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Motor de Búsqueda de Datasheet de Componentes Electrónicos |
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SP7661 Datasheet(PDF) 9 Page - Sipex Corporation |
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SP7661 Datasheet(HTML) 9 Page - Sipex Corporation |
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9 / 20 page  9 Nov3-06 Rev I SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator © 2006 Sipex Corporation Error Amplifier and Voltage Loop TheheartoftheSP7661voltageerrorloop is a high performance, wide bandwidth transconductance amplifier. Because of theamplifier’scurrentlimited(+/-150µA) transconductance,therearemanywaysto compensatethevoltagelooportocontrolthe COMPpinexternally.Ifasimple,single-pole, single-zeroresponseisdesired,thencom- pensationcanbeassimpleasanRCcircuit toGround.Ifamorecomplexcompensation isrequired,thentheamplifierhasenough bandwidth(45°at4MHz),andenoughgain (60dB)torunTypeIIIcompensationschemes withadequategainandphasemarginsat crossoverfrequenciesgreaterthan50kHz. Thecommonmodeoutputoftheerroram- plifieris0.9Vto2.2V.Therefore,thePWM voltageramphasbeensetbetween1.1Vand 2.2Vtoensureproper0%to100%dutycycle capability. The voltage loop also includes twootherveryimportantfeatures.Oneisa nonsynchronousstartupmode.Basically,the synchronousrectifiercannotturnonunless thehighsideswitchhasattemptedtoturn onortheSSpinhasexceeded1.7V.This featurepreventsthecontrollerfrom“dragging down”theoutputvoltageduringstartupor infaultmodes. GH Voltage GL Voltage V(VIN) 0V -0V -V(Diode) V V(VIN)+V(VCC) BST Voltage V(VCC) TIME SWN Voltage VBST VSWN V(VCC) Thesecondfeatureisa100%dutycycle timeoutthatensuressynchronizedrefresh- ingoftheBSTcapacitoratveryhighduty ratios.IntheeventthatthehighsideNFET isonfor20continuousclockcycles,areset isgiventothePWMflipflophalfwaythrough the21stcycle.ThisforcesGLtoriseforthe cycle,inturnrefreshingtheBSTcapacitor. Theboostcapacitorisusedtogeneratea highvoltagedrivesupplyforthehighside switch,whichisVccaboveViN. Power MOSFETs TheSP7661containsapairofintegratedlow resistanceN-channelswitchesdesignedto driveupto3Aofoutputcurrent.Careshould betakentode-ratetheoutputcurrentbased onthethermalconditionsinthesystemsuch as ambient temperature, airflow and heat sinking.Maximumoutputcurrentcouldbe limitedbythermallimitationsofaparticular applicationbytakingadvantageoftheinte- grated-over-temperatureprotectivescheme employedintheSP7661.TheSP7661incor- poratesabuilt-inovertemperature protection topreventinternaloverheating. Setting Output Voltages TheSP7661canbesettodifferentoutput voltages.Therelationshipinthefollowing formulaisbasedonavoltagedividerfrom theoutputtothefeedbackpinVfB,whichis settoaninternalreferencevoltageof0.80V. Standard1%metalfilmresistorsofsurface mountsize0603arerecommended. VOut=0.80V [R1/R2+1] => R2=R1/ [ (VOut/0.80V)–1] WhereR1=10KΩandforVOut=0.80V setting,simplyremoveR2fromtheboard. Furthermore,onecouldselectthevalueof theR1andR2combinationtomeettheexact outputvoltagesettingbyrestrictingtheR1 resistance range such that 10KΩ < R1 < 100KΩforoverallsystemloopstability. APPLICATIONS INFORMATION |
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