EMC Design Considerations d.pdf

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1、AVR040:EMCDesignConsiderationsScope8-bitThisapplicationnotecoversthemostcommonEMCproblemsdesignersencounterMicrocontrollerswhenusingmicrocontrollers.Itwillbrieflydiscussthevariousphenomena.ThereferenceliteraturecoversEMCdesigninmoredetail,andfordesigne

2、rswhoaregoingtobuildproductsthatneedtobeEMCcompliant,furtherstudyishighlyrecommended.AgoodEMCdesignrequiresmoreknowledgethanwhatcanbeApplicationNoteputintoashortapplicationnote.Unlikemanyotherdesignissues,EMCisnotanareawhereitispossibletolistasetofrule

3、s.EMCcompliancecannotbeguaranteedbydesign;ithastobetested.ItisrecommendedthatreadersunfamiliarwithEMCdesignreadthisdocumentPRELIMINARYmorethanonce,assomeofthesubjectsdescribedearlyinthisdocumentaremoreeasilyunderstoodifthereaderhasalreadyreadtherestoft

4、hedocument.1IntroductionElectromagneticcompatibilityisasubjectmostdesignersdidnothavetoworryaboutafewyearsago.Today,everydesignerputtingaproductontheglobalmarkethastoconsiderthis.Therearetwomainreasonsforthis:•Theelectromagneticenvironmentisgettingtoug

5、her.High-frequencyradiotransmitters,likemobiletelephones,arefoundeverywhere.Moreandmoresystemsareusingswitchingpowersuppliesinthepowercircuit,andtheoverallnumberofelectronicappliancesisincreasingeveryyear.•Electroniccircuitsarebecomingmoreandmoresensit

6、ive.Powersupplyvoltagesaredecreasing,reducingthenoisemarginofinputpins.Circuitgeometriesgetsmallerandsmaller,reducingtheamountofenergyrequiredtochangealogiclevel,andatthesametimereducingtheamountofnoiserequiredtoalterthelogicvaluesofsignals.Fromadesign

7、er’spointofview,EMCphenomenahavetobeconsideredintwodifferentways:•Howtheenvironmentmayaffectthedesign(immunity).•Howthedesignmayaffecttheenvironment(emission).Traditionally,theonlygovernmentregulationshavebeenontheemissionside:Anelectronicdeviceisnotal

8、lowedtoemitmorethanacertainamountofradiofrequencyenergytoavoiddisturbingradiocommunicationoroperationofotherRev.1619D-AVR-06/06electronicequipment.Mostcountriesintheworldhaveregulationsonthistopic.Additionaldemandsonnoiseimmunityearlier