搜索
July2007LM27330.6/1.6MHzBoostConvertersWith40VInternalFETSwitchinSOT-23GeneralDescriptionTheLM2733switchingregulatorsarecurrent-modeboostconvertersoperatingfixedfrequencyof1.6MHz(“X”option)and600kHz(“Y”option).TheuseofSOT-23package,madepossiblebytheminimalpowerlossoftheinternal1Aswitch,anduseofsmallinduc-torsandcapacitorsresultintheindustry'shighestpowerdensity.The40Vinternalswitchmakesthesesolutionsper-fectforboostingtovoltagesof16Vorgreater.Thesepartshavealogic-levelshutdownpinthatcanbeusedtoreducequiescentcurrentandextendbatterylife.Protectionisprovidedthroughcycle-by-cyclecurrentlimitingandthermalshutdown.Internalcompensationsimplifiesde-signandreducescomponentcount.SwitchFrequencyXY1.6MHz0.6MHzFeatures■40VDMOSFETswitch■1.6MHz(“X”),0.6MHz(“Y”)switchingfrequency■LowRDS(ON)DMOSFET■Switchcurrentupto1A■Wideinputvoltagerange(2.7V–14V)■Lowshutdowncurrent(1µA)■5-LeadSOT-23package■Usestinycapacitorsandinductors■Cycle-by-cyclecurrentlimiting■InternallycompensatedApplications■WhiteLEDCurrentSource■PDA’sandPalm-TopComputers■DigitalCameras■PortablePhonesandGames■LocalBoostRegulatorTypicalApplicationCircuit2005542420055457©2007NationalSemiconductorCorporation200554(0.6or1.6MHz)usingcurrent-modecontrolforfasttransientresponseoverawideinputvoltagerangeandincorporatepulse-by-pulsecurrentlimitingprotection.Becausethisiscurrentmodecontrol,a50mΩsenseresistorinserieswiththeswitchFETisusedtoprovideavoltage(whichisproportionaltotheFETcurrent)toboththeinputofthepulsewidthmodulation(PWM)comparatorandthecur-rentlimitamplifier.Atthebeginningofeachcycle,theS-RlatchturnsontheFET.AsthecurrentthroughtheFETincreases,avoltage(propor-tionaltothiscurrent)issummedwiththerampcomingfromtherampgeneratorandthenfedintotheinputofthePWMcomparator.Whenthisvoltageexceedsthevoltageontheotherinput(comingfromtheGmamplifier),thelatchresetsandturnstheFEToff.SincethesignalcomingfromtheGmamplifierisderivedfromthefeedback(whichsamplesthevoltageattheoutput),theactionofthePWMcomparatorconstantlysetsthecorrectpeakcurrentthroughtheFETtokeeptheoutputvolatgeinregulation.Q1andQ2alongwithR3-R6formabandgapvoltagerefer-enceusedbytheICtoholdtheoutputinregulation.ThecurrentsflowingthroughQ1andQ2willbeequal,andthefeedbackloopwilladjusttheregulatedoutputtomaintainthis.Becauseofthis,theregulatedoutputisalwaysmaintainedatavoltagelevelequaltothevoltageattheFBnodemultipliedupbytheratiooftheoutputresistivedivider.Thecurrentlimitcomparatorfeedsdirectlyintotheflip-flop,thatdrivestheswitchFET.IftheFETcurrentreachesthelimitthreshold,theFETisturnedoffandthecycleterminateduntilthenextclockpulse.ThecurrentlimitinputterminatesthepulseregardlessofthestatusoftheoutputofthePWMcom-parator.(Note1)IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.StorageTemperatureRange−65°Cto+150°COperatingJunctionTemperatureRange−40°Cto+125°CLeadTemp.(Soldering,5sec.)300°CPowerDissipation(Note2)InternallyLimitedFBPinVoltage−0.4Vto+6VSWPinVoltage−0.4Vto+40VInputSupplyVoltage−0.4Vto+14.5VShutdownInputVoltage(Survival)−0.4Vto+14.5VθJ-A(SOT23-5)265°C/WESDRating(Note3)HumanBodyModelMachineModel2kV200VElectricalCharacteristicsLimitsinstandardtypefaceareforTJ=25°C,andlimitsinboldfacetypeapplyoverthefulloperatingtemperaturerange(−40°C≤TJ≤+125°C).Unlessotherwisespecified:VIN=5V,VSHDN=5V,IL=0A.SymbolParameterConditionsMin(Note4)Typical(Note5)Max(Note4)UnitsVINInputVoltage2.714VISWSwitchCurrentLimit(Note6)1.01.5ARDS(ON)SwitchONResistanceISW=100mA500650mΩSHDNTHShutdownThresholdDeviceON1.5VDeviceOFF0.50ISHDNShutdownPinBiasCurrentVSHDN=00µAVSHDN=5V02VFBFeedbackPinReferenceVoltageVIN=3V1.2051.2301.255VIFBFeedbackPinBiasCurrentVFB=1.23V60nAIQQuiescentCurrentVSHDN=5V,SwitchingX2.13.0mAVSHDN=5V,SwitchingY1.12VSHDN=5V,NotSwitching400500µAVSHDN=00.0241FBVoltageLineRegulation2.7V≤VIN≤14V0.02%/VFSWSwitchingFrequency“X”Option1.151.61.85MHz“Y”Option0.400.600.8DMAXMaximumDutyCycle“X”Option8793%“Y”Option9396ILSwitchLeakageNotSwitchingVSW=5V1µANote1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothecomponentmayoccur.Electricalspecificationsdonotapplywhenoperatingthedeviceoutsideofthelimitssetforthundertheoperatingratingswhichspecifytheintendedrangeofop