MOSFET Basic

1MOSFETBasics2Cross-sectionofaLaterallyDiffusedMOSFET(LDMOS)structureLateralMOSFET3Cross-sectionoftwoverticalMOSFETstructures:VMOSandUMOSVMOSFETandUMOSFET4AMOSFETdrivenbyagatevoltageOperationofMOSFETN+P+N+P-substrateVg+-0.1VDepletioncapacitanceFormationofdepletionregionFormationofinversionlayer(Vg++)N+P+N+P-substrateVg+-0.1V------------N+P+N+P-substrateVg+++-0.1V-------------------------N+P+N+P-substrateVg+++-0.1VCoxCdep5Drain-sourceonResistance(RDS(ON))RDS(on)=RN++RCH+RA+Rj+RD+RS6ContinuousDrainCurrent(ID)TheIDratingisdeterminedbytheheatremovalabilityofthedevice.IncreasingpermissibleIDasTCdecreases.RJC:maximumjunction–to–casethermalresistanceTJMAX:maximumjunctiontemperatureTC:casetemperature7ActualMOSFETRDS(ON)ForhighsideMOSFET,theturnonVgs=Vg-Vs=11-5=6VRefertoabovecurve,Vgs6v=6V@20AFDB7030BL’sRds(on)@Vgs6visRdson_Vgs6v=1.1xRdson_Vgs10=1.1x8.5m=9.35m8ActualMOSFETRDS(ON)(II)Assumetheoperatingjunctiontemperatureat100ºCforFDB7030BL,whichis1.3timesRds(on)ofthatat25ºCCombinepreviouscalculation:Rds(on)ofFDB7030BL@Vgs=6V,Tj=100ºC,ID=20Ais:1.3X9.35m=12.16m9MOSFET’sParasiticCapacitance10CapacitanceTests(Equipmentused:BenchpowerSuppliesandAgilentHP4194AorBoontonMeter72B)0.1F1000pF7.6mH30FVDSHILODUTCISSTestCircuit0.1F1000pF7.6mH30FVDSHILODUTCISSTestCircuitMechanicsoftheTestsa.)TheHIandLOterminals,asshownoneachtestsetupabove,aretobeconnectedtotheHiandLoterminalsoftheCapacitancemeter.YoucanuseeithertheBoontonorAgilentcapacitancemeters.b.)TheVdsisturn-ongiventhespecificforcingconditionasdefinedinthespecs.c.)Thecapacitancevalueissimplytakingtheresultsasdisplayedonthemeterbeingused.CissMeasure110.1F2mHVDSHILODUTCRSSTestCircuit0.1F2mHVDSHILODUTCRSSTestCircuitMechanicsoftheTestsa.)TheHIandLOterminals,asshownoneachtestsetupabove,aretobeconnectedtotheHiandLoterminalsoftheCapacitancemeter.YoucanuseeithertheBoontonorAgilentcapacitancemeters.b.)TheVdsisturn-ongiventhespecificforcingconditionasdefinedinthespecs.c.)Thecapacitancevalueissimplytakingtheresultsasdisplayedonthemeterbeingused.CrssMeasure120.1F2mHVDSHILODUTCOSSTestCircuit0.1F2mHVDSHILODUTCOSSTestCircuitMechanicsoftheTestsa.)TheHIandLOterminals,asshownoneachtestsetupabove,aretobeconnectedtotheHiandLoterminalsoftheCapacitancemeter.YoucanuseeithertheBoontonorAgilentcapacitancemeters.b.)TheVdsisturn-ongiventhespecificforcingconditionasdefinedinthespecs.c.)Thecapacitancevalueissimplytakingtheresultsasdisplayedonthemeterbeingused.CossMeasure13VDSIGSW1DUTCGSCGDIDBasicGateChargeTestCircuitVDSVTHIDDrainVoltageDrainCurrentt0t1t2t3t4QGSQGDVGtimeGateChargeWaveformsQGVDSIGSW1DUTCGSCGDIDBasicGateChargeTestCircuitVDSIGSW1DUTCGSCGDIDVDSIGSW1DUTCGSCGDIDBasicGateChargeTestCircuitVDSVTHIDDrainVoltageDrainCurrentt0t1t2t3t4QGSQGDVGtimeGateChargeWaveformsQGVDSVTHIDDrainVoltageDrainCurrentt0t1t2t3t4QGSQGDVGtimeGateChargeWaveformsQGGateChargeTest(Equipmentused:BenchPowersupplies,Oscilloscope,andHome-brewedcircuit)MechanicsoftheTest:3.a.)TheDUTistestedgiventheVds,andIdforcedconditions.3.b.)TheIgisusuallyappliedfromaconstantcurrentsourceasshowninthesimplifiedlayout.TheIgisusuallyselectedateither1mAor100uAdependingonthediesizeoftheDUT.3.c.)TheIdisalsoappliedbasedontheprogrammedIdconditions.3.d.)TheQgs,Qgd,andtotalQgaremeasuredbasedonthegraphstotherightshowingthetime.Thecharge,Q,issimplytakenfromtheequation:q=ixt(Igcurrentxtime).3.e.)SW1isusedtodischargetheGatechargeaftereverytestisconducted.GateChargeMeasure14Ohmicregion:ConstantResistanceRegion.Saturationregion:ConstantCurrentRegion.Cut-offregion:ItiscalledCut-OffRegion.Ohmic[VGS–VGS(th)=VDS]ActiveVGS5VGS4VGS3VGS2VGS1CutOffVDSiDVGS5VGS4VGS3VGS2VGS1VGSVGS(TH)OutputCharacteristics0BVDSSMOSFETOutputCharacteristics15ThegraphofVgs,Ig,VdsandIdwhenMOSFETturnon16RgIoCgd+-VgRgIoCgdRds(on)+-Vgequivalentcircuitofperiodt1–t2equivalentcircuitofperiodt0–t1equivalentcircuitofperiodt2–t3equivalentcircuitofperiodt3–t4CgdCgsCdDFIoRg+-VgVdRgCgsCdDFCgdIoVg-+VdVdVdEquivalentcircuitsoftheMOSFETturn–on17HighSideSwitchingLossHighsideConductionLossMOSFETPowerDissipationforDC-DCConverterPsw12Iout12ILrippleVintffsw12Iout12ILrippleVintrfswPsw12IoutVintrtffsw14VinfswILrippletftrPconIout2RDSON()D18LowsideConductionLossfsw:switchingfrequencytr:switchingrisetimetf:switchingfalltimeP:phaseNo.(interleaveno.)ILripple:inductorcurrent(pk-pk)D:dutycycleVf:SchottkyorbodydiodeforwardVoltageHighsidePowerloss=Psw+PconLowsidePowerloss=Pcon+Psw(ignoredifsmallenough)Psw12IoutVftrtffsw14VffswILrippletftrLowSideSwitchingLossPconIout2RDSON()1D()19ThePathoftheThermalDischargeattheChipJunctionRJCRCSRSAPD20D2PAK(TO-263)PowerMOSFETTypicalThermalData21Rjav.s.CopperMountingPADArea22TheMOSFETverticalstructureshowingtheparasiticBJTanddiode23EquivalentCircuitofPowerMOSFETShowingTwoPossibleMechanismsfordv/dtInducedTurn-on24CrossConductionISSRSSCCdTdVtPulseHeighTOP(Q1)CONTROLBOTTOM(Q2)CONTROLQ2DrainVoltageVGIVthVinGQ1Q2ISSCRSSCG1RPWMOutputDriverVGI25Fig.1–UISTestCircuitD.U.TVDD+-SW1D1LVGSFig.1–UISTestCircuitD.U.TV