LM2621 Low Input Voltage, Step-Up DC-DC …

1 ProductFolderSample &BuyTechnicalDocumentsTools &SoftwareSupport &CommunityLM2621 SNVS033D MAY2004 REVISEDNOVEMBER2015LM2621 Low Input Voltage, step -UpDC-DCConverter1 Features3 DescriptionTheLM2621is a highefficiency, step -upDC-DC1 SmallVSSOP8 Package(Halfthe Footprintofswitchingregulatorfor battery-poweredand low inputStandard8-PinSOICP ackage) acceptsan inputvoltagebetween V and 14 V and convertsit into a regulatedoutput Up to outputvoltagecan be and 14 V. It has an N-Channel to 90%are 14-VAdjustableOutputVoltageachievableusi ngthe LM2621 . Up to 1A LoadCurrentThehighswitchingfrequency(adj ustableup to 2 InternalMOSFETMHz)of the LM2621allowsfor tiny surfacemount Up to 90% the uniqueconstant-duty-cyclegatedoscillator topologyvery 80- A TypicalOperatingCurrenthighefficienciesa re realizedovera wideloadrange.

2 < A SpecifiedSupplyCurrentIn ShutdownThe supplycurrentis reducedto 80 A becauseofthe the shutdown2 Applicationsmode,the supplycurrentis less A. PDAs,CellularPhonesTheLM2621is availablein a VSSOP-8package. 2-Celland 3-CellBattery-OperatedEquipmentThispackageuseshalf the boardareaof a standard8-pinSOICand has a heightof just PCMCIAC ards,MemoryCards FlashMemoryProgrammingDeviceInformation(1) TFT/LCDA pplicationsPARTNUMBERPACKAGEBODYSIZE(NOM) (8) x GPSD evices(1) For all availablepackages,see the orderableaddendumat Two-WayPagersthe end of the datasheet. PalmtopComputers Hand-HeldInstrumentsTypicalApplicationCircuit1An IMPORTANTNOTICEat the end of this datasheetaddressesavailability,warranty,changes,use in safety-criticalapplications,intellectualpropertymattersand MAY2004 Contents1 Applicationand Pin Configurationand Deviceand Mechanical,Packaging,and RevisionHistoryChangesfromRevisionC (November2012)to RevisionDPage AddedPin Configurationand Functionssection,HandlingRatingtable,FeatureDescriptionsection,DeviceFunctionalModes,Applicationand Implementationsection,PowerSupplyRecommendationssection,Layoutsection,Deviceand DocumentationSupportsection,andMechanical,Packaging,and 2004 2015, MAY2004 REVISEDNOVEMBER20155 Pin Configurationand FunctionsDGKP ackage8-PinVSSOPTop ViewPin FunctionsPINTYPE(1)

3 Externalresistorconnectedbetweenthis pin and Pin 6 (VDD) sets the switchingfrequencyof the InternalCircuitryBOOT7 PWRB ootstrapSupplyfor the GateDriveof InternalMOSFETP owerSwitchSW8 PWRD rainof the InternalMOSFETP owerSwitch(1)I = Input ,O = Output,PWR= Power,GND= Ground,A = Analog6 (1)(2)MINMAXUNITSW Pin voltage ,VDD, EN and FB Pins APowerDissipation(TA=25 C)(3)500mWTJmax(3)150 CLeadTemp.(Soldering,5 sec)260 CStoragetemperature,Tstg 65150 C(1)StressesbeyondthoselistedunderAbsolu teMaximumRatingsmay causepermanentdamageto the stressratingsonly,whichdo not implyfunctionaloperationof the deviceat theseor any otherconditionsbeyondthoseindicatedunder RecommendedOperatingConditions. Exposureto absolute-maximum-ratedconditionsfor extendedperiodsmay affectdevicereliability.(2)If Military/Aerospacespecifieddevicesare required,pleasecontactthe TexasInstrumentsSalesOffice/Distributors for availabilityandspecifications.

4 (3)The maximumpowerdissipationmustbe deratedat elevatedtemperaturesand is dictatedby Tjmax(maximumjunctiontemperature), JA(junctionto ambientthermalresistance),and TA(ambienttemperature).The maximumallowablepowerdissipationat anytemperatureis Pdmax= (Tjmax- TA)/ JAor the numbergivenin the AbsoluteMaximumRatings,whicheveris 2004 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback3 ProductFolderLinks:LM2621LM2621 SNVS033D MAY2004 (unlessotherwisenoted) ,TA 4085 (1)DGK(VSSOP)UNIT8 PINSR JAJunction-to-ambientthermalresistance(2 )160 C/WR JC(top)Junction-to-case(top) C/WR C/W C/W C/WR JC(bot)Junction-to-case(bottom)thermalre sistanceN/A C/W(1)For moreinformationabouttraditionaland new thermalmetrics,see theSemiconductorand IC PackageThermalMetricsapplicationreport,S PRA953.(2)The maximumpowerdissipationmustbe deratedat elevatedtemperaturesand is dictatedby Tjmax(maximumjunctiontemperature), JA(junctionto ambientthermalresistance),and TA(ambienttemperature).

5 The maximumallowablepowerdissipationat anytemperatureis Pdmax= (Tjmax- TA)/ JAor the numbergivenin the AbsoluteMaximumRatings,whicheveris :VDD= VOUT= V, TJ= 25 0 (1)ILOAD= 0 mA, 40 C to 85 0 (oncestarted)VFBFB Pin 40 C to 85 (2)30mV 40 C to 85 C45 EfficiencyVIN= V; VOUT= 5 V; ILOAD= 500 mA87%VIN= V; VOUT= V; ILOAD= 200 mA87%DSwitchDutyCycle70% 40 C to 85 C60%80%IDDO peratingQuiescentFB Pin > V; EN Pin at VDD80 ACurrent(3)FB Pin > V; EN Pin at VDD, 40 C to 85 C110 ISDS hutdownQuiescentVDD, BOOTand SW Pinsat V; EN Pin < (4)mV AVDD, BOOTand SW Pinsat V; EN Pin < , 40 C to 85 (1)Outputin regulation,VOUT= VOUT(NOMINAL) 5%(2)This is the hysteresisvalueof the internalcomparatorusedfor the gated-oscillatorcontrolscheme.(3)This is the currentinto the VDDpin.(4)This is the total currentinto pins VDD, BOOT,SW and 2004 2015, MAY2004 REVISEDNOVEMBER2015 ElectricalCharacteristics(continued)Unle ssotherwisespecified:VDD= VOUT= V, TJ= 25 ResistanceENABLESECTIONVEN_LOEN Pin VoltageLow(5) 40 C to 85 Pin VoltageHigh(5) 40 C to 85 (5)Whenthe EN pin is belowVEN_LO, the regulatoris shut down;whenit is aboveVEN_HI, the regulatoris VVOUT= VFigure1.

6 Efficiencyvs LoadCurrentFigure2. Efficiencyvs LoadCurrentFigure3. VFBvs TemperatureFigure4. IOPvs TemperatureCopyright 2004 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback5 ProductFolderLinks:LM2621LM2621 SNVS033D MAY2004 (continued)Figure5. ISDvs TemperatureFigure6. ISDvs VDDVOUT= VFigure7. IOPvs VDDF igure8. VIN_STvs LoadCurrentFigure10. PeakInductorCurrentvs LoadCurrentFigure9. SwitchingFrequencyvs RFQ6 SubmitDocumentationFeedbackCopyright 2004 2015, MAY2004 REVISEDNOVEMBER2015 TypicalCharacteristics(continued)Figure1 1. MaximumLoadCurrentvs InputVoltageCopyright 2004 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback7 ProductFolderLinks:LM2621LM2621 SNVS033D MAY2004 LM2621is designedto providestep-upDC-DCvoltageregulationin battery-poweredand combinesa step -upswitchingregulator,N-channelpower MOSFET,built-incurrentlimit,thermallimit ,and voltagereferencein a single8-pinVSSOP packagePin Configurationand Functions.

7 The switchingDC-DCregulatorboostsan V and 14 V to a 14 V. The LM2621startsfroma low remainsoperationaldownto optimizedfor use in cellularphonesand otherapplicationsrequiringa smallsize,low profile,aswell as low quiescentcurrentfor maximumbatterylife duringstand-byand high-efficiencygated-oscillatortopologyo ffersan outputof up to 1 built-inpeakswitchcurrentlimit,and uniquegatedoscillatorcontrolschemeenable sthe LM2621to havean ultra-lowquiescentcurrentandprovidesa highefficiencyovera the internaloscillatorisprogrammableusingan externalresistorand can be set between300 kHz and 2 hysteresiswindowto regulatethe outputvoltageis belowthe upperthresholdof the window,the LM2621switchescontinuouslywitha fixeddutycycleof 70%at theswitchingfrequencyselectedby the first part of eachswitchingcycle,the internalN-channelMOSFET switchis turnedon.

8 Thiscausesthe currentto rampup in the inductorand of eachswitchingcycle,the MOSFETis turnedoff. The voltageacrossthe inductorreversesandforcescurrentthrought he diodeto the outputfiltercapacitorand the LM2621switchescontinuously,the outputvoltagestartsto rampup. Whenthe outputvoltagehits the upperthresholdof thewindow,the outputvoltageto droopbecausethe energystoredin the outputcapacitoris depletedby the outputvoltagehits the lowerthresholdof thehysteresiswindow,the LM2621startsswitchingcontinuouslyagainca usingthe outputvoltageto rampuptowardsthe showsthe switchvoltageand this typeof controlscheme,the quiescentcurrentis inherentlyverylow. At lightloadsthe gatedoscillatorcontrolschemeoffersa muchhigherefficiencycomparedto the 2004 2015, MAY2004 REVISEDNOVEMBER2015 FeatureDescription(continued)Figure12.

9 LM2621can start-upfrominputvoltagesas low as V. On start-up,the controlcircuitryswitchesthe N-channelMOSFET continuouslyat 70%duty cycleuntil the V. Afterthis outputvoltageis reached,the normalstep-upregulatorfeedbackand in regulationit can operatedownto a ,sincethe internalpowerfor the IC can be boot-strappedfromthe outputusingthe majorcomponentof the outputvoltagerippleis due to the hysteresisusedin the frequencyof this voltagerippleis proportionalto the load frequencyof this rippledoesnot necessitatethe use of largerinductorsand capacitorshowever,sincethe sizeof thesecomponentsisdeterminedby the switchingfrequencyof the oscillatorwhichcan be set up to 2 MHzusingan ThermalProtectionAn internalcycle-by-cyclecurrentlimit servesas a set highenough( typical,approximately4 A maximum)so as not to comeinto internalthermalprotectioncircuitrydisabl esthe MOSFET powerswitchwhenthe junctiontemperature(TJ) exceedsabout160 C.

10 The switchis re-enabledwhenTJdropsbelowapproximately1 35 LM2621featuresa shutdownmodethat reducesthe quiescentcurrentto lessthana life of the batteryin ,allfeedbackand controlcircuitryis turnedoff. The regulator'soutputvoltagedropsto one the shutdownmodeis controlledby the active-lowlogicinputpin EN (Pin 2). Whenthelogicinputto this pin , the devicegoesinto logicinputto this pinshouldbe VDDfor the deviceto workin 2004 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback9 ProductFolderLinks:LM2621LM2621 SNVS033D MAY2004 Applicationand ImplementationNOTEI nformationin the followingapplicationssectionsis not partof the TI componentspecification,and TI doesnot warrantits accuracyor s customersareresponsiblefor determiningsuitabilityof componentsfor test theirdesignimplementationto LM2621is primarilyusedas a followingsectionprovidesinformationregar dingconnectionandcomponentchoicesto builda typicalapplicationsare alsoprovidedincludinga SEPIC step - designingaSEPIC convertercan be orderto successfullybuildan application,the designershouldhavethe followingparameters.