开关电源PCB布局指南英文版（完整版）实用资料(可以直接使用，可编辑完整版实用资料，欢迎下载）SIMPLESWITCHER®PCBLayoutGuidelinesINTRODUCTIONOneproblemwithwritinganApplicationNoteonPCBlayoutisthatthepeoplewhoreaditareusuallynottheoneswhoaregoingtouseit.Evenifthedesignerhasstruggledthroughelectromagneticfields,EMC,EMI,boardparasitics,transmissionlineeffects,grounding,etc.,hewillinallprob-abilitythengoonwithhisprimarydesigntask,leavingthelayouttotheCAD/layoutperson.Unfortunately,especiallywhenitcomestoswitchingregulators,itisnotenoughtobeconcernedwithjustbasicrouting/connectivityandmechani-calissues.BoththedesignerandtheCADpersonneedtobeawarethatthedesignofaswitchingpowercon-verterisonlyasgoodasitslayout.Whichprobablyex-plainswhyagreatmanyofcustomercallsreceived,con-cerningswitcherapplications,areultimatelytracedtopoorlayoutpractices.Sadly,thesecouldandshouldhavebeenavoidedontheveryfirstprototypeboard,savingtimeandmoneyonallsides.TheoverallsubjectofPCBdesignisanextremelywideone,embracingseveraltest/mechanical/productionissuesandalsoinsomecasescompliance/regulatoryissues.Thereisalsoacertainamountofphysics/electromagneticsinvolved,ifaclearerunderstandingissought.ButthepurposeofthisApplicationNoteistoreachtheaudiencemostlikelytouseit.Thoughthereisenoughdesigninformationforthemoreexperienceddesigner/CADperson,theApplicationNotein-cludesaquick-setofclearandconcisebasicrulesthatshouldbescrupulouslyfollowedtoavoidamajorityofprob-lems.Inparticular,wehaveprovidedrecommendedstart-ingpointsforlayoutwhenusingthepopularLM267x,LM259xandLM257xfamilies(Figure2Thefocusisonthestep-down(BuckSimpleSwitcherICsfromNational,butthesameprinciplesholdforanytopologyandswitchingpowerapplication.Quick-SetofRulesforSIMPLESWITCHERPCBLayout(BuckaPlacethecatchdiodeandinputcapacitorasshowninFigure2.cConnectviastoaGroundplaneifavailable(optional,marked‘X’inFigure2dIfviasfallundertabofSMTpowerdevice,theseareconsidered‘thermalvias’.Usecorrectdimensionsasdiscussedtoavoidproductionissues.Orplacetheviasclosetobutnotdirectlyunderthetab.eRout