L6699-无PFC应用

June2015DocID026993Rev31/2626AN4599ApplicationnoteSTEVAL-ISA132V124V300WpeakpowerresonantconverterbyRiccardoTosoniIntroductionThisapplicationnotedescribesthefeaturesoftheSTEVAL-ISA132V1evaluationboardat24V,300Wpeakpowerconversion.Thearchitectureisbasedonasingle-stageLLCresonantconverterwithoutPFCusingthenewL6699resonantcontroller.TheL6699integratessomeveryinnovativefunctionssuchasself-adjustingadaptivedeadtime,anti-capacitivemodeprotectionandaproprietarysafe-startprocedurewhichpreventshardswitchingatstart-up.Thankstothechipsetused,themainfeaturesofthispowersupplyare:–veryhighefficiencyunderhigh-loadandlow-loadconditions–safestartupproceduretoavoidhardswitching–hardswitchingpreventionunderoverloadandlow-loadconditions–burstmodeunderlow-loadconditionswithsmoothrestarttopreventaudiblenoise–thedemoboardcandelivermorethan300WpeakpowerforalimitedtimethankstotheNTCthermalprotectionpositionedneartheoutputdiodes.–continuouspowerat30°Cambienttemperatureis170W.–theMOSFETanddiodepowerdevicesareinD²PAKpackagesFigure1.STEVAL-ISA132V1300WpeakpowerSMPevaluationboard:•inputmainsrange:from190to264VAC-frequency50Hz•outputvoltage:24V5%•no-loadconsumption:0.6W•efficiency@230Vac92%•EMI:WithinEN55022Class-Blimitsconductedprecompliance•safety:MeetsEN60950-1•dimensions:90x90mm,50mmcomponentmaximumheight•weight220grThecircuitconsistsofasinglestageLLCresonantconverter.TheMOSFETanddiodepowercomponentsareinD²PAKpackages.TheL6699integratesallthefunctionsnecessarytocontroltheresonantconverterwitha50%fixeddutycycleandworkingwithvariablefrequency.CircuitdescriptionAN45994/26DocID026993Rev32Circuitdescription2.1Start-upsequenceD12,D4,R7,C13inFigure13formthestart-upcircuit.WhentheVCCvoltagereachesL6699VCCon,thesystembeginsthestart-upsequenceandchangestheswitchingfrequencyfromfstarttotheoperativefrequency.2.2OscillatorsettingFigure2.Oscillator'sinternalblockdiagramTheoscillatorisprogrammedexternallybymeansofacapacitorconnectedfrompin3(CF)togroundthatisalternatelychargedanddischargedbythecurrentdefinedwiththenetworkconnectedtopin4(RFmin).Thepinprovidesanaccurate2Vreferencewithapproximately2mAsourcecapability;thehigherthecurrentsourcedbythepin,thehighertheoscillatorfrequency.TheFigure2blockdiagramshowsasimplifiedinternalcircuitexplainingtheoperation.Table1.RecommendedvaluesforCFasafunctionofthestart-upfrequencyfstartfstart[kHz]CF[pF]fstart[kHz]CF[pF]150680230-240180160560250150170470260120180390270100190-200330280822102702906821022030056$0Y/95)PLQ&)64599&),5ā.0ā,5.0ā,55)PLQ5)PD[566&66.0ā,5DocID026993Rev35/26AN4599Circuitdescription26Proceduretosetoscillatorcomponents:•nominatethestartfrequency(donotexceed300kHzfstart)•findthecorrespondingvalueofCFinTable1•withachosenfstartof156kHz,thecorrespondingCFis560pFinTable1•choosetheminimumfrequencyanddetermineRFminusingtheequation:Equation1ThechosenFminis49.6kHz,CFis560pFandthusRFmin=12kΩDetermineRSSusingequation:Equation2ForthechosenFstartof156kHz,CF=560pF,RFmin=12kΩandconsequentlyRSS=5.6kΩVerifythefollowingrelationships:Equation3ChooseFmaxanddetermineRFmaxusingtheformula:Equation4ForachosenFmaxof150kHz,RFmax=2kΩCalculatetheCSSusingtheformulaCSS=3*0.001/RSSIntheapplication,itmaybenecessarytoincreasethisvaluetooptimizestart-upprocedurebyminimizingtheinrushcurrentandchargingcurrentoftheoutputcapacitor.GoodperformanceisachievedwithCSS=4.7μF.CircuitdescriptionAN45996/26DocID026993Rev3WithreferencetotheschematicinFigure13:•RFmin=R18=12kΩ•RFmax=R19=3.3kΩ•RSS=R15=5.6kΩ•CF=C22=560pF•CSS=C26=4.7μF2.3BurstmodeoperationatnoloadorverylightloadToreducetheaverageswitchingfrequency,theL6699canoperateinburstmodewithaseriesofafewswitchingcyclesinbetweenrelativelylongidleperiodswithbothMOSFETsintheoffstate.Theresultingaveragevalueoftheresidualmagnetizingcurrentandc