PCBdesignforreduceEMI

1PCBDesignGuidelinesForReducedEMISZZA009November19992IMPORTANTNOTICETexasInstrumentsanditssubsidiaries(TI)reservetherighttomakechangestotheirproductsortodiscontinueanyproductorservicewithoutnotice,andadvisecustomerstoobtainthelatestversionofrelevantinformationtoverify,beforeplacingorders,thatinformationbeingreliedoniscurrentandcomplete.Allproductsaresoldsubjecttothetermsandconditionsofsalesuppliedatthetimeoforderacknowledgement,includingthosepertainingtowarranty,patentinfringement,andlimitationofliability.TIwarrantsperformanceofitssemiconductorproductstothespecificationsapplicableatthetimeofsaleinaccordancewithTI’sstandardwarranty.TestingandotherqualitycontroltechniquesareutilizedtotheextentTIdeemsnecessarytosupportthiswarranty.Specifictestingofallparametersofeachdeviceisnotnecessarilyperformed,exceptthosemandatedbygovernmentrequirements.CERTAINAPPLICATIONSUSINGSEMICONDUCTORPRODUCTSMAYINVOLVEPOTENTIALRISKSOFDEATH,PERSONALINJURY,ORSEVEREPROPERTYORENVIRONMENTALDAMAGE(“CRITICALAPPLICATIONS”).TISEMICONDUCTORPRODUCTSARENOTDESIGNED,AUTHORIZED,ORWARRANTEDTOBESUITABLEFORUSEINLIFE-SUPPORTDEVICESORSYSTEMSOROTHERCRITICALAPPLICATIONS.INCLUSIONOFTIPRODUCTSINSUCHAPPLICATIONSISUNDERSTOODTOBEFULLYATTHECUSTOMER’SRISK.Inordertominimizerisksassociatedwiththecustomer’sapplications,adequatedesignandoperatingsafeguardsmustbeprovidedbythecustomertominimizeinherentorproceduralhazards.TIassumesnoliabilityforapplicationsassistanceorcustomerproductdesign.TIdoesnotwarrantorrepresentthatanylicense,eitherexpressorimplied,isgrantedunderanypatentright,copyright,maskworkright,orotherintellectualpropertyrightofTIcoveringorrelatingtoanycombination,machine,orprocessinwhichsuchsemiconductorproductsorservicesmightbeorareused.TI’spublicationofinformationregardinganythirdparty’sproductsorservicesdoesnotconstituteTI’sapproval,warrantyorendorsementthereof.Copyright1999,TexasInstrumentsIncorporatediiiContentsTitlePageABSTRACT1.......................................................................................1Background1.....................................................................................1.1RFSources1................................................................................1.2Surface-MountDevicesvsThrough-HoleComponents1..............................................1.3StaticPinsvsActivePinsvsInputs1.............................................................1.4BasicLoops2................................................................................1.4.1ProportionalityofLoopsandDipoles3.....................................................1.5DifferentialvsCommonMode3.................................................................2BoardLayout4....................................................................................2.1GroundsandPower4..........................................................................2.1.1Inductance4...........................................................................2.1.2Two-LayervsFour-LayerBoards4.........................................................2.1.3MicrocomputerGroundsinOne-andTwo-LayerDesigns5.....................................2.1.4SignalReturnGrounds5.................................................................2.1.5AnalogvsDigitalvsHighPower5.........................................................2.1.6AnalogPower-SupplyPinsandAnalogReferenceVoltages6....................................2.1.7PowerPlaneDo’sandDont’sforFour-LayerBoards6.........................................2.2PowerDistributionforTwo-LayerBoards7...................................................2.2.1Single-PointvsMultipointDistribution7....................................................2.2.2StarDistribution7......................................................................2.2.3GriddingtoCreatePlanes7...............................................................2.2.4BypassingandFerriteBeads9............................................................2.2.5KeepingNoiseClosetotheChip11........................................................2.3BoardZoning12.........................................................................2.4SignalTraces13..............................................................................2.4.1CapacitiveandInductiveCrosstalk13......................................................2.4.2AntennaFactorLengthRules13...........................................................2.4.3SeriesTermination,TransmissionLines13...................................................2.4.4ImpedanceMatchingatInputs14..........................................................2.5CablesandConnectors14......................................................................2.5.1Differential-ModeandCommon-ModeNoise14..............................................2.5.2CrosstalkModel14.....................................................................2.5.3NumberofReturns15...................................................................2.5.4I/ORecommendationsforOff-PCBSignals15......................