Ringing Reduction Techniques for印制技术

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1、ApplicationReportSLPA010–November2011RingingReductionTechniquesforTMNexFETHighPerformanceMOSFETsABSTRACTTMThedesignofswitchingconverterswithhighperformanceMOSFET’ssuchasthosefoundintheNexFETproductlinerequirespecialattentiontodetailtomaximizetheeffectiveness

2、ofthedevicesandoptimizetheoverallperformanceoftheswitchingfunction.Considerationofthechallengesofworkingwithultra-fastpowerdevicesearlyinthedesignprocesswillensurethehighestperforming,mostreliablefinalproduct.InthisApplicationNote,thePowerStageofthetypicalNo

3、n-IsolatedSynchronousBuckConverter(seeFigure1)willbeusedasareferencefordiscussingpracticaldesignconsiderationsformaximizingtheperformanceandlifetimeofNexFETproducts.ThemostcommonproblemencounteredinthisscenarioisparasiticVoltageRingingsuperimposedontherising

4、edgeoftheSwitchNode.ThisApplicationNotewilldiscussthesourceoftheswitchnoderinging,measurementtechniquestoaccuratelycharacterizethisringing,andmethodsforminimizingtheeffectwhilemaintainingexcellentsystemperformance.BackgoundFigure1showstheschematicofatypicals

5、ynchronousbuckconverter.Astheperformanceofpowerdevicesisimproved,thecontrolFEThastheabilitytoswitchvoltagesatratesgreaterthan10kV/µs.However,thefastswitchingfacesacommonchallengeofdealingwithswitchingnoise.InparticularwhentheControlFETturnsonandtheSyncFETiso

6、ff,theloopinductor,theloopresistorandtheoutputcapacitorofthesyncFETformaseriesRLCloopandwillresonateataresonantfrequency.Thisresonancewillresultinvoltageovershootandringingattheswitchnode.InputCISupplyDriverControlPWMFETLOSwitchNodeCOILLoadDriverSyncFETFigur

7、e1.DefinitionofPowerStageComponentsTounderstandthesourceofthisringing,itisusefultomakeadetailedexaminationoftheswitchingtransient.AssumetheControlFETisoff,theSyncFETison,allvoltagetransientshavesettled,butILcontinuestoflow(slewingataconstantrate)(seeStage1in

8、Figure2).DuringStage2,theSyncFETisturnedoffandashortdeadtimeisimposedtopreventshoot-throughbeforetheControlFETisturnedon.DuringthedeadtimetheinductorcurrentforcesthebodydiodeoftheSyncFETtoturnon