升压MT3608

同步异步升压芯片MT3608FEATURES集成80mΩ功率MOSFET2V到24V输入电压1.2MHz固定开关频率内部4A开关电流限制可调输出电压内部补偿高达28V输出电压自动脉冲调频模式,光负荷高达97%6针SOT23-6封装的效率APPLICATIONS•Battery-PoweredEquipment•Set-TopBoxed•LCDBaisSupply•DSLandCableModemsandRouters•NetworkingcardspoweredfromPCIorPCIexpressslotsTYPICALAPPLICATIONFigure1.BasicApplicationCircuit3-HighEfficiency1.2MHz2A步进变流器GENERALDESCRIPTIONMT3608是一个恒定频率,6针SOT23电流模式的升压转换器,用于小型,低功耗应用。MT3608开关在1.2MHz和允许使用小,低成本电容器和电感2mm或更低的高度。内部软启动导致小浪涌电流,延长电池寿命。MT3608的特点是在光负载下自动切换到脉冲调频模式。MT3608包括欠压锁定、电流限制和热过载保护,以防输出过载时损坏。MT3608在一个小的6针SOT-23包中可用。EfficiencyIout(mA)Figure2.EfficiencyCurve1Efficiency(%)MT3608同步异步升压芯片2SOT23-5(MT3540)SOT23-6(MT3608)162534ABSOLUTEMAXIMUMRATINGSIN,ENvoltages………..….……-0.3Vto26VOperatingTemperature…....-40°Cto+85°CFBVoltages................................-0.3Vto6VJunctionTemperature………………...160°CSWVoltage……………………..-0.3Vto30VStorageTemperatureRange-65°Cto150°CPeakSWSinkandSourceCurrent………4ALeadTemperature(Soldering,10s)...+300°CPACKAGE/ORDERINFORMATIONSWNCGNDINFBENPINDESCRIPTIONPINNAMEFUNCTION1SWPowerSwitchOutput.SWisthedrainoftheinternalMOSFETswitch.ConnectthepowerinductorandoutputrectifiertoSW.SWcanswingbetweenGNDand28V.2GNDGroundPin3FBFeedbackInput.TheFBvoltageis0.6V.ConnectaresistordividertoFB.4ENRegulatorOn/OffControlInput.AhighinputatENturnsontheconverter,andalowinputturnsitoff.Whennotused,connectENtotheinputsupplyforautomaticstartup.5INInputSupplyPin.Mustbelocallybypassed.6NCNCMT3608同步异步升压芯片3ELECTRICALCHARACTERISTICS(VIN=VEN=5V,TA=25°C,unlessotherwisenoted.)ParameterConditionsMINTYPMAXunitOperatingInputVoltage224VUnderVoltageLockout1.98VUnderVoltageLockoutHysteresis100mVCurrent(Shutdown)VEN=0V0.11µAQuiescentCurrent(PFM)VFB=0.7V，Noswitch100200µAQuiescentCurrent(PWM)VFB=0.5V，switch1.62.2mASwitchingFrequency1.2MHzMaximumDutyCycleVFB=0V90%ENInputHighVoltage1.5VENInputLowVoltage0.4VFBVoltage0.5880.60.612VFBInputBiasCurrentVFB=0.6V-50-10nASWOnResistance(1)80150mΩSWCurrentLimit(1)VIN=5V,Dutycycle=50%4ASWLeakageVSW=20V1μAThermalShutdown155℃Note:1)Guaranteedbydesign,nottested.MT3608同步异步升压芯片4OPERATIONTheMT3608usesafixedfrequency,peakcurrentmodeboostregulatorarchitecturetoregulatevoltageatthefeedbackpin.TheoperationoftheMT3608canbeunderstoodbyreferringtotheblockdiagramofFigure3.AtthestartofeachoscillatorcycletheMOSFETisturnedonthroughthecontrolcircuitry.Topreventsub-harmonicoscillationsatdutycyclesgreaterthan50percent,astabilizingrampisaddedtotheoutputofthecurrentsenseamplifierandtheresultisfedintothenegativeinputofthePWMcomparator.WhenthisvoltageequalsTheoutputvoltageoftheerroramplifierthepowerMOSFETisturnedoff.Thevoltageattheoutputoftheerroramplifierisanamplifiedversionofthedifferencebetweenthe0.6Vbandgapreferencevoltageandthefeedbackvoltage.Inthiswaythepeakcurrentlevelkeepstheoutputinregulation.Ifthefeedbackvoltagestartstodrop,theoutputoftheerroramplifierincreases.TheseresultsinmorecurrenttoflowthroughthepowerMOSFET,thusincreasingthepowerdeliveredtotheoutput.TheMT3608hasinternalsoftstarttolimittheamountofinputcurrentatstartupandtoalsolimittheamountofovershootontheoutput.Figure3.FunctionalBlockDiagramMT3608同步异步升压芯片5TYPICALOPERATINGCHARACTERISTICSEfficiencyCurveEfficiencyCurveIout(mA)lineRegulationIout(mA)LoadregualationVin(V)FreqVSVinIout(mA)EfficiencyVSVinVout(V)EfficiencyCurrentlimit(A)Vout(V)MT3608同步异步升压芯片6APPLICATIONINFORMATIONSettingtheOutputVoltageTheinternalreferenceVREFis0.6V(Typical).Theoutputvoltageisdividedbyaresistordivider,R1andR2totheFBpin.TheoutputvoltageisgivenbyRLayoutConsiderationForbestperformanceoftheMT3608,thefollowingguidelinesmustbestrictlyfollowed.InputandOutputcapacitorsshouldbeplacedclosetotheICandconnectedtogroundplaneVOUTVREF(11)Rtoreducenoisecoupling.2InductorSelectionTherecommendedvaluesofinductorare4.7to22μH.Smallsizeandbetterefficiencyarethemajorconcernsforportabledevice,suchasMT3608usedformobilephone.Theinductorshouldhavelowcorelossat1.2MHzandlowDCRforbetterefficiency.Toavoidinductorsaturationcurrentratingshouldbeconsidered.CapacitorSelectionInputandoutputceramiccapacitorsof22μFarerecommendedforMT3608applications.Forbettervoltagefiltering,ceramiccapacitorswithlowESRarerecommended.X5RandX7Rtypesaresuitablebecauseoftheirwidervoltageandtemperatureranges.DiodeSelectionSchottkydiodeisagoodchoiceforMT3608becauseofitslowforwardvoltagedropandfastreversesrecovery.UsingSchottkydiodecangetbetterefficiency.ThehighspeedrectificationisalsoagoodcharacteristicofSchottkydiodeforhighswitchingfrequency.Currentratingofthediodemustmeettherootmeansquareofthepeakcurrentandoutputaveragecurrentmultiplicationasfollowing:ID(RMS)Thediode’sreversebreakdownvoltageshouldbelargerthantheoutputvoltage.TheGNDshouldbeconnectedtoastronggroundplaneforheatsinkingandnoiseprotection.Keepthemaincurrenttracesaspossibleasshortandwide.SWnodeofDC-DCconverteriswithhighfrequencyvoltageswing.Itshouldbekeptatasmallarea.PlacethefeedbackcomponentsascloseaspossibletotheICandkeepawayfromthenoisydevices.IOUTIPEAKMT3608同步异步升压芯片PACKAGEDESCRIPTIONTOPVIEWRECOMMENDEDLANDPATTERNFRONTVIEWSIDEVIEWDETAIL“A”Figure4