Under the hood of low-voltage DC DC converters.pdf

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1、TitleSlideTopic5UndertheHoodofLow-VoltageDC/DCConvertersBrianLynchKurtHesseOutline©SynchronousBuckReview©Designaconverter¢Controller¢FETs¢Inductor¢Capacitors¢FeedbackDesign©Results©ConclusionSynchronousBuckSynchronousSWNodeRectifierAveragingCircuitSwitchOutputDCInputZVCCSRZCOMP+PWMZGNDControlCircuit

2、SynchronousBuckWaveformsContinuousConductionModePWMSwitchSynchronousRectifierSwitchCurrentGNDSynchronousRectifierCurrentGNDVinSwitchAverageVoutNodeGNDInductorAverageIoutCurrentGNDt2t6t7t3t5t1t4t0t8TsSynchronousRectifierFETCurrentPWMSwitchSynchronousRectifierTotalSynchronousRectifierCurrentGNDDiodeCu

3、rrentGNDChannelCurrentGNDVinSwitchAverageVoutNodeGNDt2t6t7t3t5t1t4t0t8TsSynchronousBuckWaveformsDiscontinuousConductionModePWMSynchronousRectifierSwitchGNDCurrentSynchronousRectifierGNDCurrentSwtchNodeAverageVoutGNDInductorGNDCurrentt0t2t4t6t1t3t5BasicRelationshipsContinuousConductionMode(CCM)tonVou

4、tD==TsVin(Vin−Vout)⋅D⋅Ts∆Iout=LDiscontinuousConductionMode(DCM)2L⋅IOVoutD=⋅TsV2−V⋅VininoutUnderTheHoodDesignExampleDesignGoals©InputVoltage:3.3V©OutputVoltage:1.2V©OutputCurrent:10A©Optimizeforpowerdensity¢Lowpowerdissipation¢SmallsizeControllerSelection©TPS40003¢600kHz¢PredictiveGateDriveTM¢Smallsi

5、ze:10-pinMSOP¢2Amppeakon-boarddrivers¢CCMoperationPredictiveGateDrive™VINZeroVVDGNDChannelConductionBodyDiodeConduction-VDFixedDelayAdaptiveDelayPredictiveDelayInductorConsiderations©BenefitsoflowLvalues¢LowerDCR¢HigherIsat¢Higherdi/dt®Transientresponseimproves®Lessoutputcapacitancerequiredforgivent

6、ransientperformance©BenefitsofhighLvalues¢Lowerripplecurrent®LowerAClosses(skineffect,hysteresis)®LowerRMScurrentinFETs®LowerRMScapacitorcurrent(mainlyoutput)®Continuousinductorcurrentoverbroaderloadrange®LessCrequiredforequivalentoutputrippleGeneralInductorGuidelines©Sizefor∆Itobe10%to30%offullload

7、currentL©Windinglossesusuallydominate2PL=IL⋅RLAVGRMS2∆IL2ppwhereIL=I+RMSout12InductorandFETs1.251.201.15Loss(W)wero1.10PR1.05andS1.00chitw0.95edSizal0.900.85Norm0.800102030405060708090100I/I(%)RIPPLEL