电流采样方法

APPLICATIONNOTE—105Introduction-1INTRODUCTIONApplicationNote105December2005CurrentSenseCircuitCollectionMakingSenseofCurrentTimRegan,EditorThisApplicationNoteWillChangeSensingand/orcontrollingcurrentflowisafundamentalrequirementinmanyelectronicssystems,andthetech-niquestodosoareasdiverseastheapplicationsthem-selves.ThisApplicationNotecompilessolutionstocur-rentsensingproblemsandorganizesthesolutionsbygeneralapplicationtype.ThesecircuitshavebeenculledfromavarietyofLinearTechnologydocuments.ThisApplicationNoteisagrowingandchangingdocu-ment.Manyofthechapterslistedbelowareplaceholdersformaterialthatwillbefilledinsoon.Asthechaptersareadded,theirlinkswillbeenabled.UsingtheApplicationNoteClickthenameofachapterinthe“CircuitCollectionIn-dex”belowtoopenthePDFversionofthatchapter.CircuitsOrganizedbyGeneralApplicationEachchaptercollectstogetherapplicationsthattendtosolveasimilargeneralproblem,suchashighsidecur-rentsensing,ornegativesupplysensing.Thechaptersaretitledaccordingly(see“CircuitCollectionIndex”be-low).Inthisway,thereaderhasaccesstomanypossiblesolutionstoaparticularprobleminoneplace.ContributorsJonMunson,AlexiSevastopoulos,GregZimmer,MichaelStokowski,LTC,LTM,LT,BurstMode,OPTI-LOOP,Over-The-TopandPolyPhaseareregisteredtrademarksofLinearTechnologyCorporation.AdaptivePower,C-Load,DirectSense,EasyDrive,FilterCAD,HotSwap,LinearView,µModule,MicropowerSwitcherCAD,MultimodeDimming,NoLatency∆Σ,NoLatencyDelta-Sigma,NoRSENSE,OperationalFilter,PanelPro-tect,PowerPath,PowerSOT,SmartStart,SoftSpan,StageShedding,SwitcherCAD,ThinSOT,UltraFastandVLDOaretrademarksofLinearTechnologyCorporation.Otherproductnamesmaybetrademarksofthecompaniesthatmanufacturetheproducts.Itisunlikelythatanyparticularcircuitshownwillexactlymeettherequirementsforaspecificdesign,butthesug-gestionofmanycircuittechniquesanddevicesshouldproveuseful.Specificcircuitsmayappearinseveralchaptersiftheyhavebroadapplication.CIRCUITCOLLECTIONINDEXLevelShiftingHighSpeedCurrentSenseBasicsHighVoltageFaultSensingHighSideLowVoltageDigitizingLowSideHighCurrent(100mAtoAmps)CurrentControlNegativeVoltageUnidirectionalPrecisionLowCurrent(PicoampstoMilliamps)BidirectionalACMotorsandInductiveLoadsDCBatteriesWideRangeAPPLICATIONNOTE105:CurrentSenseCircuitCollectionCurrentSenseBasicsThischapterintroducesthebasictechniquesusedforsensingcurrent.Itservesalsoasadefinitionofcommonterms.Eachtechniquehasadvantagesanddisadvan-tagesandthesearedescribed.Thetypesofamplifiersusedtoimplementthecircuitsareprovided.ToseeotherchaptersinthisApplicationNote,returntotheIntroduction.LOWSIDECURRENTSENSINGCurrentsensedinthegroundreturnpathofthepowerconnectiontothemonitoredload.Currentgenerallyflowsinjustonedirection(uni-directional).Anyswitch-ingisperformedontheload-sideofmonitor.–+ILOADISENSELOADOUTPUT∝ILOADDCVSUPPLYVCCRSENSE.LowSideAdvantagesLowinputcommonmodevoltageGroundreferencedoutputvoltageEasysinglesupplydesignLowSideDisadvantagesLoadliftedfromdirectgroundconnectionLoadactivatedbyaccidentalshortatgroundendloadswitchHighloadcurrentcausedbyshortisnotdetectedAmplifierTypesforLowSideImplementationPrecisionzero-driftopamps:LTC2050,LTC2054Instrumentationamplifiers:LTC2053,LT1990,LTC6943Rail-to-RailInputopamps:LT1677HIGHSIDECURRENTSENSINGCurrentsensedinthesupplypathofthepowerconnec-tiontothemonitoredload.Currentgenerallyflowsinjustonedirection(uni-directional).Anyswitchingisper-formedontheload-sideofmonitor.–+ILOADISENSELOADOUTPUT∝ILOADDCVSUPPLYRSENSEHighSideAdvantagesLoadisgroundedLoadnotactivatedbyaccidentalshortatpowercon-nectionHighloadcurrentcausedbyshortisdetectedHighSideDisadvantagesHighinputcommonmodevoltages(oftenveryhigh)Outputneedstobelevelshifteddowntosystemoper-atingvoltagelevelsAmplifierTypesforHighSideImplementationDedicatedcurrentsensingamplifiers:LT6100,LTC6101,LT1787Over-the-Top™opamps:LT1637Flyingcapacitoramplifier:LTC6943CurrentSenseBasics-1APPLICATIONNOTE105:CurrentSenseCircuitCollectionFULL-RANGE(HIGHANDLOWSIDE)CURRENTSENSINGBi-directionalcurrentsensedinabridgedrivenload,orunidirectionalhighsideconnectionwithasupplysideswitch.–+ILOADISENSEOUTPUT∝ILOADDCVSUPPLYVCCRSENSELOADFull-RangeAdvantagesOnlyonecurrentsenseresistorneededforbidirec-tionalsensingConvenientsensingofloadcurrenton/offprofilesforinductiveloadsFull-RangeDisadvantagesWideinputcommonmodevoltageswingsCommonmoderejectionmaylimithighfrequencyaccuracyinPWMapplicationsAmplifierTypesforBi-directionalImplementationDifferenceamplifiers-LT1990,LT1991,LT1995,LT1996Instrumentationamplifiers:LTC2053Flyingcapacitoramplifier:LTC6943SUMMARYOFCURRENTSENSESOLUTIONSThenextfewpagescontainatablethatsummarizescur-rentsensesolutionsandapplicabledevices.Lookfirstinthe“Type/Circuit”columnandthe“Gain”columnforageneraldescriptionoftheapplication.Thenscanacrosstheothercolumnsforapplicabledevicesandtheirspeci-fications.CurrentSenseBasics-2APPLICATIONNOTE105:CurrentSenseCircuitCollectionCurrentSenseBasics-3ACCURACYSPEEDTYPE/CIRCUITGAIN(V/V)DEVICESANDPACKAGESOFFSETVOLTAGE(VOS)INPUTCURRENT(IBIAS)BANDWIDTHSLEWRATEVSUPPLYRANGE(VS)VINRANGE(VCM)DIFFER