LTC4257

LTC425714257fbTheLTC®4257providescompletesignatureandpowerinterfacefunctionsforadeviceoperatinginanIEEE802.3afPoweroverEthernet(PoE)system.TheLTC4257simplifiesPoweredDevice(PD)designbyincorporatingthe25ksignatureresistor,theclassificationcurrentsource,inputcurrentlimitwiththermalfoldback,undervoltagelockoutandpowergoodsignalling,allinasingle8-pinpackage.ByincorporatingahighvoltagepowerMOSFETonboard,theLTC4257providesthesystemdesignerwithreducedcostwhilealsosavingboardspace.TheLTC4257caninterfacedirectlywithavarietyofLinearTechnologyDC/DCconverterproductstoprovideacosteffectivepowersolutionforIPphones,wirelessaccesspointsandotherPDs.LinearTechnologyalsoprovidessolutionsforPowerSourcingEquipment(PSE)applica-tionswithquadnetworkpowercontrollers.TheLTC4257isavailableinthe8-pinSOandlowprofile(3mm×3mm)DFNpackages.■IPPhonePowerManagement■WirelessAccessPoints■TelecomPowerControl,LTCandLTareregisteredtrademarksofLinearTechnologyCorporation.■CompletePowerInterfacePortforIEEE802.3af®PoweredDevices(PDs)■Onboard100V,400mAPowerMOSFET■PrecisionInputCurrentLimit■Onboard25kSignatureResistor■ProgrammableClassificationCurrent(Class0-4)■UndervoltageLockout■SmartThermalProtection■PowerGoodSignal■Availablein8-PinSOandLowProfile(3mm×3mm)DFNPackagesIEEE802.3afPDPoweroverEthernetInterfaceControllerGNDRCLASSRCLASSSMAJ58A0.1µFPWRGDLTC4257VINSHDN5µFMIN100k3.3VTOLOGICRTNSWITCHINGPOWERSUPPLYVINVOUT–48VFROMPOWERSOURCINGEQUIPMENT(PSE)4257TA01+–+DF01SA~~+–PoweredDevice(PD)5ms/DIVVIN50V/DIVVOUT20V/DIVIIN200mA/DIVPWRGD50V/DIV4225TA02LTC4257Charging300µFLoadCapacitorFEATURESDESCRIPTIOUAPPLICATIOSUTYPICALAPPLICATIOUAllothertrademarksarethepropertyoftheirrespectiveowners.LTC425724257fbTOPVIEWDDPACKAGE8-LEAD(3mm×3mm)PLASTICDFN56784321NCRCLASSNCVINGNDNCPWRGDVOUTSYMBOLPARAMETERCONDITIONSMINTYPMAXUNITSVINSupplyVoltageVoltagewithRespecttoGNDPin(Notes4,5,6)MaximumOperatingVoltage●–57VSignatureRange●–1.5–9.5VClassificationRange●–12.5–21VUVLOTurn-OnVoltage●–37.7–39.2–40.2VUVLOTurn-OffVoltage●–29.3–30.5–31.5VIIN_ONICSupplyCurrentwhenONVIN=–48V,Pins5,6Floating●3mAIIN_CLASSICSupplyCurrentDuringClassificationVIN=–17.5V,Pin2Floating,VOUTTiedtoGND●0.350.500.65mA(Note7)∆ICLASSCurrentAccuracyDuringClassification10mAICLASS40mA,–12.5V≤VIN≤–21V,●±3.5%(Notes8,9)(Notes1,2)VINVoltage.............................................0.3Vto–100VVOUT,PWRGDVoltage.............VIN+100VtoVIN–0.3VRCLASSVoltage............................VIN+7VtoVIN–0.3VPWRGDCurrent..................................................10mARCLASSCurrent..................................................100mAThe●denotesthespecificationswhichapplyoverthefulloperatingtemperaturerange,otherwisespecificationsareatTA=25°C.(Note3)ABSOLUTEAXIURATIGS°Cto70°CLTC4257I.............................................–40°Cto85°CStorageTemperatureRangeS8Package.......................................–65°Cto150°CDDPackage......................................–65°Cto125°CLeadTemperature(Soldering,10sec)..................300°CConsultLTCMarketingforpartsspecifiedwithwideroperatingtemperatureranges.*Thetemperaturegradesareidentifiedbyalabelontheshippingcontainer.ORDERPARTNUMBERS8PARTMARKINGTJMAX=150°C,θJA=150°C/W42574257ILTC4257CS8LTC4257IS812348765TOPVIEWGNDNCPWRGDVOUTNCRCLASSNCVINS8PACKAGE8-LEADPLASTICSOPACKAGE/ORDERIFORATIOUUWORDERPARTNUMBERDDPARTMARKING*TJMAX=125°C,θJA=43°C/WEXPOSEDPADTOBESOLDEREDTOELECTRICALLYISOLATEDPCBHEATSINKLACTLTC4257CDDLTC4257IDDOrderOptionsTapeandReel:Add#TRLeadFree:Add#PBFLeadFreeTapeandReel:Add#TRPBFLeadFreePartMarking:●denotesthespecificationswhichapplyoverthefulloperatingtemperaturerange,otherwisespecificationsareatTA=25°C.(Note3)Note1:StressesbeyondthoselistedunderAbsoluteMaximumRatingsmaycausepermanentdamagetothedevice.ExposuretoanyAbsoluteMaximumRatingconditionforextendedperiodsmayaffectdevicereliabilityandlifetime.Note2:AllvoltagesarewithrespecttoGNDpin.Note3:TheLTC4257operateswithanegativesupplyvoltageintherangeof–1.5Vto–57V.Toavoidconfusion,voltagesinthisdatasheetarealwaysreferredtointermsofabsolutemagnitude.Termssuchas“maximumnegativevoltage”refertothelargestnegativevoltageanda“risingnegativevoltage”referstoavoltagethatisbecomingmorenegative.Note4:TheLTC4257isdesignedtoworkwithtwopolarityprotectiondiodesbetweenthePSEandPD.ParameterrangesspecifiedintheElectricalCharacteristicsarewithrespecttoLTC4257pinsandaredesignedtomeetIEEE802.3afspecificationswhenthesediodedropsareincluded.SeeApplicationsInformation.Note5:Signatureresistanceismeasuredviathe2-point∆V/∆ImethodasdefinedbyIEEE802.3af.TheLTC4257signatureresistanceisoffsetfrom25ktoaccountfordioderesistance.Withtwoseriesdiodes,thetotalPDresistancewillbebetween23.75kand26.25kandmeetIEEE802.3afspecifications.TheminimumprobevoltagesmeasuredattheLTC4257pinsare–1.5Vand–2.5V.Themaximumprobevoltagesare–8.5Vand–9.5V.Note6:TheLTC4257includeshyste