSNVA335A May2008 highinputvoltagerange,thecontrollerconta insalltheauxiliaryfeaturesneededtocontro la (BOM).. (IL) May2008 RevisedMay2013AN-1820LM5032 InterleavedBoostConverterSubmitDocumenta tionFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedLM5032+ basicboostconverterconvertsa DCvoltagetoa realizedbysplittingtheoutputcurrentintot wopaths,substantiallyreducingI2R ,currentrampsupin L1witha slopedependingontheinputvoltage, offduringthistimesincetheoutputvoltageis , L1rampsdownwitha , ,theeffectiveripplefrequencyis twicethatofa , deliveredtotheloadduringeachswitchingper iod, alltheenergystoredin theinductoris deliveredtotheloadduringeachswitchingcyc le,themodeofoperationis classifiedasdiscontinuousconductionmode( DCM).

2 Onlypartoftheenergyis deliveredtotheload,thentheconverteris saidtobeoperatingin continuousconductionmode(CCM).Figure2 a fundamentalfactorin May2008 RevisedMay2013 SubmitDocumentationFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedCCMDCMB oundaryConditionIp0Ip0Ip0 DTSTS=1 (IL) usingCCMistheinherentstabilityproblemsca usedbytheright-half-planezeroin thetransferfunction. However,theswitchandoutputdiodepeakcurre ntsarelargerwhentheconverteris operatingin , ,thisdesignis ,theinputandoutputcapacitors, ,it is channeledthroughtwopowerpaths,agoodstart ingpointis ,thedesignstartswitha ,a , , ,therearemanytrade-offspossible, ,theoutputvoltage,andthevoltagedropsacro sstheoutputdiodeandswitch, , certainpercentageoftheaverageinductorcur rent, thencalculatedusingtheripplecurrent,swit chingfrequency,inputvoltage, , , May2008 RevisedMay2013AN-1820LM5032 InterleavedBoostConverterSubmitDocumenta tionFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedL(crit) =fS x IOUT(VIN(MIN) - VON) x DMAX x (1 - DMAX)IPEAK =IOUT1 - DMAXIL(avg-critical) ='IPEAK2L(MIN)

3 =fS x 'IL(VIN(MIN) - V(ON)) x DMAXIPEAK = IL(avg) +'IL2IL(avg) = x IOUT1 - DMAXDmin =VOUT + Vd - VIN(MAX)VOUT + Vd - V(ON)Dmax =VOUT + Vd - VIN(MIN)VOUT + Vd - V(ON) (1)(2)Where,VOUTis theoutputvoltage,Vdis theforwardvoltagedropoftheoutputdiode,an dV(ON)is (MAX)is themaximuminputvoltage,andVIN(MIN)is (maximum)perphasecanbecalculatedknowingt heoutputcurrent,IOUT,rememberingthatthec urrentperphaseis Equation3:(3)Asa startingpointassumethepeakinductorcurren trippleperphase, ILtobea certainpercentageoftheaverageinductorcur rentcalculatedin Equation3. A goodstartingvalueof ILis about40%ortheoutputcurrent,whichis 20% ,sosomeiterationmaybenecessaryin givenby:(4)Knowingtheswitchingfrequency, fstherequiredinductancevalueperphasecanb eselectedusing:(5)AttheboundarybetweenCC MandDCMmodesofoperation,thepeakinductorc urrentperphase,IPEAK isthesameasthepeak-to-peakinductorcurren trippleperphase, IL, asshownin Figure2.

4 Therefore,theaverageinductorcurrentatthe boundaryis givenby:(6)FromEquation3 andEquation6:(7)Thecriticalvalueoftheind uctanceperphasetomaintaintheconverterin continuousmoderelatedtooutputcurrentis givenbyEquation5 andEquation7.(8)Knowingtheminimumloadcur rentin a particulardesignL ,therearetrade-offsbetweenminimumloadcur rent,percentripple, boostconverter, (ESR) ,calculatetheworstcasedutycycleforripple ,whichis usuallythemaximumdutycycle(forthisvalue, seeFigure3). Then,readthey axisvalueornormalizedrmsripplein theoutputcapacitorfromFigure3 May2008 RevisedMay2013 SubmitDocumentationFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedVINL x fSIRIPPLE(Normalized) ='VOUT =IOUT(MAX) x (1 - DMIN)fS x COUT+ IPEAK x ESR0 Phase1 , , ,useEquation9 todeterminethecapacitancenecessarytoinsu rea ,theESRis thedominateterm,whichdeterminesthecapaci tor s , , fs is doublethefrequencyofanindividualphase,si ncebothphasesarecombinedattheoutputcapac itor.

5 (9)It is interestingtoobservefromFigure3 thatthereductionin RMS(andpeak-to-peak) ,rippleis nearlyperfectlycanceled,whichoccurswhenV INis in serieswiththeinputsupplyin a boostconverter,inputcapacitorselectionis two-phasedesign,thereis a furtherreductionin inputrippleduetoripplecancellation,allow inga smallerinputcapacitorthanin a Figure4. Thisgraphis normalizedaccordingto(10)wherefsis May2008 RevisedMay2013AN-1820LM5032 InterleavedBoostConverterSubmitDocumenta tionFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedPMOSFET =x RDS(ON) x D x + VIN(MAX) x Qg x fS +IOUT(MAX)2 x (1 - D) x VIN(MAX) x IOUT x fS x (tg + tF)(1 - D)0 CYCLE2 Phase1 axisofthegraphin reasonablelimitsandresultsin theoutputcapacitorcase,determinetheworst casedutycyclefora (ON) moredetailedcalculationforthepowerdissip atedin eachMOSFETis givenby.

6 (11)Thefirsttermis theI2R in thedenominatoris basedonvoltageandcurrentratings, Schottkyrectifierif voltageratingspermit,otherwiseanultra-fa strectifieris May2008 RevisedMay2013 SubmitDocumentationFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedRLOAD x (1 - D)22 x S x LfRHPZ =RLOAD x VIN22 x S x L x VOUT2= a right-half-planezeroin toinsuretheloopgaincrosseszeroatlowertha n1/4theswitching(perphase) givenby:(12)11 PrototypeA limitofabout14ampsofinputcurrent, ,thespecificationsare:VIN= 12to45voltsVOUT= 48voltsIOUT= < 50mVFora completeschematicoftheprototype, builtaroundtheLM5032,a 2 thisdesignsinceweareimplementinga two-phase,singleoutputconverter, ,sincethisinsurescurrentbalancein ,InductorsL2andL3, May2008 RevisedMay2013AN-1820LM5032 InterleavedBoostConverterSubmitDocumenta tionFeedbackCopyright 2008 2013, May2008 RevisedMay2013 SubmitDocumentationFeedbackCopyright 2008 2013, ,a eachphase,reducingI2R alreadyin useastheerroramplifierreference,thecircu itonlyaddsa ,R10,andthecurrentsenseresistorsforma voltagedividerfromthe2 , theDCoffsetis , muchlargerthanR10andwithR10muchlargertha nthesenseresistors.

7 A switchingbiassupplywasconstructedwithadj ustablecontrollerU2, Figure7, thiscircuitis verysmallandoffersa goodsolutionfora a linearregulatororzenerdiodewereused,in wouldbenecessarytodropabout31voltsfromth einputsupplyatVin(max).Withanoverheadcur rentof500mA,a ,convertingtheerroramplifiertoa May2008 RevisedMay2013AN-1820LM5032 InterleavedBoostConverterSubmitDocumenta tionFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedLOAD (A)EFFICIENCY (%) = 12 VVin = 24 VVin = 36 VVin = Figure7, thetwopowerinductorsoccupythetoppartofth eleftphotograph, locatedin locatedneartheupperright, May2008 RevisedMay2013 SubmitDocumentationFeedbackCopyright 2008 2013, Figure8 takenattheDCM/CMboundary,efficienciesran gefrom95%to98%uptothefull4 ampsofoutputcurrent,andovera ,butthisis compact, doublethefrequencyoftheindividualphasesa ndata lowerRMScurrentvalue,thedesignerhasthech oiceofsmalleroutputcapacitorswiththesame rippleasa singlephaseconverter, a andFigure4 showstheoutputrippleoftheprototypethatis a functionofdutycycle.

8 Thedegreeofrippleoverlapis alsoa nearperfectcancellationofrippleat50% converterwithlittletonooutputrippleif thedesignercanlimitVintothepropervaluefo r50% ,rippleis reducedbyasmuchas50% ,inductorselectionis ,whichmakeseachinductorsmaller,butresult sin thesinglephasedesign, May2008 RevisedMay2013AN-1820LM5032 InterleavedBoostConverterSubmitDocumenta tionFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedBillofM aterials(BOM) (BOM) (BOM)QtyPartsValueDescriptionPartNumberM anufacturer7C1,C2,C3,C4, F 50VX7R10%1210C3225X7R1H225 KTDKC17,C18,C198C5,C6,C10,C12, F 100VX7R10%0805C2012X7R2A104 KTDKC21,C22,C23,C252C7, F 10%50VX7R080508055C103 KAT2 AAVX1C922 FCAPCER22 F 10V10%X7R1210 GRM32ER71A226KE20 LMURATA3C11,C13,C14100pFCAPCER100pF50VC0 G5%0805C2012C0G1H101 JTDK2C15,C16150 FCAP150 F F 100VX7R10%1206C3216X7R2A104 KTDK1C24470pFCAPCER470pF50V5% ,J2,J3,J4I/OTERMSCREWVERTSNAP-INPCMNT769 3 KEYSTONE3J5,J6,J7 TPTESTPOINTPCMULTIPURPOSEWHT5012 KEYSTONE1L1330 HINDUCTOR330 H LEADFREESDR0503-331 KLBOURNS2L2,L315 HINDUCTOR15 H, ,28 ARMSSER2807H-153 KLCOILCRAFT2Q1.

9 Q2 SUD50N06-9LN-CHANNELMOSFETsN-CH60V50 ASUD50N06-09L-E3 VISHAY1R1160kRES160 KOHM1/8W1%0805 SMDCRCW0805160 KFKEAVISHAY10R12,R13,R14, ,R16,R17,R18,R19,R20,R211R2110kRES110 KOHM1/8W1%0805 SMDCRCW0805110 KFKEAVISHAY2R23, ,R10, , , May2008 RevisedMay2013 SubmitDocumentationFeedbackCopyright 2008 2013,TexasInstrumentsIncorporatedIMPORTA NTNOTICET exasInstrumentsIncorporatedanditssubsidi aries(TI)reservetherighttomakecorrection s,enhancements,improvementsandotherchang estoitssemiconductorproductsandservicesp erJESD46,latestissue,andtodiscontinueany productorserviceperJESD48, (alsoreferredtohereinas components ) aresoldsubjecttoTI s ,in accordancewiththewarrantyin TI s ,testingofallparametersofeachcomponentis productsandapplications, ,eitherexpressorimplied,is grantedunderanypatentright,copyright,mas kworkright,orotherintellectualpropertyri ghtrelatingtoanycombination,machine,orpr ocessin licensetousesuchproductsorservicesora licensefroma thirdpartyunderthepatentsorotherintellec tualpropertyofthethirdparty,ora TIdatabooksordatasheetsis permissibleonlyif reproductionis withoutalterationandis accompaniedbyallassociatedwarranties,con ditions,limitations, is solelyresponsibleforcompliancewithallleg al,regulatoryandsafety-relatedrequiremen tsconcerningitsproducts.

10 AndanyuseofTIcomponentsin itsapplications, hasallthenecessaryexpertisetocreateandim plementsafeguardswhichanticipatedangerou sconsequencesoffailures,monitorfailuresa ndtheirconsequences, , ,TI s goalis , FDAC lassIII(orsimilarlife-criticalmedicalequ ipment)unlessauthorizedofficersofthepart ieshaveexecuteda enhancedplastic solelyattheBuyer's risk,andthatBuyeris solelyresponsibleforcompliancewithallleg alandregulatoryrequirementsin , , , :TexasInstruments,PostOfficeBox655303,Da llas,Texas75265 Copyright 2013,TexasInstrumentsIncorporat