ESD保护设计研讨会(英文)

ESDProtectionDesignSeminarJimSutherlandSeniorApplicationsEngineerOutlineWhatisESD?Whatdamagecanitcause?Whyistheproblemgrowing?Whataretheissuesforthedesigner?Howcanwemeasureit?HowcanweprotectequipmentfromESD?WhatIsESD?ESD=ElectroStaticDischargeGenerationTriboelectric(frictioncausesaccumulationofcharge)Induction(fieldinducescharge)DischargeDielectric(air)breakdownElectricfieldincreaseswhenchargedbodiesapproacheachotherCurrentflowintocircuitryESDDamageofICsPermanentOxidebreakdown,shorts,opens,latch-upTemporaryLatch-up,groundbounceLatentDegradationfromanESDeventESDproblemisgrowingCircuits/SystemsOld-RobustICs&LowspeedsignalsNew-SensitiveICs&HighspeedsignalsEnvironmentOld-Manufacturing/CorporateNew-Home/Outdoors/PersonESDIssuesfortheDesignerMustmeetESDspecificationsSelectESDtolerantcomponentsMinimizesignaldegradation(fromR,L&C)Boardspace/weight/properdesignComponentcostAssemblycostLifetimecost(stability)TestthesystemInternationalESDStandardsHumanBodyModel(HBM)-fordevicesEIA/JESD22-A114-AANSI/EOS/ESD-S5.1-1993MIL-STD-883(method3015)IEC1000-4-2:1995-forsystemsMachineModel(MM)-lesscommonEIA/JESD22-A115-AANSI/EOS/ESD-S5.1-1993ChargeDeviceModel(CDM)-lesscommonJESD22-c101HumanBodyModel(HBM)Dischargefrom100pFcapacitorthrough1.5kOhmresistor6ESDpulses3positive,3negative>1secseparationPin-to-pintestingN(N-1)/2combinationsUsedforcomponentcharacterizationWidelyusedHBMCurrentWaveformRiseTime:2nS<Tr<10nSIEC1000-4-2:1995StandardDischargefrom150pFcapacitorthrough330ohmresistor6ESDpulses3positive,3negativeUsedforsystemcharacterization“Contact””v.“Air””dischargeDifferentlevelsDifferentapplicationsIEC1000-4-2CurrentWaveformVeryfastrisetime:Tr<1nS60nsIEC1000-4-2TestLevelsContactdischargeisthepreferredtestmethod-airdischargesarenotrepeatableAirdischargesusedwherecontactdischargecannotbeappliedNoimpliedequivalenceintestseveritybetweenthetwotestmethodsIEC1000-4-2BenchTestSpecificationESDProtectionTechniquesClampdiodesinICNotsufficientprotectionShieldingLoweffectivenessBypasscapacitororseriesresistor/inductorCandegradesignal;manycomponents;largeboardareaSparkgapLowcost;lowstability;largeboardareaDiscreteZenerdiodesHighcapacitance,manycomponents;largeboardareaDiscretePNdiodesLowcapacitance;manycomponents;largeboardareaIntegratedPNdiodesIntegratedDiodeNetworksSuperiordownstreamESDprotectionHighspeedresponseESDcurrentsteeredtoGNDorVCCMinimumSignalDegradation(LowC)Minimalboardspace,weightLowassembly/manufacturingcostsMinimalDesign-InTimeLong-termreliabilityChoosinganESDDiodeNetworkHowmanylinesareneeded?Howmuchcapacitance?(e.g.<5pF)WhatistheHBMrating?(e.g.±15kV)Whatisthedownstreamclampvoltage?(e.g.13V@15kVHBMpulse)Whatisthecontactdischargerating?(e.g.±±8kV)Whatistheairdischargerating?(e.g.±±15kV)Whatpackage?(e.g.24-pinQSOP)ESDDiodeNetworkPlacementTheNeedtoKeepESDDiodesDownstreamofLineInductancesAlsoputprotectiondiodesatmostlikelyESDentrypoint-theconnectorPreferredLayoutESDEntryPointParasiticLVccGndProtectedDevicePoorlayout-increasedclampvoltageduetoparasiticinductanceParasiticLVccGndProtectedDeviceESDEntryPointDesigningforMinimalPowerRailInductanceAddBypassCapacitorPlaceCeramicbypasscapacitor(0.1~0.2uF)ascloseaspossibletoESDdiodenetworkpowerrailtoshuntESDcurrenttobothpowerrailsMaybeaddZenerinparallelwithcapacitortominimizeparasiticinductanceofbypasscapacitorProtectedDeviceGndVccCUsingaSeriesResistorto

MinimizeDownstreamCurrentCanbeconsideredforlatch-upsensitiveapplicationsGuaranteedclampingvoltagelimitscurrentdownstream(I=V/R)OnlyforinputswithhighZOnlyforoutputdriverswithlowZwatchoutforfilteringofsignalPower-downIssuesDiodeprotectedsystemsthatarepowereddowncandraincurrentfromanactivehighinputthroughthediodetoVCCThiscandrainbatteriesand/ordamagedevicesonthesamelineToavoidthis,isolateVCCfromthebypasscapacitorwithablockingdiodeOnediodesolutionComponentandSystemSpecificationsThereisnosimpleformulatotranslatesystemspecificationsintocomponentspecificationsIEC1000-4-2SpecificationismoreseverethanHBMLinecapacitanceandinductanceshapetheESDpulse,reducingitspeakvaluePoordeviceplacementcandegradeperformanceIftherearemultipledevicesonaline,decidewhichtoprotectTherelationshipbetweendownstreamclampvoltageanddownstreamprotectionisnotexactValidatingtheDesignDefinethepracticallimitsoffunctionalfailure(e.g.Dataintegrity,recoverytime)TestonlyatthoseplacessubjecttotouchduringnormaloperationUseContactESDischargestocouplingplanes&conductivesurfaces,I/Opins,flexpads,andpowerpinsUseAirESDischargestoinsulatingsurfaces,openingsatedgesofkeys,flexcables,ventareas,seams,slots,apertures