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♦Precision Internal Sense ResistorMAX471General Description♦2%Accuracy OverTemperatureThe MAX471/MAX472are complete,bidirectional,high-side current-sense amplifiersfor portablePCs,telephones,♦Monitors BothCharge andDischargeand othersystems wherebattery/DC power-line monitoring♦3A Sense Capability withInternalSense Resistoris critical.High-side power-line monitoringis especiallyMAX471useful inbattery-powered systems,since itdoes notinterferewith theground pathsof thebattery chargersor♦Higher Current-SenseCapabilitywith Externalmonitorsoften foundin“smart batteries.SenseResistorMAX472The MAX471has aninternal35mQ current-sense resistor♦100pA MaxSupply Currentandmeasures batterycurrents up to±3A.For applications♦18pA MaxShutdown Moderequiringhigher currentor increasedflexibility,theMAX472functions withexternal senseand gain-set-ting♦3V to36V SupplyOperationresistors.Both deviceshave a current outputthat can be♦8-Pin DIP/SO Packagesconvertedto aground-referred voltagewith asingleresistor,allowing awide rangeof batteryvoltages andcurrents.Ordering InformationAnopen-collector SIGN output indicatescurrent-flowdirection,so theuser canmonitor whethera batteryis TEMP.RANGEbeing chargedor discharged.Both devicesoperate from0℃to+70℃3V to36V,draw less than lOOpAover temperature,and0℃to+70℃include a18pA maxshutdown mode.-40℃to+85℃PART PIN-PACKAGE________________________Applications-40℃to+85℃MAX471CPA8Plastic DIP0℃to+70℃Portable PCs:MAX471CSA8SO0℃to+70℃Notebooks/Subnotebooks/Palmtops MAX471EPA8Plastic DIP-40℃to+85℃MAX471ESA8SOSmart BatteryPacks-40℃to+85℃8Plastic DIPMAX472CPACellular Phones8SOMAX472CSAPortable Phones8Plastic DIPMAX472EPA8SOPortable Test/Measurement SystemsMAX472ESABattery-Operated SystemsEnergyManagement SystemsTypical Operating Circuit____________________________Features Pin Configurations♦Complete High-Side CurrentSensingR-RS ILQADKTOPVIEWLCADorO-mGKR-RSLOGCSUPPIYSHDN18OUT100kR-27RS-37MAX471MAX471TO SIGNDISCHARGECHARGE R-36RS36Vour V3LTT1V/A GND45SIGNSHDNGbD ILQOODIP/SO20002kMAX472PinConfigurationcontinued onlast page.In Figure6,assume the load currentto be measured is10ATOLCWXHARGERand thatyou havedetermined a
0.3inch wide,2ouncecopper tobe appropriate.The resistivityof
0.1inch wide,
20.3OCFFK
0.1OCFFW
0.3OCFFKounce copperis30mQ/ft seeNote
4.For10A youmaywant RSENSE=5mQ for a50mV dropat fullscale.Thisresistor willrequire about2inches of
0.1inch widecopperPOA®3Vtrace.9OLR2E阳RG2CR TORG1and RG2EAT1H/36VOnce RSENSE is chosen,RG1and RG2can bechosen todefinethe current-gain ratioRSENSE/RG.Choose RG=RG1=RG2based on the followingcriteria:a1Q InputResistance.The minimumRG valueis limited1SHDN CUT8by the1Q inputresistance,and alsoby the output7current limitationsee below.As RG is reduced,the2N.C.
1.5kinput resistancebecomes a larger portionof the total3FG1R26gain-setting resistance.With RG=50Q,the input4GND SIGN5resistance producesa2%difference between theexpected andactual current-gain ratio.This is a gain1kerror thatdoes not affect linearityand can be removedbyadjusting RGor ROUT.Figure
6.MAX472Connections ShowingUse ofPC BoardTraceb Efficiency.As RGis reduced,loUTgets larger for agiven load current.Power dissipatedin ROUT is notmake sureRGis small enoughthat IBand losdo notgoingto the load,and thereforereduces overalladdany appreciableerrors.The full-scale erroris givenefficiency.This issignificant onlywhen the sense currentby:issmall.%Error=RG1-RG2x lB+losx RGx100飞c MaximumOutput CurrentLimitation.loUTis limitedto tsENSE
1.5mA,requiring RGVsENSE/
1.5mA.For VSENSE=wriert;r\o idiiu ndnare uieydin rebibiuib,bias current,is the小八bias-current mismatch,,„,OS._FS60mV,RG must be40Q.is the；d Headroom,The MAX472requires aminimum of
1.5V full-scale current,and Rei-OI=Kl obetweenthe lowerof the voltage atRG1or RG2VRG_SENSEisthe sense resistor.and VoUT.As RGbecomes larger,the voltagedropAssuming a5A load current,10mQ RSENSE,and100Qacross RGalso becomeslargerfora givenloUT.ThisRG,the current-gain ratiois lOOpA/A,yielding a full-scalevoltage dropfurther limitsthe maximumfull-scale VoilT.loUT of500pA.Using themaximum valuesfor IB20pAAssuming thedrop acrossRSENSE issmall andVccisand los2pA,and1%resistors for RG1and RG2RG1-connected to either side of RSENSE,VoUTmax=Vcc-RG2=2Q,the worst-case errorat fullscale calculates to:
1.5V+loilTmax xRG.2Q x20pA+100Q x2pA_048%e OutputOffset Errorat LowLoad Currents.Large RG5mQ x5Avalues reduceloUTfor agivenloadcurrent.As lOUTgets南黯威“借蜩建建黑黑鬻黑smaller,the
2.5pA maxoutput offset-error currentfbecomes alarger part of theoverall output current.Keeping the gain highby choosinga lowvalue forRGRG.minimizes this offset error.Current-Sense AdjustmentfInput BiasCurrent andInput BiasCurrentResistor Range,Output AdjustMismatching.The sizeof RGalso affectsthe errorsChoose ROUT afterselecting RSENSE,RG1,and RG
2.introduced bythe input bias andinputbiasmismatchingChoose ROUT to obtain the full-scale voltageyoucurrents.After selectingthe ratio,check toNote4:Printed CircuitDesign,by GeraldL.Ginsberg;McGraw-Hill,Inc.;page
185.require,given thefull-scale loUTdetermined byRSENSE,In orderto dissipatesense-resistor heatfrom largesenseRG1,and RG
2.The highcompliance ofOUT permitsusing currents,solder the RS+pins and the RS-pins tolargeROUT valuesupto10kQ withminimal error.Values abovecopper traces.Keep thepart awayfrom other10kQ arenot usuallyrecommended.The impedanceof heat-generating devices.This procedurewill ensureOUTsload e.g.,the inputof anop ampor ADCmust becontinuous power dissipation rating.much greaterthan ROUTe.g.,100x ROUTto avoiddegradingthe measurement accuracy.High-Current MeasurementThe MAX472can achievehigher currentmeasurementsthan the MAX471can.Low-value sense resistors may beparalleled toobtain evenlower values,or thePC boardtracemay be adjusted forany value.An alternativemethod isto connectseveral MAX471s inparalleland connectthe high-impedance currentsourceOUT pins togetherto indicatethetotalsystem currentFigure
3.Pay attentionto layoutto ensureequal IRdropsin theparalleled connection.This isnecessary to achieveequal current sharing.Power-Supply Bypassingand GroundingThe MAX471has beendesigned asa“high sidepositiveterminal currentmonitor toease thetask ofgrounding anybatterycharger,thermistor,etc.that maybeapartof thebattery pack.Grounding the MAX471requires nospecialprecautions;follow the same cautionarysteps thatapply tothesystem asa whole.High-current systemscanexperience largevoltage dropsacross aground plane,andthis dropmay addto orsubtract fromVoUT.For highestcurrent-measurementaccuracy,use asingle-point“star”ground.The MAX471/MAX472require nospecial bypassing,andrespond quicklyto transientchanges inline current.If thenoiseat OUTcaused bythese transientsis aproblem,youmay want to placea1pF capacitor at theOUTpinto ground.You can also placealargecapacitoratthe RS-terminal oruload^^sideof the MAX472to decouplethe loadand,thereby,reduce the current transients.These capacitorsarenot requiredfor MAX471/MAX472operation orstability,and theiruse willnot degradeperformance.For the MAX472,the RG1and RG2inputs canbe filteredbyplacing acapacitor e.g.,1pF betweenthem toaveragethe sensed current.MAX471LayoutThe MAX471must besoldered inplace,since socketscancause unevencurrentsharingbetweentheRS+pins pins2and3andtheRS-pins pins6and7,resulting intypicalerrors of
1.4WDifferential InputVoltage,RG1to RG2MAX472only…±
0.3V Voltageat SOderate
0.3V to RS+-
0.3V toVcc+
0.3V PlasticDIPderate
0.3V to+40V SOderate
472.RS+and RS-mustbesolderedto largecopper tracestoachievethis dissipationrating.Stressesbeyondthoselistedunder“AbsoluteMaximumRatingsmaycausepermanentdamagetothedevice.Thesearestressratingsonly,andfunctionaloperationofthedeviceattheseoranyotherconditionsbeyondthoseindicatedintheoperationalsectionsofthespecificationsisnotimplied.Exposuretoabsolutemaximumratingconditionsforextendedperiodsmayaffectdevicereliability.ELECTRICAL CHARACTERISTICS—MAX471RS+=+3V to+36V,TA=TMiNto TMAX,unless otherwisenoted.Typical valuesare atTA=+25℃.PARAMETER SYMBOLCONDITIONS MINTYP MAXUNITSSupply Voltage336VVRS+Supply Current IRS+ILOAD=0A,excludes ISIGN50113MASense CurrentILOAD±3ARMSSense ResistorRSENSE3570mQIOUT/ILOAD=1A,MAX471C
0.
4900.
5000.510Current-Sense RatiomA/AILOAD RS+=10V MAX471E
0.
48750.
5000.5125ILOAD=0A,M AX471C
2.5No-Load OUTError RS+=10V MAX471E
3.0pAILOAD=30mA,MAX471C±
2.5Low-Level OUTError RS+=10V MAX471E±
3.0MAPower-Supply RejectionRatio PSRR3VRS+36V,ILOAD=1A
0.1%/VMAX471C±
4.0±
6.0SIGN ThresholdILOAD required tomAswitch SIGNMAX471E±
7.0SIGN OutputLeakage CurrentVsiGN=36V
1.0MASIGN Sink Current IOLVsiGN=
0.3V
0.1mAShutdown SupplyCurrentIRS+SHDN VSHDN=
2.4V;Vcc=3V to20V
1.
518.0MASHDN InputLow VoltageVIL
0.3VSHDN InputLow CurrentIIL VSHDN=0V
1.0MASHDN InputHigh VoltageVIH
2.4VSHDN InputHigh CurrentIIH VSHDN=
2.4V
1.0MAOUT Output Voltage RangeVOUT0VRS+-
1.5VOUT OutputResistance ROUTILOAD=
3.0A,VOUT=0V toVRS+-
1.5V13MQOUT Rise,Fall TimetR,tF ILOAD=50mA to
3.0A,ROUT=2kQ,COUT=50pF,4MS10%to90%OUT SettlingTime to1%of Finalts15MSValue ILOAD=100mA to
3.0A,ROUT=2kQ,CoUT=50pFELECTRICAL CHARACTERISTICS—MAX472Vcc=+3Vto+36V,RG1=RG2=200Q,TA=TMlNto TMAX,unless otherwisenoted.Typical valuesare atTA=+25℃.PARAMETER SYMBOLCONDITIONS MINTYP MAXUNITSSupply Voltage336VVccSupply CurrentIcc ILOAD=OA,excludes ISIGN；VCC=3V to20V2048MAMAX472C120Input OffsetVoltage Note2Vos MVMAX472E140Input BiasCurrent IRG1,IRG22035MAInput Bias-Current Matchinglos±
0.4±
3.0IRG1-IGR2MAMAX472C±2VSENSE=lOOmV,OUT CurrentAccuracy IRG/IOUT VCC=10V Note3MAX472E±
2.5%Vcc=10V,VSENSE=MAX472C
2.5No-Load OUTError0VMAX472E3MAMAX472C±
2.5Wcc=10V,VSENSE=Low-Level OUTError3mV MAX472E±
3.0MAPower-Supply RejectionRatio PSRR%/v3VVcc36V,VSENSE=10OmV
0.1MAX472C60120SIGN ThresholdVSENSE requiredtoVcc=10Vswitch SIGNMAX472E60140MVSIGN OutputLeakage CurrentVsiGN=36V
1.0MASIGN OutputSinkCurrentVsiGN=
0.3V
0.1mAShutdown SupplyCurrent ICCSHDNVSHDN=
2.4V；Vcc=3V to20V
1.
518.0MASHDN InputLow VoltageVIL
0.3VSHDN InputLow CurrentIIL VSHDN=0V
1.0MASHDN InputHigh Voltage
2.4VVlHSHDN InputHigh CurrentVSHDN=
2.4V
1.0IlH MAOUTOutputVoltageRange0Vcc-
1.5VVOUTOUT OutputResistance ROUTIOUT=
1.5mA13MQ，VSENSE=5mV to150mV,ROUT=2kOUT Rise,Fall TimetR,tF4MSCOUT=50pF,10%to90%，OUT SettlingTime to1%of Finalts VSENSE=5mV to150mV,ROUT=2k15MSValue COUT=50pFMaximum OutputCurrent lOUT
1.5mANote2:Vos isdefined as the inputvoltage VSENSErequiredtogive minimumIOUT.Note3:VSENSE isthe voltageacross thesense resistor.__________________________________________TypicalOperating CharacteristicsTypical OperatingCircuit MAX471or circuit of Figure4,RG1=RG2=200Q,ROUT=2kQ MAX472,TA=+25℃,unless otherwisenoted.SUPPLYOJRR04Tvs.SHUgANOJRRBbvs.SUPPLYVDLTAGE SIGNTHRESHOLDvs.SUPRYV0LTA3ESUPPIYV0LTA3E
6542.5T A=-40℃60lX=+85℃T A=-40℃
32.0552℃
1.5T=+25I NQLA A-十50A11A-TQU
1.0A45T=+85℃0A℃T=-40AT A=+85℃
0.540-1350-2369121518212427303336369121518212427303336369121518212427303336VRs.fV VRSWVRS^VMAX471MAX471MAX471PGV\mSUPRYREJECT10NR/KT10NOgADOFFSEFCURRB^Tvs.WRORvs.UCADCURRB^IT vs.FRB3JBMCY
2.41540vs+=vsdoILQAD=1A
2.235i A-一qu LA LOADFROMRS-TORS+9V=0VTO
0.5V
2.0306cur
1.8OD A325W革F
1.6V=0VTO1VT A=+85℃020V5Q
1.4T=+25℃-315Al.Z-6V=0mVTO50mV
101.0-91LOAD FROMRS+TORS-A
0.8-12□
0.6-
1503691215182124273033360.
010.
101100.
010.101101001000POWER-SUPPLY FREQUENCYkHzVRS^V ILOADAMAX471MAX472ROTORS-RESISTANCEvs.NObQADOUTHJrSWRvs.MAX4727BVPSWURE由RORvs.SUPPLYVOLEAGESUPPLYVOUTGE
403.
01.10VRGI-VRG2=60mV,RG1=RG2=0Q RG1=RG2=200Q
382.5℃T=+
851.00A
362.0T=+85℃A
341.
50.90℃T\=+251A-T”V
321.0A•A-TUUA
0.
80300.5℃T=-40A
2800.70-40-20020406080369121518212427303336369121518212427303336℃TEMPERATUREVccV VccVTypicalOperatingCharacteristicscontinuedTypical OperatingCircuit MAX471or circuitof Figure4,RG1=RG2=200Q,ROUT=2kQ MAX472,TA=+25℃,unless otherwisenoted.MAX472CC=10V WX4711BWRvs.SBNBEWUTGE Evs.LC¥MDOJRRBMT%,SIGNPULL-UP=50k£21%
250.5VMAX47115v STORRJPDaW
0.4RG1-VR
3250.30-
50.2VRG2-VRG1-
150.1-
250.1110100100001310mA100mA1AVsENSE mVISENSEVLQ^D LOAD聃CURFSMT OJRRB^TMJJF5S0IGNMAX4710A OmAtolOOmATR10W0pSse/dsiviTI5500mm VA//dd iivv0A-lOOmAto+100mAM7RA1ZX0m40p7Bs1/4diTvl ACNSEl/5O/d0O imvm VA/d/id vh/V cc=10VF^xjr=2kn1%,SIGNPULL-UP=50kQ1%MAX4710ATO3A7TSNSWRKPCNSELD^DPIN1A/divNAMEMAX4721SHDN VDUT500mV/div\^-CN5V/div—RS+2N.C.10ps/div3RG1产ILCW=1A,Roi2k£l1%4GNDPin Description5SIGNFUNCTION—RS-Shutdown.Connect to ground fornormal operation.When high,supply current is lessthan5pA.6RG2Battery or power sideof the internal current-sense resistor.The u+n indicatesdirection offlow forSIGN outputonly.Connect pins2and3together atthe package.7VccNo Connect-no internalconnection8OUTGain Resistor.Connect tobattery sideof current-sense resistorthrough thegain resistor.Ground orBattery NegativeTerminalAn open-collector logicoutput.For the MAX471,a lowlevel indicatescurrent isflowing fromRS-to RS+.For theMAX472,a lowlevel indicatesa negativeVSENSE seeFigure
2.SIGN is high impedancewhen SHDNis high.Leave openif SIGNis notneeded.Loadside of theinternalcurrent-senseresistor.The indicatesdirectionofflowfor SIGNoutput only.Connect pins6and7together atthe package.Gain Resistor.Connect to load sideof current-sense resistorthrough thegain resistor.Power inputfor MAX
472.Connect to sense resistorRSENSE junctionwith RG
1.Current outputthat isproportional to the magnitudeofthesensed currentflowing throughRSENSE.A2kQ resistorfromthis pintogroundwill resultin a voltage equalto1V/Amp ofsensedcurrentin the MAX
471.through aresistor.In thiscase,amplifier A1is activeandDetailed Descriptionoutputcurrent loUTflows from theemitter ofQ
1.Since noThe MAX471and MAX472current-sense amplifierscurrent flowsthrough RG2Q2isoff,the negative input ofuniquetopology allowsa simpledesign toaccurately A1is equalto VsoilRCE-ILOAD xSENSE.Themonitor currentflow.TheMAX471/MAX472contain twoopen-loop gainof A1forces itspositive inputto essentiallyamplifiersoperating as shown in Figures1and
2.The thesame levelasthenegativeinput.Therefore,the dropbattery/loadcurrentflowsfromRS+to RS-or viceversa acrossRG1equals ILOAD X RSENSE.Jhen.since.加IQUTflows throughQ1and RGignorrng theextremelyough RSENSE.Current flowsthrough eitherRG1and Q1orRG2and Q2,depending onthe senseresistorcurrent lowoasecurrents,T0UT XRG1=1LOADXRSENSE,ordirection.Internal circuitry,not showninFigures1and2,prevents Q1and Q2from turningon atthesametime.TheMJJT10mV/divMAX472is identicaltothe MAX471,except thatRSENSEand gain-setting resistorsRG1and RG2are externalFigure
2.10ps/divTo analyzethe circuitof Figure1,assume thatcurrent flowsRfromRS+to RS-and thatOUT isconnected toGND2g1%IOUT=ILOADx RSENSE/RG1full-scale currentbeing sensed,RSENSE=thecurrent-senseresistor,ROUT=thevoltage-setting resistor,Current Outputand RG=thegain-setting resistorRG=RG1=RG
2.The output voltage equationfor the MAX471/MAX472isThe aboveequation canbe modifiedto determinethegiven below.In the MAX471,thecurrent-gain ratiohas^OUT requiredforaparticular full-scale range:been presetto500pA/A sothat anoutput resistorROUTof2kQ yields1V/A forafull-scale valueof+3V at±3A.ROUT=VOUTX RG/ILOADx RSENSEOther full-scale voltagescanbeset withdifferent ROUTFor theMAX471,this reducesto:values,but theoutputvoltagecanbeno greaterthan VRS+OUT-VOUT7vLOAD x500pA/A-
1.5V for theMAX471or VRG_-
1.5V fortheMAX
472.一OUTisa high-impedance current-source outputthat canbeVOUT=RSENSE xROUTX ILOAD/RG wnereconnected toother MAX471/MAX472OUT pinsVOUT=the desiredfull-scale outputvoltage,ILOAD=the6,7RS-Figure
1.MAX471Functional DiagramPCXAERSOURCEFG1RG2CRVSB^ERSI R2Figure
2.MAX472Functional DiagramA1QI C2A1OUTVC2OCOOVP SIGNOUTMW471OOMPSIGNMWI72R-RS-RTOLCmCHARGS^R-FS-FOAW3VMAX47LOGO93URCESIGN TOFG11SUFRY CR36VILR R32ourGND100k TOLOAOLOGICSUFRY3V100kTO36VMW472R-RS1ShCN cur8R-RS2N.C.Mx7RMAX473FG1FG26ourSIGN14GND SIGN5OUTVGhDOUT1kFigure
3.Paralleling MAX471stoSense Figure
4.MAX472Standard ApplicationCircuitHigher LoadCurrentfor currentsumming.A singlescaling resistor is requiredneeded,float theSIGN pin.when summingOUT currents from multipledevices FigureShutdown
3.Current canbe integratedby connectingOUTtoaWhen SHDNis high,theMAX471/MAX472are shutdowncapacitive load.and consumelessthan18pA.In shutdownmode,SIGN ishighimpedance andOUT turnsoff.SIGN OutputThecurrent atOUT indicatesmagnitude.The SIGNoutput ApplicationsInformationindicates thecurrents direction.Operation ofthe SIGNMAX471comparator isstraightforward.When Q1Figures1and2conducts,theoutputof A1ishighwhile A2,s outputis zero.TheMAX471obtains itspower fromtheRS-pin.Thisincludes MAX471current consumptionin thetotal systemUnderthis condition,a highSIGNoutputindicates positivecurrentmeasured bytheMAX
471.The smalldrop acrosscurrentflow fromRS+to RS-.In battery-operatedR$ENSE doesnotaffecttheMAX471s performance.systems,this is useful fordetermining whetherthe batteryischarging ordischarging.The SIGNoutput maynotResistor Selectioncorrectlyindicate ifthe loadcurrentissuch thatloUTis lessSinceOUT deliversacurrent,an externalvoltagethan
3.5pA.TheMAX471s SIGNoutput accuratelygainsettingresistor RoilTtoground isrequired atthe OUTindicatesthe directionof currentflow forload currentspinin orderto getavoltage.RSENSE isinternal tothegreater than7mA.MAX471,RG1and RG2are factorytrimmed foran outputSIGNis anopen-collector outputsinks currentonly,current ratiooutputcurrenttoloadcurrent of500pA/A.allowing easyinterface withlogic circuitspowered fromanySince theyare manufacturedofthesame materialand involtage.Connect a100kQ pull-up resistorfrom SIGNto theveryclose proximityonthechip,they providea highdegreelogic supply.The conventionchosen forthe polarityof theoftemperature stability.ChooseROUTforthedesiredSIGN outputensures thatit drawsno currentwhen thefull-scale outputvoltage uptoRS--
1.5V seethe Currentbatteryis beingdischarged.If currentdirection isnotOutput section.Peak SenseCurrent Table1shows suggestedcomponent valuesand indicatesTheMAX4715s maximumsense currentis3ARMS.Fortheresulting scalefactors forvarious applicationsrequiredpower-up,fault conditions,or otherinfrequent events,tosensecurrentsfrom100mA to10A.larger peakcurrents areallowed,provided theyareHigher orlower sense-current circuitscanalsobe built.short—that is,within asafe operatingregion,as showninSelect componentsand calculatecircuit errorsusing theFigure
5.guidelines andformulas inthe followingsection.50“SENSESm^l45DIP ChooseRSENSEbased onthe followingcriteria:Outlinefuse℃7A=+25fuse40time aVoltage Loss:A highRSENSE valuewill cause thetimepower-source voltageto degradethrough IRloss.For35least voltageloss,usethelowest RsENSEvalue.30飞25M n.yn ENSEvalue allowslowercurrents tobemeasuredmore accurately.This is20because offsetsbecome lesssignificant whenthesense15voltage islarger.10c Efficiencyand PowerDissipation:At highcurrentlevels,thel2R lossesin RSENSEmaybesignificant.Take thisinto considerationwhen choosingthe resistor10p100p1m10mvalue andpowerdissipationwattage rating.Also,if thePULSEWIDTHsecsenseresistorisallowed toheat upexcessively,itsDIPsafeoperating SmaiOutlinesafevaluemay drift.region operatingregionFigure
5.MAX471Pulse CurrentSafe Operationfor10,000Pulses andd Inductance:If thereisalarge high-frequencyFuse Timefor ContinuousCurrent.Pulse testsdone with250mW averagecomponentto IsENSE,you willwant tokeep inductancepowerdissipation.low.Wire-wound resistorshave thehighest inductance,while metalfilm issomewhat better.Low-inductancemetal-film resistorsare available.Instead ofbeing spiralMAX472wrapped arounda core,as inmetalfilm orwire-woundRSENSE,RG1,andRG2are externallyconnected ontheresistors,these area straightband ofmetal.They areMAX
472.Vcc canbe connectedtoeitherthe load/chargemade invalues under1Q.orpower-source/battery sideofthesenseresistor.ConnectVcc totheload/charge sideof RSENSEif youwanttoe Cost:If thecost ofRSENSE becomesan issue,youinclude theMAX472current draininthemeasured current.may wantto usean alternativesolution,asshowninFigure
6.This solutionuses thePC boardtraces toSuggested Component Valuescreatea senseresistor.Because ofthe inaccuraciesoffor VariousApplicationsthe copperresistor,n youwill needto adjusttheThe generalcircuitofFigure4isusefulin awide varietyoffull-scale currentvalue witha potentiometer.Also,theapplications.It canbe usedfor high-current applicationsresistancetemperature coefficientof copperis fairlygreaterthan3A,and alsofor thosewhere thefull-scale℃high approximately
0.4%/,so systemsthatload currentis lessthanthe3A oftheMAX
471.experience awide temperaturevariance shouldtakethis intoaccount.Table
1.SuggestedComponentValues fortheMAX472CURRENTSE SCALEFULL-SCALE GAIN-SETTING OUTPUTFULL-SCALE TYPICALERROR ATX%NSE FACTOR,LOAD RESISTORS,RG1RESISTOR,OUTPUT OFFULL LOAD%RESISTOR,VOUT/ISENSECURRENT,=RG2ROUT VOLTAGE,A//A\ISENSE AKSENSE mQkQ VOUTV V/AQ1%10%100%
0.
1500200102.
525142.
50.
9150200102.
52.
5142.
50.
951010052.
50.
5132.
01.
110550220.
2122.
01.6。
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