sx1308-B628-dc-dc

HighEfficiency1.2MHz2AStepUpConverterFEATURES•Integrated80mΩPowerMOSFET•2Vto24VInputVoltage•1.2MHzFixedSwitchingFrequency•Internal4ASwitchCurrentLimit•AdjustableOutputVoltage•InternalCompensation•Upto28VOutputVoltage•AutomaticPulseFrequencyModulationModeatLightLoads•upto96%Efficiency•Availableina6-PinSOT23-6PackageAPPLICATIONS•Battery-PoweredEquipment•Set-TopBoxed•LCDBaisSupply•DSLandCableModemsandRouters•NetworkingcardspoweredfromPCIorPCIexpressslotsTYPICALAPPLICATIONFigure1.BasicApplicationCircuitTheSX1308isaconstantfrequency,6-pinSOT23currentmodestep-upconverterintendedforsmall,lowpowerapplications.TheSX1308switchesat1.2MHzandallowstheuseoftiny,lowcostcapacitorsandinductors2mmorlessinheight.Internalsoft-startresultsinsmallinrushcurrentandextendsbatterylife.TheSX1308featuresautomaticshiftingtopulsefrequencymodulationmodeatlightloads.TheSX1308includesunder-voltagelockout,currentlimiting,andthermaloverloadprotectiontopreventdamageintheeventofanoutputoverload.TheSX1308isavailableinasmall6-pinSOT-23package.EfficiencyIout(mA)Figure2.EfficiencyCurveEfficiency(%)GENERALDESCRIPTION85T85TSX13081Copyright©2010bySuosemiCorporationIN,ENvoltages………..….……-0.3Vto26VOperatingTemperature…....-40°Cto+85°CFBVoltages................................-0.3Vto6VJunctionTemperature………………...160°CSWVoltage……………………..-0.3Vto30VStorageTemperatureRange-65°Cto150°CPeakSWSinkandSourceCurrent………4ALeadTemperature(Soldering,10s)...+300°CPACKAGE/ORDERINFORMATION31246SOT23-5INGNDFBSWEN(MT3540)5NCPINDESCRIPTIONPINNAMEFUNCTION1SWPowerSwitchOutput.SWisthedrainoftheinternalMOSFETswitch.ConnectthepowerinductorandoutputrectifiertoSW.SWcanswingbetweenGNDand28V.2GNDGroundPin3FBFeedbackInput.TheFBvoltageis0.6V.ConnectaresistordividertoFB.4ENRegulatorOn/OffControlInput.AhighinputatENturnsontheconverter,andalowinputturnsitoff.Whennotused,connectENtotheinputsupplyforautomaticstartup.5INInputSupplyPin.Mustbelocallybypassed.6NCNCABSOLUTEMAXIMUMRATINGSSOT23-6(SX1308)SX13082Copyright©2010bySuosemiCorporationELECTRICALCHARACTERISTICS(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.SX13083Copyright©2010bySuosemiCorporationTheSX1308usesafixedfrequency,peakcurrentmodeboostregulatorarchitecturetoregulatevoltageatthefeedbackpin.TheoperationoftheSX1308canbeunderstoodbyreferringtotheblockdiagramofFigure3.AtthestartofeachoscillatorcycletheMOSFETisturnedonthroughthecontrolcircuitry.Topreventsub-harmonicoscillationsatdutycyclesgreaterthan50percent,astabilizingrampisaddedtotheoutputofthecurrentsenseamplifierandtheresultisfedintothenegativeinputofthePWMcomparator.WhenthisvoltageequalsTheoutputvoltageoftheerroramplifierthepowerMOSFETisturnedoff.Thevoltageattheoutputoftheerroramplifierisanamplifiedversionofthedifferencebetweenthe0.6Vbandgapreferencevoltageandthefeedbackvoltage.Inthiswaythepeakcurrentlevelkeepstheoutputinregulation.Ifthefeedbackvoltagestartstodrop,theoutputoftheerroramplifierincreases.TheseresultsinmorecurrenttoflowthroughthepowerMOSFET,thusincreasingthepowerdeliveredtotheoutput.TheSX1308hasinternalsoftstarttolimittheamountofinputcurrentatstartupandtoalsolimittheamountofovershootontheoutput.Figure3.FunctionalBlockDiagramOPERATIONSX13084Copyright©2010bySuosemiCorporationTYPICALOPERATINGCHARACTERISTICSEfficiencyCurveIout(mA)lineRegulationVin(V)FreqVSVinEfficiencyCurveIout(mA)LoadregualationIout(mA)EfficiencyVSVinEfficiencyVout(V)Currentlimit(A)Vout(V)SX13085Copyright©2010bySuosemiCorporationSettingtheOutputVoltageTheinternalreferenceVREFis0.6V(Typical).Theoutputvoltageisdividedbyaresistordivider,R1andR2totheFBpin.Theoutputvoltageisgivenby)1(21RRVVREFOUT+×=InductorSelectionTherecommendedvaluesofinductorare4.7to22μH.Smallsizeandbetterefficiencyarethemajorconcernsforportabledevice,suchasSX1308usedformobilephone.Theinductorshouldhavelowcorelossat1.2MHzandlowDCRforbetterefficiency.Toavoidinductorsaturationcurrentratingshouldbeconsidered.CapacitorSelectionInputandoutputceramiccapacitorsof22μFarerecommendedforSX1308applications.Forbettervoltagefiltering,ceramiccapacitorswithlowESRarerecommended.X5RandX7Rtypesaresuitablebecauseoftheirwidervoltageandtemperatureranges.DiodeSelectionSchottkydiodeisagoodchoiceforSX1308becauseofitslowforwardvoltagedropandfastreversesrecovery.UsingSchottkydiodecangetbetterefficiency.ThehighspeedrectificationisalsoagoodcharacteristicofSchottkydiodeforhighswitchingfrequency.Currentratingofthediodemustmeettherootmeansquareofthepeakcurrentandoutputaveragecurrentmultiplicationasfollowing:PEAKOUTDIIRMSI×≈)(Thediode’sreversebreakdownvoltageshou