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1、AN-703APPLICATIONNOTEOneTechnologyWay•P.O.Box9106•Norwood,MA02062-9106•Tel:781/329-4700•Fax:781/326-8703•www.analog.comDrivingHighPowerLEDsbyYuxinLi,GangLiu,andAlanLiINTRODUCTIONThecurrentsensingresistoralongwiththevoltageatTheADP3806isaswitchingmodepowersupply(SMPS)theISETpindeterm
2、inestheoutputcurrent.Therequiredcontrollerfeaturingdualloopconstant-voltageandvoltageattheISETpinshouldbegeneratedfromtheconstant-currentcontrol;remoteandaccuratecurrent2.5VprecisionreferencesourceREFpin.Themaximumsensing;andshutdownandprogrammable,synchro-outputcurrentfromtheREFpin
3、is500A.Togeneratenizableswitchingfrequency.Fordifferentapplicationahighersettingvoltage,thevoltagedividercanrunoffrequirements,itcanbeconfiguredinavarietyoftopologies:theREGpin(6V).NotethattheaccuracyforREFis1%,buck,boost,buck-boost,SEPIC,andCUK.ThisapplicationandtheaccuracyforREGis
4、3%.noteguidesthedesignsofcontrollercircuitsfordrivingAcrossCS+andCS–pins,afiltercapacitorofabout220nFhighpowerLEDs(lightemittingdiodes)byusingtheshouldbeplacedrightnexttothepinsinthePCBlayoutADP3806toachieveanefficiencyofupto95%.tofilteroutnoise.Beforeusingthisapplicationnotefordesigni
5、ngthecir-cuits,downloadtheADP3806datasheetfromtheADIBUCKCONFIGURATIONwebsite.TodriveLEDswithanoutputvoltagelowerthantheinputpowersourcevoltage,astep-downtopologyBuckcanPOWERINGUPTHEADP3806beused.TheminimumVCCis6.25V(undervoltagelockoutUVLOFigure1showstheBuckconfigurationcircuit.This
6、voltage)andthemaximumVCCshouldnotexceed23V,schemeutilizesthesynchronousrectificationfunc-whichbringstheswitchdrivervoltageBSTto30V,thetionalityofthecontrollertoprovidethehighestpowerjunctionbreakdownvoltage.TherecommendedVCCconversionefficiency.Thecontrollerandthepowerrangeisfrom6.5V
7、to20V.stagecanbepoweredupbyeitherthesameordiffer-ToensureacleanvoltagesourceattheVCCpin,anRCentpowersources.Usingthesamepowersource,thebypassnetworkisusedbetweentheinputsourceandinputvoltagerangeshouldbewithintherangeof6.5VtheIC.Thedecouplingcapacitorcanbeinthevalueto20V.Withdiffere
8、ntpowersources,thep
