PHY芯片LAYOUT注意事项

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1、AN18.6SMSCEthernetPhysicalLayerLayoutGuidelines1IntroductionSMSCEthernetproductsarehighly-integrateddevicesdesignedfor10or100MbpsEthernetsystems.TheyarebasedonIEEE10BASE-Tand100BASE-TXstandards.TheIEEE802.3-2005standardfor100BASE-TXdefinesnetworkingovertwopairsofCategory5unshieldedtwisted

2、paircableorType1shieldedtwistedpaircable.ThisapplicationnoteisintendedtoassistcustomersindesigningaPCBusingSMSC’sEthernetproductstointerfacewithanEthernetnetwork.ThisdocumentprovidesrecommendationsregardingthePCBlayout.Thisisacriticalcomponentinmaintainingsignalintegrity,andreducingEMI.1.

3、1AudienceThisapplicationnoteiswrittenforareaderthatisfamiliarwithEthernethardwaredesign.1.2OverviewThefollowingrecommendationsfortheprintedcircuitboardlayoutwithSMSCpartsarenottheonlywaytolayoutSMSCEthernetQFP/QFNparts.Everyboarddesignerwillhaveapreference.Complexity,boardspace,numberandt

4、ypesofdeviceswilldictateroutingandplacementstrategies.Forexample,thePCBdescribedinthisapplicationnotehascomponentsonbothsidesoftheboard.Afourlayerboardcouldberealizedwithcomponentsononesideonly.ThedatasheetsandreferenceschematicsforSMSCEthernetproductsshouldbeusedasareferenceforthislayout

5、designguideline.2GeneralDesignGuidelinesTheEvaluationBoard(EVB)schematicsandgerberfilesareavailableontheSMSCwebsite.Thesecanbeusedasareferenceforcomponentplacementandrouting.Goodengineeringpracticesshouldbefollowedwithrespecttounusedinputsbyterminatingthemwithpull-uporpull-downresistors,u

6、nlessthedatasheet,designguideorreferenceschematicindicatesotherwise.Donotattachpull-uporpull-downresistorstoanypinsidentifiedasreserved(unlessexplicitlystatedinthedatasheet).Thesedevicesmayhavespecialtestmodesthatcouldbeenteredinadvertently.2.1IndustrialTemperatureWhendesigningwiththeindu

7、strialtemperatureversionofthePHY,careneedstobegiventothetemperaturerangeofthesupportingcomponents.Iftheendapplicationrequiresindustrialtemperaturesupport,thenthesystemdesignerneedstoselectallpertinentcomponentstobefunctionalintheindustrialtemperaturerange.SMSCAN18.6