higherwww.mm.com

UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010GreenPhase-ShiftedFull-BridgeControllerWithSynchronousRectificationCheckforSamples:UCC289501FEATURESAPPLICATIONSPhase-ShiftedFull-BridgeConvertersEnhancedWideRangeResonantZeroVoltageSwitching(ZVS)CapabilityServer,TelecomPowerSuppliesIndustrialPowerSystemsDirectSynchronousRectifier(SR)ControlHigh-DensityPowerArchitecturesLight-LoadEfficiencyManagementIncludingSolarInverters,andElectricVehicles–BurstModeOperation–DiscontinuousConductionMode(DCM),DESCRIPTIONDynamicSROn/OffControlwithProgrammableThresholdTheUCC28950enhancedphase-shiftedcontrollerbuildsuponTexasInstrument'sindustrystandard–ProgrammableAdaptiveDelayUCCx895phase-shiftedcontrollerfamilywithAverageorPeakCurrentModeControlwithenhancementsthatofferbestinclassefficiencyinProgrammableSlopeCompensationandtoday'shighperformancepowersystems.
TheVoltageModeControlUCC28950implementsadvancedcontrolofthefull-bridgealongwithactivecontroloftheClosedLoopSoftStartandEnableFunctionsynchronousrectifieroutputstage.
ProgrammableSwitchingFrequencyupto1MHzwithBi-DirectionalSynchronizationTheprimary-sidesignalsallowprogrammabledelaystoensureZVSoperationoverwide-loadcurrentand(+/-3%)Cycle-by-CycleCurrentLimitinputvoltagerange,whiletheloadcurrentnaturallyProtectionwithHiccupModeSupporttunesthesecondary-sidesynchronousrectifiers150-AStart-UpCurrentswitchingdelays,maximizingoverallsystemVDDUnderVoltageLockoutefficiency.
WideTemperatureRange-40°Cto125°CUCC28950TypicalApplication1Pleasebeawarethatanimportantnoticeconcerningavailability,standardwarranty,anduseincriticalapplicationsofTexasInstrumentssemiconductorproductsanddisclaimerstheretoappearsattheendofthisdatasheet.
PRODUCTIONDATAinformationiscurrentasofpublicationdate.
Copyright2010,TexasInstrumentsIncorporatedProductsconformtospecificationsperthetermsoftheTexasInstrumentsstandardwarranty.
Productionprocessingdoesnotnecessarilyincludetestingofallparameters.
UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comDESCRIPTION(CONT.
)TheUCC28950alsooffersmultiplelight-loadmanagementfeaturesincludingburstmodeanddynamicSRon/offcontrolwhentransitioninginandoutofDiscontinuousCurrentMode(DCM)operation,ensuringZVSoperationisextendeddowntomuchlighterloads.
Inaddition,theUCC28950includessupportforpeakcurrentalongwithvoltagemodecontrol,programmableswitchingfrequencyupto1MHzandawidesetofprotectionfeaturesincludingcycle-by-cyclecurrentlimit,UVLOandthermalshutdown.
A90-degreephase-shiftedinterleavedsynchronizedoperationcanbeeasilyarrangedbetweentwoconverters.
TheUCC28950isavailableinTSSOP-24package.
ORDERINGINFORMATIONTEMPERATURERANGE,TA=PACKAGETAPEANDREELQTY.
PARTNUMBERTJ250UCC28950PW-40°Cto125°CPlastic24-pinTSSOP(PW)2000UCC28950PWRABSOLUTEMAXIMUMRATINGSoveroperatingfree-airtemperaturerange(unlessotherwisenoted)(1)(2)PARAMETERVALUEUNITInputsupplyvoltagerange,VDD(3)-0.
4to20.
0OUTA,OUTB,OUTC,OUTD,OUTE,OUTF-0.
4toVDD+0.
4InputsvoltagesonDELAB,DELCD,DELEF,SS/EN,DCM,TMIN,RT,SYNC,RSUM,EA+,EA-,-0.
4toVREF+COMP,CS,ADEL,ADELEF0.
4VOutputvoltageonVREF-0.
4to5.
6ESDrating,HBM2kESDrating,CDM500ContinuoustotalpowerdissipationSeedissipationratingtableOperatingvirtualjunctiontemperaturerange,TJ-40to150Operatingambienttemperaturerange,TA-40to125°CStoragetemperature,Tstg-65to150Leadtemperature(soldering,10sec.
)300(1)Stressesbeyondthoselistedunder"absolutemaximumratings"maycausepermanentdamagetothedevice.
Thesearestressratingsonly,andfunctionaloperationofthedeviceattheseoranyotherconditionsbeyondthoseindicatedunder"recommendedoperatingconditions"isnotimplied.
Exposuretoabsolute-maximum-ratedconditionsforextendedperiodsmayaffectdevicereliability.
(2)Thesedevicesaresensitivetoelectrostaticdischarge;followproperdevicehandlingprocedures.
(3)AllvoltagesarewithrespecttoGNDunlessotherwisenoted.
Currentsarepositiveinto,negativeoutofthespecifiedterminal.
SeePackagingSectionofthedatasheetforthermallimitationsandconsiderationsofpackages.
DISSIPATIONRATINGS(1)DERATINGPOWERRATINGFACTORRqJCRqJAPACKAGE(°C/W)(°C/W)ABOVETA=TA50%(somepublicationssuggestitmighthappenevenatD<50%).
Atlowdutycycleandlightload,theslopecompensationrampreducesnoisesensitivityofPeakCurrentModecontrol.
ToomuchadditionalslopecompensationrampreducesbenefitsofPCMcontrol.
Incaseofcycle-by-cyclecurrentlimit,theaveragecurrentlimitbecomeslowerandthismightreducethestartupcapabilitywiththelargeoutputcapacitance.
Theoptimalcompensationslopevariesdependingondutycycle,LOandLM.
Theslopecompensationisneededforthecontrolleroperatingatpeakcurrentmodecontrolorduringthecycle-by-cyclecurrentlimitatdutycycleabove50%.
PlacingaresistorfromRSUMpintogroundallowsthecontrollertooperateinpeakcurrentcontrolmode.
ConnectingRSUMpinthroughresistortoVREFswitchescontrollertothevoltagemodecontrolwiththeinternalPWMramp.
However,theresistorvaluestillprovidesCSsignalcompensationforcycle-by-cyclecurrentlimit.
Inotherwords,inVMC,theslopecompensationisappliedonlytocycle-by-cyclecomparator.
WhileinPCM,theslopecompensationappliedtobothPWMandcycle-by-cyclecurrentlimitcomparators.
TheoperationlogicofslopecompensationcircuitisshowninFigure11.
Figure11.
TheOperationLogicofSlopeCompensationCircuitTheslopeoftheadditionalramp,me,addedtoCSsignalbyplacingaresistorfromRSUMpintothegroundisdefinedbythefollowingEquation12.
(12)20SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010IftheresistorfromRSUMpinisconnectedtoVREFpin,thenthecontrolleroperatesinvoltagemodecontrol,stillhavingtheslopecompensationaddedtoCSsignalusedforcycle-by-cyclecurrentlimit.
InsuchacasetheslopeisdefinedbythefollowingEquation13.
(13)InEquation12andEquation13,theVREFisinvolts,RSUMisinkΩ,andmeisinV/s.
Theseareempiricalequationswithoutunitagreement.
Asanexample,substitutingVREF=5VandRSUM=40kΩ,yieldstheresult0.
125V/s.
TherelatedplotofmeasfunctionofRSUMisshowninFigure12.
BecauseVREF=5V,theplotsgeneratedfromEquation12andEquation13coincide.
Figure12.
SlopeoftheAddedRampOverResistorRSUMNOTETherecommendedresistorrangeforRSUMis10kΩto1MΩ.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback21ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
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comDynamicSRON/OFFControl(DCMMode)ThevoltageattheDCMpinprovidedbytheresistordividerRdcmhibetweenVREFpinandDCM,andRdcmfromDCMpintoGND,setsthepercentageof2-VcurrentlimitthresholdfortheCurrentSensepin,(CS).
IftheCSpinvoltagefallsbelowtheDCMpinthresholdvoltage,thenthecontrollerinitiatesthelightloadpowersavingmode,andshutsdownthesynchronousrectifiers,OUTEandOUTF.
IftheCSpinvoltageishigherthantheDCMpinthresholdvoltage,thenthecontrollerrunsinCCMmode.
ConnectingtheDCMpintoVREFmakesthecontrollerruninDCMmodeandshutsbothOutputsOUTEandOUTF.
ShortingtheDCMpintoGNDdisablestheDCMfeatureandthecontrollerrunsinCCMmodeunderallconditions.
Figure13.
DCMFunctionalBlockFigure14.
DutyCycleChangeOverLoadCurrentChange22SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010Thereisanominal20-Aswitchedcurrentsourceusedtocreatehysteresis.
ThecurrentsourceisactiveonlywhenthesystemisinDCMMode.
Otherwise,itisinactiveanddoesnotaffectthenodevoltage.
Therefore,whenbeinginDCMregion,theDCMthresholdisthevoltagedividerplusΔVexplainedinEquation14below.
WhenbeinginCCMregion,thethresholdisthevoltagesetbytheresistordivider.
WhenCSpinreachesthethresholdsetontheDCMpin,thesystemwaitstoseetwoconsecutivefallingedgePWMcyclesbeforeswitchingfromCCMtoDCMandvice-versa.
Themagnitudeofthehysteresisisafunctionoftheexternalresistordividerimpedance.
ThehysteresiscanbecalculatedusingthefollowingEquation14:(14)Figure15.
MovingfromDCMtoCCMModeFigure16.
MovingfromCCMtoDCMModeDCMmustbeusedinordertopreventreversecurrentintheoutputinductorwhichcouldcausethesynchronousFETStofail.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback23ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comCurrentSensing(CS)Thesignalfromcurrentsensepinisusedforcycle-by-cyclecurrentlimit,peak-currentmodecontrol,light-loadefficiencymanagementandsettingthedelaytimeforoutputsOUTA,OUTB,OUTC,OUTDanddelaytimeforoutputsOUTE,OUTF.
ConnectthecurrentsenseresistorRCSbetweenCSandGND.
Dependingonlayout,topreventapotentialelectricalnoiseinterference,itisrecommendedtoputasmallR-CfilterbetweenRCSresistorandCSpin.
Cycle-by-CycleCurrentLimitCurrentProtectionandHiccupModeThecycle-by-cyclecurrentlimitprovidespeakcurrentlimitingontheprimarysideoftheconverterwhentheloadcurrentexceedsitspredeterminedthreshold.
Forpeakcurrentmodecontrol,certainleadingedgeblankingtimeisneededtopreventthecontrollerfromfalsetrippingduetoswitchingnoise.
InordertosaveexternalRCfilterfortheblankingtime,aninternal30-nsfilteratCSinputisprovided.
ThetotalpropagationdelayTCSfromCSpintooutputsis100ns.
AnexternalRCfilterisstillneededifthepowerstagerequiresmoreblankingtime.
The2.
0-V±3%cycle-by-cyclecurrentlimitthresholdisoptimizedforefficientcurrenttransformerbasedsensing.
Thedurationwhenaconverteroperatesatcycle-by-cyclecurrentlimitdependsonthevalueofsoft-startcapacitorandhowseveretheovercurrentconditionis.
ThisisachievedbytheinternaldischargecurrentIDSEquation15andEquation16atSSpin.
(15)(16)Thesoft-startcapacitorvaluealsodeterminesthesocalledhiccupmodeoff-timeduration.
Thebehavioroftheconverterduringdifferentmodesofoperation,alongwithrelatedsoftstartcapacitorcharge/dischargecurrentsareshowninFigure17.
Figure17.
TimingDiagramofSoft-StartVoltageVSS24SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010Thelargestdischargecurrentof20Aiswhenthedutycycleisclosetozero.
Thiscurrentsetstheshortestoperationtimeduringthecycle-by-cyclecurrentlimitwhichisdefinedas:(17)(18)Thus,ifthesoft-startcapacitorCSS=100nFisselected,thentheTCL(on)timewillbe5ms.
TocalculatethehiccupofftimeTCL(off)beforetherestart,thefollowingEquation19orEquation20needstobeused:(19)(20)Withthesamesoftstartcapacitorvalue100nF,theofftimebeforetherestartisgoingtobe122ms.
Notice,thatiftheovercurrentconditionhappensbeforethesoftstartcapacitorvoltagereachesthe3.
7-Vthresholdduringstartup,thecontrollerlimitsthecurrentbutthesoftstartcapacitorcontinuestobecharged.
Assoonasthe3.
7-Vthresholdisreached,thesoft-startvoltageisquicklypulleduptothe4.
65-Vthresholdbyaninternal1-kΩRDS(on)switchandthecycle-by-cyclecurrentlimitdurationtimingstartsbydischargingthesoftstartcapacitor.
Dependingonspecificdesignrequirements,theusercanoverridedefaultparametersbyapplyingexternalchargeordischargecurrentstothesoftstartcapacitor.
Thewholecycle-by-cyclecurrentlimitandhiccupoperationisshowninFigure17.
Inthisexamplethecycle-by-cyclecurrentlimitlastsabout5msfollowedby122msofofftime.
Similartotheovercurrentcondition,thehiccupmodewiththerestartcanbeoverriddenbytheuserifapullupresistorisconnectedbetweentheSSandVREFpins.
Ifthepullupcurrentprovidedbytheresistorexceeds2.
5A,thenthecontrollerremainsinthelatchoffmode.
Inthiscase,anexternalsoft-startcapacitorvalueshouldbecalculatedwiththeadditionalpull-upcurrenttakenintoaccount.
Thelatchoffmodecanberesetexternallyifthesoft-startcapacitorisforciblydischargedbelow0.
55VortheVDDvoltageisloweredbelowtheUVLOthreshold.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback25ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comSynchronization(SYNC)TheUCC28950allowsflexibleconfigurationofconvertersoperatinginsynchronizedmodebyconnectingallSYNCpinstogetherandbyconfigurationofthecontrollersasmasterand/orslaves.
ThecontrollerconfiguredasMaster(resistorbetweenRTandVREF)providessynchronizationpulsesattheSYNCpinwiththefrequencyequalto2XtheconverterfrequencyFSW(nom)and0.
5dutycycle.
ThecontrollerconfiguredasaSlave(resistorbetweenRTandGNDand825-kΩresistorbetweenSS_ENpintoGND)doesnotgeneratethesynchronizationpulses.
TheSlavecontrollersynchronizesitsownclocktothefallingedgeofsynchronizationsignalthusoperating90°phaseshiftedversusthemasterconverter'sfrequencyFSW(nom).
BecausetheSlaveissynchronizedtothefallingedgeoftheSYNCpulses,theslaveoperatesat180delayedversusMaster'sCLKor90delayedversusoutputswitchingpulsesofMaster.
SuchoperationbetweenMasterandSlaveprovidesmaximuminputcapacitorandoutputcapacitorripplecancellationeffectifinputsandoutputsofconvertersaretiedtogether.
Toavoidsystemissuesduringthesynchronizedoperationoffewconvertersthefollowingconditionsshouldbetakencareof.
IfanyconverterisconfiguredaasaSlave,theSYNCfrequencymustbegreaterthanorequalto1.
8timestheconverterfrequency.
Slaveconverterdoesnotstartuntilatleastonesynchronizationpulsehasbeenreceived.
IfanyorallconvertersareconfiguredasSlaves,theneachconverteroperatesatitsownfrequencywithoutsynchronizationafterreceivingatleastonesynchronizationpulse.
Thus,Ifthereisaninterruptionofsynchronizationpulsesattheslaveconverter,thenthecontrollerusesitsowninternalclockpulsestomaintainoperationbasedontheRTvaluethatisconnectedtoGNDintheSlaveconverter.
InMastermode,SYNCpulsesstartafterSSpinpassesitsEnablethresholdwhichis0.
55V.
SlavestartsgeneratingSS/ENvoltageeventhoughsynchronizationpulseshavenotbeenreceived.
ItisrecommendedthattheSSontheMastercontrollerstartsbeforetheSSontheSlavecontroller;thereforeSS/ENpinonmasterconvertermustreachitsEnablethresholdvoltagebeforeSS/ENontheslaveconverterstartsforproperoperation.
Onthesamenote,it'srecommendedthatTMINresistorsonbothMasterandSlavearesetatthesamevalue.
Figure18.
SYNC_OUT(MasterMode)TimingDiagramFigure19.
SYNC_IN(SlaveMode)TimingDiagram26SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
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comSLUSA16A–MARCH2010–REVISEDJULY2010Outputs(OUTA,OUTB,OUTC,OUTD,OUTE,OUTF)AllMOSFETcontroloutputshave0.
2-Adrivecapability.
ThecontroloutputsareconfiguredasP-MOSandN-MOStotempoleswithtypicalRDS(on)20Ωand10Ωaccordingly.
Thecontroloutputsarecapableofcharging100-pFcapacitorwithin12nsanddischargewithin8ns.
TheamplitudeofoutputcontrolpulsesisequaltoVDD.
ControloutputsaredesignedtobeusedwithexternalgateMOSFET/IGBTdrivers.
Thedesignisoptimizedtopreventthelatchupofoutputsandverifiedbyextensivetests.
TheUCC28950hasoutputsOUTA,OUTBdrivingtheactiveleg,initiatingthedutycyclelegofpowerMOSFETsinphase-shiftedfullbridgepowerstage,andoutputsOUTC,OUTDdrivingthepassiveleg,completingthedutycycleleg,asitisshownintypicaltimingdiagraminFigure47.
OutputsOUTEandOUTFareoptimizedtodrivethesynchronousrectifierMOSFETs(Figure20).
Theseoutputshave200-mApeak-currentcapabilitiesandaredesignedtodriverelativelysmallcapacitiveloadslikeinputsofexternalMOSFETorIGBTdrivers.
Recommendedloadcapacitanceshouldnotexceed100pF.
TheamplitudeofoutputsignalisequaltoVDDvoltage.
ThecapacitorsCOSSshowninFigure20areinternalMOSFETcapacitancesthatmustbetakenintoaccountduringdesignproceduretoestimatezerovoltageconditionandswitchinglosses.
Figure20.
PowerStageCopyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback27ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
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comSupplyVoltage(VDD)Connectthispintobiassupplyfrom8Vto17Vrange.
Placehighquality,lowESRandESL,atleast1-FceramicbypasscapacitorCVDDfromthispintoGND.
Itisrecommendedtouse10-ΩresistorinseriestoVDDpintoformRCfilterwithCVDDcapacitor.
Ground(GND)Allsignalsarereferencedtothisnode.
Itisrecommendedtohaveaseparatequiteanalogplaneconnectedinoneplacetothepowerplane.
TheanalogplanecombinesthecomponentsrelatedtothepinsVREF,EA+,EA-,COMP,SS/EN,DELAB,DELCD,DELEF,TMIN,RT,RSUM.
ThepowerplanecombinesthecomponentsrelatedtothepinsDCM,ADELEF,ADEL,CS,SYNC,OUTF,OUTE,OUTD,OUTC,OUTB,OUTA,andVDD.
AnexampleoflayoutandgroundplanesconnectionisshowninFigure21.
Figure21.
LayoutRecommendationforAnalogandPowerPlanes28SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010TYPICALCHARACTERISTICSFigure22.
Figure23.
Figure24.
Figure25.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback29ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comTYPICALCHARACTERISTICS(continued)Figure26.
Figure27.
Figure28.
Figure29.
30SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010TYPICALCHARACTERISTICS(continued)Figure30.
Figure31.
Figure32.
Figure33.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback31ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comTYPICALCHARACTERISTICS(continued)Figure34.
Figure35.
Figure36.
Figure37.
32SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010TYPICALCHARACTERISTICS(continued)Figure38.
Figure39.
Figure40.
Figure41.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback33ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comTYPICALCHARACTERISTICS(continued)Figure42.
Figure43.
Figure44.
Figure45.
34SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010TYPICALCHARACTERISTICS(continued)Figure46.
Copyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback35ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comAPPLICATIONINFORMATIONUCC28950ApplicationDescriptionTheefficiencyimprovementofphase-shiftedfull-bridgeDC/DCconverterwithUCC28950isachievedbyusingthesynchronousrectificationtechnique,controlalgorithmprovidingZVSconditionovertheentireloadcurrentrange,accurateadaptivetimingofthecontrolsignalsbetweenprimaryandsecondaryFETsandspecialoperatingmodesatlightloadforthehighestefficiencyandpowersaving.
ThesimplifiedelectricaldiagramofthisconverterisshowninFigure47.
Thecontrollerdeviceislocatedonthesecondarysideofconverter,althoughitcouldbelocatedonprimarysideaswell.
ThelocationonsecondarysideallowseasypowersystemlevelcommunicationandbetterhandlingofsometransientconditionsthatrequirefastdirectcontrolofthesynchronousrectifierMOSFETs.
ThepowerstageincludesprimarysideMOSFETs,QA,QB,QC,QDandsecondarysidesynchronousrectifierMOSFETs,QEandQF.
Forexample,forthe12-Voutputconvertersinserverpowersuppliesuseofthecenter-tappedrectifierschemewithL-Coutputfilterisapopularchoice.
Tomaintainhighefficiencyatdifferentoutputpowerconditions,theconverteroperatesinnominalsynchronousrectificationmodeatmidandhighoutputpowerlevels,withtransitioningtothedioderectifiermodeatlightloadandfurtherfollowedbytheburstmode,astheoutputpowerbecomesevenlower.
Allthesetransitionsarebasedonthecurrentsensingontheprimarysideusingthecurrentsensetransformerinthisspecificcase.
Figure47.
MajorWaveformsofPhase-ShiftedConverter36SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
ti.
comSLUSA16A–MARCH2010–REVISEDJULY2010Majorwaveformsofthephase-shiftedconverterduringnominaloperationmodeareshowninFigure47.
UppersixwaveformsintheFigure47showtheoutputdrivesignalsofthecontroller.
Atnominalmode,theoutputsOUTEandOUTFoverlapduringthepartoftheswitchingcyclewhenthebothrectifierMOSFETsareconductingandthewindingsofpowertransformerareshorted.
Current,IPR,isthecurrentflowingthroughtheprimarywindingofpowertransformer.
Thebottomfourwaveformsshowthedrain-sourcevoltagesofrectifierMOSFETs,VDS_QEandVDS_QF,thevoltageattheoutputinductor,VLOUT,andthecurrentthroughtheoutputinductor,ILOUT.
PropertimingbetweentheprimaryswitchesandsynchronousrectifierMOSFETsiscriticaltoachievehighestefficiencyandreliableoperationinthismode.
ThecontrollerdeviceadjuststheturnOFFtimingofrectifierMOSFETsasfunctionofloadcurrenttoensuretheminimumconductiontimeandreverserecoverylossesoftheirinternalbodydiodes.
ZVSisanimportantfeatureofrelativelyhighinputvoltageconverterstoreduceswitchinglossesassociatedwiththeinternalparasiticcapacitancesofpowerswitchesandtransformers.
ThecontrollerensuresZVSconditionsovertheentireloadcurrentrangebyadjustingthedelaytimebetweentheprimaryMOSFETsswitchinginthesameleginaccordancetotheloadvariation.
ControlleralsolimitstheminimumON-timepulseappliedtothepowertransformeratlightload,allowingthestorageofsufficientenergyintheinductivecomponentsofpowerstagefortheZVStransition.
Assoonastheloadcurrentkeepsreducingfromthemidloadcurrentdowntono-loadcondition,thecontrollerselectsthemostefficientpowersavingmodebymovingtheconverterfromthenominaloperationmodetothediscontinuous-currentdiode-rectificationmodeand,eventually,atverylight-loadandatno-loadcondition,totheburstmode.
Thesemodesandrelatedoutputsignals,OUTE,OUTF,drivingtherectifierMOSFETs,areshowninFigure48.
Figure48.
MajorWaveformsDuringTransitionsBetweenDifferentOperatingModesCopyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback37ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
ti.
comItisnecessarytopreventthereversecurrentflowthroughthesynchronousrectifierMOSFETsandoutputinductoratthelightload,duringparalleloperationandatsometransientconditions.
Suchreversecurrentresultsincirculatingofsomeextraenergybetweentheinputvoltagesourceandtheloadand,therefore,causesincreasedlossesandreducesefficiency.
AnothernegativeeffectofsuchreversecurrentisthelossofZVScondition.
Thesuggestedcontrolalgorithmpreventsreversecurrentflow,stillmaintainingmostofthebenefitsofsynchronousrectificationbyswitchingoffthedrivesignalsofrectifierMOSFETsinapredeterminedway.
Atsomepre-determinedloadcurrentthreshold,thecontrollerdisablesoutputsOUTEandOUTFbybringingthemdowntozero.
SynchronousrectificationusingMOSFETsrequiressomeelectricalenergytodrivetheMOSFETs.
Thereisaconditionbelowsomelight-loadthresholdwhentheMOSFETdriverelatedlossesexceedthesavingprovidedbythesynchronousrectification.
Atsuchlightload,itisbesttodisablethedrivecircuitandusetheinternalbodydiodesofrectifierMOSFETs,orexternaldiodesinparallelwiththeMOSFETs,formoreefficientrectification.
Inmostpracticalcases,thedrivecircuitneedstobedisabledclosetoDCMmode.
Thismodeofoperationiscalleddiscontinuous-currentdiode-rectificationmode.
Atverylight-loadandno-loadcondition,thedutycycle,demandedbytheclosed-feedback-loopcontrolcircuitforoutputvoltageregulation,canbeverylow.
ThiscouldleadtothelossofZVSconditionandincreasedswitchinglosses.
ToavoidthelossofZVS,thecontrolcircuitlimitstheminimumON-timepulseappliedtothepowertransformerusingresistorfromTMINpintoGND.
Therefore,theonlywaytomaintainregulationatverylightloadandatno-loadconditionistoskipsomepulses.
Thecontrollerskipspulsesinacontrollablemannertoavoidsaturationofthepowertransformer.
Suchoperationiscalledburstmode.
InBurstModetherearealwaysanevennumberofpulsesappliedtothepowertransformerbeforetheskippingofftime.
Thus,thefluxinthecoreofthepowertransformeralwaysstartsfromthesamepointduringthestartofeveryburstofpulses.
VoltageLoopCompensationRecommendationForbestresultsinthevoltageloopitisrecommendedtouseType2orType3compensationnetwork(Figure49).
Atype2compensationnetworkdoesnotrequirepassivecomponentsCZ2andRZ2.
Type1compensationisnotversatileenoughforaphaseshiftedfullbridge.
WhenevaluatingtheCOMPforbestresultsitisrecommendedtoputa1-kΩresistorbetweenthescopeprobeandtheCOMPpinoftheUCC28950.
Figure49.
Type3CompensationEvaluation38SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950UCC28950www.
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comSLUSA16A–MARCH2010–REVISEDJULY2010ExperimentalResultsExampleThefollowingexperimentalresultsarebasedon660-Woutputpowerprototypeofphaseshiftedfull-bridgeDC/DCconverter.
Theinputvoltageis300Vto400Vandtheoutputis12V,55A.
TheprimaryMOSFETsareSPA11N60CFDandthesynchronousrectifierMOSFETsareFDP047AN08A0,twoinparallel.
ThemeasuredefficiencyoftheprototypeisshowninFigure50.
Figure50.
EfficiencyofthePrototypePhase-ShiftedConverter(VIN=300V,350Vand400V,VOUT=12V)Becauseofthepowersavingneedevenatverylightandno-loadconditions,carefuloptimizationofoperationatlightloadconditionisrequiredtosettheproperboundariesbetweendifferentoperationmodes.
TheresultofthisoptimizationisshowninFigure51.
Thisplotdemonstratesthepowersavingswhilemovingfromthesynchronousrectificationmodeabove1-Aloadcurrent,intothediscontinuouscurrentmodewiththedioderectificationbetween0.
3-Aand1-Aloadcurrent,andeventuallyintotheburstmodeoperationatloadcurrentbelow0.
3A.
Figure51.
PowerLossesofthePrototypeatLight-LoadandNo-LoadConditionsCopyright2010,TexasInstrumentsIncorporatedSubmitDocumentationFeedback39ProductFolderLink(s):UCC28950UCC28950SLUSA16A–MARCH2010–REVISEDJULY2010www.
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comREVISIONHISTORYChangesfromOriginal(March2010)toRevisionAPageChangedUCC28950TypicalApplicationDiagram1ChangedConverterswitchingfrequencyfrom1400kHzto1000kHz3ChangedFunctionalBlockDiagram8ChangedTypicalApplicationDiagram8AddedFigure515ChangedEquation16AddedTypicalApplicationDiagram16AddedalwaysdeliverevennumberofPowercyclestoPowertransformer.
18Deleteddelivereitheroneortwopowerdeliverycyclepulses.
IfcontrollerdeliversapowerdeliverycycleforOUTBandOUTC,thenitstops.
IfitstartsdeliveringtoOUTAandOUTD,thenitcontinueswithanotherpowerdeliverycycletoOUTBandOUTC,andthenitstops.
1840SubmitDocumentationFeedbackCopyright2010,TexasInstrumentsIncorporatedProductFolderLink(s):UCC28950PACKAGINGINFORMATIONOrderableDeviceStatus(1)PackageTypePackageDrawingPinsPackageQtyEcoPlan(2)Lead/BallFinishMSLPeakTemp(3)UCC28950PWACTIVETSSOPPW2460Green(RoHS&noSb/Br)CUNIPDAULevel-1-260C-UNLIMUCC28950PWRACTIVETSSOPPW242000Green(RoHS&noSb/Br)CUNIPDAULevel-1-260C-UNLIM(1)Themarketingstatusvaluesaredefinedasfollows:ACTIVE:Productdevicerecommendedfornewdesigns.
LIFEBUY:TIhasannouncedthatthedevicewillbediscontinued,andalifetime-buyperiodisineffect.
NRND:Notrecommendedfornewdesigns.
Deviceisinproductiontosupportexistingcustomers,butTIdoesnotrecommendusingthispartinanewdesign.
PREVIEW:Devicehasbeenannouncedbutisnotinproduction.
Samplesmayormaynotbeavailable.
OBSOLETE:TIhasdiscontinuedtheproductionofthedevice.
(2)EcoPlan-Theplannedeco-friendlyclassification:Pb-Free(RoHS),Pb-Free(RoHSExempt),orGreen(RoHS&noSb/Br)-pleasecheckhttp://www.
ti.
com/productcontentforthelatestavailabilityinformationandadditionalproductcontentdetails.
TBD:ThePb-Free/Greenconversionplanhasnotbeendefined.
Pb-Free(RoHS):TI'sterms"Lead-Free"or"Pb-Free"meansemiconductorproductsthatarecompatiblewiththecurrentRoHSrequirementsforall6substances,includingtherequirementthatleadnotexceed0.
1%byweightinhomogeneousmaterials.
Wheredesignedtobesolderedathightemperatures,TIPb-Freeproductsaresuitableforuseinspecifiedlead-freeprocesses.
Pb-Free(RoHSExempt):ThiscomponenthasaRoHSexemptionforeither1)lead-basedflip-chipsolderbumpsusedbetweenthedieandpackage,or2)lead-baseddieadhesiveusedbetweenthedieandleadframe.
ThecomponentisotherwiseconsideredPb-Free(RoHScompatible)asdefinedabove.
Green(RoHS&noSb/Br):TIdefines"Green"tomeanPb-Free(RoHScompatible),andfreeofBromine(Br)andAntimony(Sb)basedflameretardants(BrorSbdonotexceed0.
1%byweightinhomogeneousmaterial)(3)MSL,PeakTemp.
--TheMoistureSensitivityLevelratingaccordingtotheJEDECindustrystandardclassifications,andpeaksoldertemperature.
ImportantInformationandDisclaimer:TheinformationprovidedonthispagerepresentsTI'sknowledgeandbeliefasofthedatethatitisprovided.
TIbasesitsknowledgeandbeliefoninformationprovidedbythirdparties,andmakesnorepresentationorwarrantyastotheaccuracyofsuchinformation.
Effortsareunderwaytobetterintegrateinformationfromthirdparties.
TIhastakenandcontinuestotakereasonablestepstoproviderepresentativeandaccurateinformationbutmaynothaveconducteddestructivetestingorchemicalanalysisonincomingmaterialsandchemicals.
TIandTIsuppliersconsidercertaininformationtobeproprietary,andthusCASnumbersandotherlimitedinformationmaynotbeavailableforrelease.
InnoeventshallTI'sliabilityarisingoutofsuchinformationexceedthetotalpurchasepriceoftheTIpart(s)atissueinthisdocumentsoldbyTItoCustomeronanannualbasis.
PACKAGEOPTIONADDENDUMwww.
ti.
com14-Apr-2010Addendum-Page1TAPEANDREELINFORMATION*AlldimensionsarenominalDevicePackageTypePackageDrawingPinsSPQReelDiameter(mm)ReelWidthW1(mm)A0(mm)B0(mm)K0(mm)P1(mm)W(mm)Pin1QuadrantUCC28950PWRTSSOPPW242000330.
016.
46.
958.
31.
68.
016.
0Q1PACKAGEMATERIALSINFORMATIONwww.
ti.
com20-Jul-2010PackMaterials-Page1*AlldimensionsarenominalDevicePackageTypePackageDrawingPinsSPQLength(mm)Width(mm)Height(mm)UCC28950PWRTSSOPPW242000346.
0346.
033.
0PACKAGEMATERIALSINFORMATIONwww.
ti.
com20-Jul-2010PackMaterials-Page2MECHANICALDATAMTSS001C–JANUARY1995–REVISEDFEBRUARY1999POSTOFFICEBOX655303DALLAS,TEXAS75265PW(R-PDSO-G**)PLASTICSMALL-OUTLINEPACKAGE14PINSSHOWN0,65M0,100,100,250,500,750,15NOMGagePlane289,809,60247,907,7020166,606,404040064/F01/970,306,606,2080,194,304,5070,1514A11,20MAX145,104,9083,102,90AMAXAMINDIMPINS**0,054,905,10SeatingPlane0°–8°NOTES:A.
Alllineardimensionsareinmillimeters.
B.
Thisdrawingissubjecttochangewithoutnotice.
C.
Bodydimensionsdonotincludemoldflashorprotrusionnottoexceed0,15.
D.
FallswithinJEDECMO-153IMPORTANTNOTICETexasInstrumentsIncorporatedanditssubsidiaries(TI)reservetherighttomakecorrections,modifications,enhancements,improvements,andotherchangestoitsproductsandservicesatanytimeandtodiscontinueanyproductorservicewithoutnotice.
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