SM74611 Smart Bypass Diode (Rev. B) - TI.com

1 SM74611SM74611SM74611PV (-)PV (+)KAAAKKJUNCTION BOXPV MODULEC opyright 2016, Texas Instruments IncorporatedProductFolderSample &BuyTechnicalDocumentsTools &SoftwareSupport &CommunityReferenceDesignAn IMPORTANTNOTICEat the end of this datasheetaddressesavailability,warranty, changes,use in safety-criticalapplications,intellectual propertymattersand DECEMBER2012 REVISEDMAY2016SM74611 SmartBypassDiode11 Features1 MaximumReverseVoltage(VR) of 30 V OperatingForwardCurrent(IF) of up to 15 A Low AverageForwardVoltage(26 mV at 8 A) LessPowerDissipationthanSchottkyDiode LowerLeakageCurrentthanSchottkyDiode Footprintand Pin-CompatibleWithConventionalD2 PAKS chottkyDiode OperatingRange(TJ) of 40 C to 125 C2 Applications BypassDiodesfor PhotovoltaicPanels BypassDiodesfor Microinverterand PowerOptimizer3 DescriptionThe SM74611deviceis a purposeof providingan alternatepathforstringcurrentwhenpartsof the panelare ,theshadedcellswill exhibita hot spot whichis causedbyexcessivepowerdissipationin the ,conventionalP-NjunctiondiodesorSchottky diodesare usedto forwardvoltagedropfor thesediodesis still consideredhigh( Vfor normaldiodesand V for Schottky).

2 With10 Aof currentsflowingthroughthesediodes,the powerdissipationcan reachas high as 6 W. This in turn willraisethe temperatureinsidethe junctionbox advantageof the SM74611is that it has a lowerforwardvoltagedropthanP-N junctionand has a typicalaverageforwardvoltagedropof 26 mV at 8 A of translatesinto typicalpowerdissipationof 208 mW,whichis significantlylowerthanthe W of alsofootprintandpin compatiblewith conventionalD2 PAKS chottkydiodes,makingita drop-inreplacementin (1)PARTNUMBERPACKAGEBODYSIZE(NOM) SM74611 TO-263(3) (1) For all availablepackages,see the orderableaddendumatthe end of the a JunctionBox2SM74611 SNVS903B DECEMBER2012 : SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporatedTableof Contents1 Pin Configurationand Applicationand Deviceand Mechanical,Packaging,and RevisionHistoryChangesfromRevisionA (November2014)to RevisionBPage AddedDeviceFunctionalModes,Applicationan d Implementationsection,PowerSupplyRecomme ndationssection,Layoutsection,Deviceand DocumentationSupportsection,andMechanica l,Packaging,and (December2012)to RevisionAPage Addednew junctiontemperaturefor t 1 DECEMBER2012 REVISEDMAY2016 ProductFolderLinks: SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporated(1)Pin 1 and Pin 3 mustbe connectedtogetherfor properoperation.

3 (2)Packagedrawingat the end of datasheetis shownwithoutPin 2 Pin Configurationand FunctionsKTTP ackage3-PinTO-263 Top ViewPin (1)IConnectbothof thesepins to the negativeside of the PV cells3(1)CATHODE2(2)OPin 2 and the DAPare DAPto the positiveside of the PV cellsDAP(2)(1)Stressesbeyondthoselistedu nderAbsoluteMaximumRatingsmay causepermanentdamageto the stressratingsonly,whichdo not implyfunctionaloperationof the deviceat theseor any otherconditionsbeyondthoseindicatedunder RecommendedOperatingConditions. Exposureto absolute-maximum-ratedconditionsfor extendedperiodsmay affectdevicereliability.(2)Systemmustbe thermallymanagedso as not to exceedmaximumjunctiontemperature6 (unlessotherwisenoted)(1)(2)MINMAXUNITDC reversevoltage30 VForwardcurrent24 AJunctiontemperature,t 1 hour135 CStoragetemperature,Tstg 65125 C4SM74611 SNVS903B DECEMBER2012 : SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporated(1)JEDE C documentJEP155statesthat 500-VHBM allowssafe manufacturingwith a 1000V may actuallyhavehigherperformance.

4 (2)JEDEC documentJEP157statesthat 250-VCDM allowssafe manufacturingwith a 250 Vmay (ESD)ElectrostaticdischargeHuman-bodymod el(HBM),per ANSI/ESDA/JEDECJS-001(1) 1000 VCharged-devicemodel(CDM),per JEDEC specificationJESD22-C101(2) 250(1)Systemmustbe thermallymanagedso as not to (unlessotherwisenoted)(1)MINMAXUNITDC reversevoltage28 VJunctiontemperature(TJ) 40125 CForwardcurrent015A(1)For moreinformationabouttraditionaland new thermalmetrics,see theSemiconductorand IC PackageThermalMetricsapplicationreport, (1) SM74611 UNITKTT(TO-263)3 PINSR C/WR JC(top)Junction-to-case(top) C/WR C/W C/W C/WR JC(bot)Junction-to-case(bottom) C/W(1)Limits 40 C to 125 C applyoverthe entirejunctiontemperaturerangefor normaltype applyfor TA= TJ= 25 (AVG)Forwardcurrent815 AVF(AVG)ForwardvoltageIF= 8 ATJ= 25 C26mVPDP owerdissipationIF= 8 ATJ= 25 C208mWTJ= 125 C450 40 C to 125 C(1)575IF= 15 ATJ= 25 C695TJ= 125 C1389 DDutycycleIF= 8 ATJ= 25 125 28 VTJ= 25 ATJ= 125 1 10 0 5 10 15 20 25 30 REVERSE CURRENT ( A) REVERSE VOLTAGE (V) 125 C 85 C 25 C -40 C C002 Current (A)Average Forward Voltage (mV)024681012141618202224 26020406080100120140C003125 C85 C25 C-40 CCurrent (A)Power Dissipation (W)024681012141618202224 C85 C25 C-40 DECEMBER2012 REVISEDMAY2016 ProductFolderLinks: SM74611 SubmitDocumentationFeedbackCopyright 2012 2016, AverageForwardVoltage(Anodeto Cathode)OverTemperatureFigure2.

5 PowerDissipationOverTemperatureFigure3. ReverseCurrentOverTemperature(Cathodeto Anode)Controllerand FETD riverChargePumpANODECATHODEQ1C1 IBYPASSVFC opyright 2016, Texas Instruments Incorporated6SM74611 SNVS903B DECEMBER2012 : SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporated7 SM74611is designedfor use as a bypassdiodein SM74611usesa chargepumpto drivean N-channelFET to providea resistivepathfor the bypasscurrentto operationaldescriptionis describedin the Figure4 and t1 Whencellsin the solarpanelsare shaded,the FETQ1 is off and the bypasscurrentflowsthroughthe bodydiodeof the FETas shownon Figure4. Thiscurrentproducesa voltagedrop(VF) acrossANODEandCATHODE terminalof the time,the chargepumpcircuitryis activeand chargingcapacitorC1 to a t1 Oncethe voltageon the capacitorreachesits predeterminedvoltagelevel,the chargepumpis disabledand thecapacitorvoltageis usedto drivethe FET throughthe FET t2 Whenthe FET is active,it providesa low resistivepathfor the bypasscurrentto flow thus minimizingthe powerdissipationacrossANODEand FETis active,the voltageacrossthe ANODEandCATHODEis too low to operatethe time,the storedchargeon C1 is usedto supplythe controlleras well as drivethe t2 Whenthe voltageon the capacitorC1 reachesits predeterminedlowerlevel,the FETdrivershutsoff the bypasscurrentwill thenbeginto flowthroughthe bodydiodeof the FET,causingthe FETbodydiodevoltagedropof V to appearacrossANODEand chargepumpcircuitryis re-activatedand beginschargingthe capacitorC1.

6 Thiscyclerepeatsuntil the shadeon the panelis removedandthe stringcurrentbeginsto flow throughthe PV cellsinsteadof the bodydiodeof the DECEMBER2012 REVISEDMAY2016 ProductFolderLinks: SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporatedFeature Description(continued)The key factorto minimizingthe powerdissipationon the deviceis to keepthe FET on at a high duty thenbe reducedto a muchlowervoltagethanfor a Schottkyor ANODEto CATHODEV oltage(Ch1)WithIBYPASS= 15 A (Ch4)for SM74611in JunctionBox at85 C Q1 OFFI nitially,the internalFET Q1 is is betweent0and t1as shownin Figure5. WhencurrentbeginsflowingfromANODEto CATHODE,the FET Q1 bodydiodeconductswith a Q1 ONThe FETQ1 is ON betweent1and t2as shownin Figure5. Duringthis time,the FETgateis drivenand currentflowsthroughthe FET througha low (-)PV (+)KAAAKKJUNCTION BOXPV MODULEC opyright 2016, Texas Instruments Incorporated8SM74611 SNVS903B DECEMBER2012.

7 SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporated8 Applicationand ImplementationNOTEI nformationin the followingapplicationssectionsis not partof the TI componentspecification,and TI doesnot warrantits accuracyor s customersareresponsiblefor determiningsuitabilityof componentsfor test theirdesignimplementationto SM74611smartbypassdiodeis a drop-inreplacementfor traditionalbypassdiodesusedin photovoltaic(PV) a typicaldiode,whichhas a ,the SM74611dissipatessignificantlyless powerand allowsPV applicationssuchas solarjunctionboxesto applicationdiagramshownin Figure6 shows3 SM74611 SmartBypassDiodesconnectedin series,eachprovidinga bypasspathfor 8 solarcellsfor a total of 24 DECEMBER2012 REVISEDMAY2016 ProductFolderLinks: SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporatedTypical Application(continued) lists the parametersfor Figure6 Table1.

8 DesignParametersPARAMETEREXAMPLEVALUEM inimuminputvoltageVINMIN1 VMaximuminputvoltageVINMAX28 VMaximumforwardcurrentIMAX20 AJunctiontemperaturerangeTJ 40 C to 125 SM74611is primarilyusedin solarjunctionboxesto improvethe efficiencycomparedto commonlyusedP-N junctionor junctionboxeshave2 or 3 diodesin seriesconnectedacrossthe solarpanel,eachdiodeconnectedacrossa substringof solarcells,as shownin Figure6. Standardbodieslike IEC and ULmandatecertainthermaltestsfor bypassdiodesin the timeof this writing,the applicablespecificationsincludeIEC61215, IEC61646,EN 50548,IEC62790,and test proceduresacrossthesespecificationsare similarand includethe following: Applytemperatureprobeto the Diode (in the caseof SM74611the smartbypassdiode)body Apply75 50 C to the junctionbox, containingthe 2 to 3 (smartbypass)diodes Applypanel-rated,short-circuitcurrentthr oughthe box for 1 hour Increasethe currentto ratedvalueand continuetestingfor another1 hourWhilethe specificationsmaynot specifyhow the temperaturemustbe maintained,it is expectedthat therewillbe no air flowas in a real applicationbehinda no specificationof howthetemperatureis raisedfromroomto 750 C.

9 TI recommendsa gradualand controlledincreaseto avoidshocktothe productundertest. Usinga goodclimatechamberor ovenis neededto ensureuniformityand consistencyoftemperatureduringtest and fromtest of one junctionbox to also necessarywiththe thermocouplesand temperatureprobesusedduringthe is a goodidea to checkthe equipmentusedwith the junctionbox shouldbe to bodydiodepulses,asimplediodetestercannot be usedto test the exampletestingschemeis showninApplicationCurve. To avoidcomponentfailure,the SmartBypassDiodejunctiontemperaturemustn ot exceedthe the junctiontemperatureis calculatedbasedon the measuredvaluesfromthe temperatureprobecouldbe appliedon the top (plasticcase)or bottom(tab)of the SM74611body,asshownin Figure7. Methodsof applyingthis probevary fromKaptontape,2K-resins(for top) to soldering(bottomtab).It is goodto checkwith the certificationbodyregardingthe TemperatureProbeAttachmentDuringThermalT est10 VAR10 VS1 IfIrSM74611SM74611SM74611 VGND12+ 10SM74611 SNVS903B DECEMBER2012 : SM74611 SubmitDocumentationFeedbackCopyright 2012 2016,TexasInstrumentsIncorporatedBecause the SM74611 SmartBypassDiodecyclesthe FETON andOFFto rechargethe chargepump,occasionallythe bodydiodeconductsinsteadof the dropacrossthe SmartBypassDiodeisnot constantevenat to this switchingbehavior,a normaldiodetestercan not be usedto testthe operationof the followingtest schemeis provided,as an example,with junctionbox Figure8 whilereadingthe followingtest steps:Figure8.

10 ExampleTestSetupfor SM74611 Step1:TestingForwardvoltagedrop(set R suchthat If => 1 A) ToggleS1 to position1 Makesureto seeIfreadingof 10V/R MeasureVoltageacross3 SM74611or 1 ea SM74611 If the setupis workingproperly,Vf will be less than150 mV (Rdsonlosses)PotentialFaultConditions SM74611 FET is not turningON -> the measuredvoltagewill be > 500 mV SM74611deviceis not solderedand open-> NoIfcurrentis seenStep2:TestingReversevoltageturn OFF ToggleS1 to position2 MeasurecurrentIrwhichis expectedto be < 1 APotentialFaultConditions SM74611 FETis shortedor boardshortis present,the measuredcurrentIris sameasIfbut with reversepolarity.(Thisis only in the caseof testingeachSM74611and not applicablefor testing3 together). DECEMBER2012 REVISEDMAY2016 ProductFolderLinks: SM74611 SubmitDocumentationFeedbackCopyright 2012 2016, Start-UpRelatedto InputVoltagefromthe Panel9 PowerSupplyRecommendationsThe SM74611is designedto be implementedas bypassdiodein the voltagelevelfromsolarmodulesdoesnot exceed28 V.