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HT7963 数据表(PDF) 4 Page - Holtek Semiconductor Inc |
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HT7963 数据表(HTML) 4 Page - Holtek Semiconductor Inc |
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4 / 11 page  Rev. 1.00 4 August 14, 2015 HT7963 Symbol Parameter Test Condition Min. Typ. Max. Unit THSHD_HYS Hysteretic Temperature — — 30 — °C LED Output Current VFB Current Feedback Sensing Voltage VFB — 0.3 — V ERRFB Tolerance of VFB — -3.0 — +3.0 % DIM IOUT 50ms, TSHD Shutdowm mode 30ms TRT Figure1 Functional Description General Operation ThedeviceisanLEDdriveroperatingasaDC- DCboostconverterinaconstantfrequencymode. Itimplementsapeakcurrentmodecontrolandhas aninternalamplifiertoaccuratelycontroltheoutput currentoverconditionsofwideinputvoltageand varyingload. Soft Start – SS Thedevicehasdedicatedprotectioncircuitryrunning duringnormaloperation.TheSoftStartfunctionis settohaveaninternaltimeofaround5msandisused topreventalargeinrushcurrentduringthepower-on period. Output Gate Drive Stage ACMOSbufferoutputstageisincludedtodrive apowerMOSFETdirectly.Theoutputvoltageis clampedat13VtoprotecttheMOSFETgateeven whentheVCCvoltageishigherthan13V. Input Under Voltage Lockout – UVLO Thedevicecontainsaninputunder-voltagelockout circuit.ThepurposeoftheUVLOcircuitistoensure thattheinputvoltageishighenoughforreliableop- eration.Whentheinputvoltagefallsbelowtheunder voltagethreshold,theexternalFETswitchisswitched off.Iftheinputvoltagerisesbeyondtheundervolt- beyondtheundervolt- theundervolt- agelockouthysteresisvalue,thedevicewillrestart. TheUVLOthresholdissetbelowtheminimuminput voltageof6VtoavoidanytransientVINdropsunder theUVLOthresholdwhichmaycausetheconverter toswitchoff. Current Limiting Thedevicehasacycle-by-cyclecurrentlimittoprotect theexternalpowerMOSFET.Iftheinductorcurrent reachesthecurrentlimitthreshold,whichiswhen theCSpinvoltageisgreaterthan0.5V,theexternal MOSFETwillbeswitchedoff.TheRcsvaluecanbe calculatedfromthefollowingformula: ILIMIT=0.5V RCS Dimming Control TheLEDbrightnesscontrolisimplementedusinga PWMsignalontheDIMpin.ThePWMdutycycle isproportionaltothedimmingvalue.Thedevice canapplyanexternalPWMsignalontheDIMpin withafrequencyrangefrom100Hzto1kHzwiththe requiredhigh/lowratio. Output Over Voltage Protection – OVP Thedeviceincludesanover-voltageprotectionfunc- includesanover-voltageprotectionfunc- anover-voltageprotectionfunc- over-voltageprotectionfunc- over-voltageprotectionfunc- tion.Inabnormalconditions,theoutputvoltagemay exceeditsmaximumvoltagerating,possiblydamag- ingexternalcomponentsandtheLEDs.Protection circuitryturnsoffthepowerMOSFETandshuts downthedeviceassoonastheoutputvoltageexceeds theVOVPthreshold.Asaresult,theoutputvoltagefalls totheleveloftheinputsupplyvoltage.Thedevice remainsintheshutdownmodeuntilthepowerisre- theshutdownmodeuntilthepowerisre- shutdownmodeuntilthepowerisre- cycled.TheVOUT_OVPvaluecanbecalculatedfromthe followingformula: VOUT_OVP=1.938V×R 1 +R2 R2 Output Short Protection – OSP Anoutputshortconditionisdetectedbythevoltage onpinOVP.Intheperiodduringthefault,ifthe voltageontheOVPpindropsbylessthanathreshold ofaround0.1V,thentheoutputshortprotectionwill beactivatedandthepowerMOSFETwillbeswitched off. |
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