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SP7661
Wide Input Voltage Range 3A, 600kHz, Buck Regulator
FEATURES
SP7661
DFN PACKAGE 7mm x 4mm (Option 2) LX 26 LX 25 LX 24 LX 23 VCC 22 Pin 27 1 BOTTOM VIEW Heatsink Pad 1 Connect to Lx 2 3 4 5 6 7 Heatsink Pad 2 Connect to GND Pin 28 Heatsink Pad 3 Connect to VINP Pin 29 8 9 PGND PGND PGND PGND GND VFB COMP SS GND
PowerBlox
TM
4.75Vto22VInputVoltageRangeusingSingleSupply 3Vto22VInputVoltageRangeusingDualSupply 1%0.8VReference 3AOutputCapability CurrentLimitingusingInductorDCR BuiltinLowRDS(ON) PowerSwitches 600kHzFixedFrequencyOperation OverTemperatureProtection ShortCircuitProtectionwithAuto-Restart WideBWAmpAllowsTypeIIorIIICompensation ProgrammableSoftStart FastTransientResponse HighEfficiency:Greaterthan93%Possible NonsynchronousStart-UpintoaPre-ChargedOutput AvailableinRoHSCompliant,LeadFreePackaging: Small7mmx4mmDFN U.S.Patent#6,922,041
UVIN 21 GND 20 GND 19 VIN 18 BST 17 LX 16 LX 15 LX 14
10 ISN 11 ISP 12 SWN 13 VINP
DESCRIPTION
TheSP7661isasynchronousstep-downswitchingregulatoroptimizedforhighefficiency.Thepartisdesigned forusewithasingle4.75Vto22Vsinglesupplyor3Vto22VinputifanexternalVccisprovided.TheSP7661 providesafullyintegratedbuckregulatorsolutionusingafixed600kHzfrequency,PWMvoltagemodearchitecture. ProtectionfeaturesincludeUVLO,thermalshutdown,outputcurrentlimitandshortcircuitprotection.TheSP7661 isavailableinthespacesavingDFNpackage.
TYPICAL APPLICATION CIRCUIT
VOUT 3.30V, 0-3A
3
VIN

12V (9.6V-22V)
C2 22uF C 22uF
28 27
LX
L1,Wurth-744311220 2.2uH,14mOhm,7x7mm,9A R3 5.11k C4 47nF R9
ISP
GNDPAD
GND
VFB 2 3 4 5 6 PGND PGND PGND PGND GND VFB COMP SS GND ISN ISP
SWNPAD
2
R4 5.11k
LX LX
26 25 24 23 22 2 20 19 18 7 6 15 14 NC
61.9k
ISN
C5 100uF RZ3 400
4
CZ2 6800pF
RZ2 4.02k
U1 SP7661
LX LX VCC UVIN GND GND VIN BST LX
CVCC 4.7uF CZ3 1500pF
VFB
R 0k
GND
CP 56pF CSS 47nF
7 8 9 0
CF1 100pF
R2 3.16k
VINPAD
C9 6.8nF
ISN ISP LX
2 3
SWN VIN
LX LX
SD101AWS DBST 22nF CBST
29
LX
Rs2 1Ohm
Cs2 2.2nF
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
ABSOLUTE MAXIMUM RATINGS
Thesearestressratingsonlyandfunctionaloperationofthedeviceattheseratingsoranyotherabovethoseindicatedintheoperationsections ofthespecificationsbelowisnotimplied.Exposuretoabsolutemaximumratingconditionsforextendedperiodsoftimemayaffectreliability. VCC...................................................................................................7V ViN.................................................................................................25V BST............................................................................................... 30V . LX-BST...............................................................................-0.3Vto7V LX........................................................................................-V to 30V Allotherpins ......................................................... -0.3VtoVCC +0.3V . StorageTemperature .................................................. -65Cto150C . PowerDissipation .......................................InternallyLimitedviaOTP . LeadTemperature(Soldering,10sec).......................................300C ESDRating .......................................................................... 2kV HBM . ThermalResistanceJC........................................................... 5C/W
SpecificationsareforTAMB =TJ =25C,andthosedenotedbyapplyoverthefulloperatingrange,-40CELECTRICAL SPECIFICATIONS
PARAMETER
QUIESCENT CURRENT ViNSupplyCurrent (Noswitching) ViNSupplyCurrent (switching) BSTSupplyCurrent (Noswitching) BSTSupplyCurrent (switching) PROTECTION: UVLO
MIN
TYP
1.5 8 0.2 3
MAX UNITS
3.0 14 0.4 6 mA mA
CONDITIONS
VfB=0.9V
mA mA
VfB=0.9V
VccUVLOStartThreshold 4.00 VccUVLOHysteresis UVINStartThreshold UVINHysteresis UVINInputCurrent 00 2.30 200
4.25 200 2.50 300
4.50 300 2.65 400 1.0
V mV V

mV A
UVIN=3.0V 2XGainConfig.,Measure VfB;Vcc=5V
ERROR AMPLIFIER REFERENCE ErrorAmplifierReference 0.792 0.800 0.808 0.784 0.800 0.816 70 -230 150 -150 50 3.2 3.5 -2.0 230 -70 200 3.8 V V
ErrorAmplifier ReferenceOverLine COMPSinkCurrent COMPSourceCurrent VfBInputBiasCurrent COMPClamp COMPClampTemp. Coefficient
VCC LINEAR REGULATOR

VfB=0.9V,COMP=0.9V VfB=0.9V,COMP=0.9V VfB=0.8V VfB=0.7V,TA=25C
A A
nA V mV/C
VCCOutputVoltage
4.7 4.51 250
5.0 4.73 500
5.3
V
DropoutVoltage
Mar -07 Rev N
750
mV
ViN = 6 to 23V, ILOAD=0mAto30mA ViN=5V,20mA Vin-Vout=Dropoutvoltagewhen Vccregulateddropsby2%. IVCC=30mA.
(c) 2007 Sipex Corporation
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
2
SpecificationsareforTAMB =TJ =25C,andthosedenotedbyapplyoverthefulloperatingrange,-40CELECTRICAL SPECIFICATIONS
PARAMETER
RampAmplitude RAMPOffset RampoffsetTemperature Coefficient GHMinimumPulseWidth MaximumControllable DutyRatio MaximumDutyRatio InternalOscillatorRatio TIMERS: SOFTSTART SSChargeCurrent: SSDischargeCurrent: ShortCircuitThreshold Voltage
MIN TYP MAX UNITS
0.80 1.7 1.00 2.0 -2 150 92 00 510 -6 1.0 600 -0 2.0 690 -4.0 3.0 97 180 1.20 2.3 V V mV/C ns % % kHZ
CONDITIONS
CONTROL LOOP: PWM COMPARATOR, RAMP & LOOP DELAY PATH

FaultPresent, SS=0.2V Validfor20cycles
A
mA
PROTECTION: SHORT CIRCUIT, OVERCURRENT & THERMAL 0.2 90 54 0 135 145 135 0 0.25 0 60 0.3 30 V ms mV

VfB=0.5V MeasuredISP-ISN
HiccupTimeout OvercurrentThreshold Voltage ISP,ISNCommonMode Range ThermalShutdown Temperature ThermalRecovery Temperature ThermalHysteresis
OUTPUT: POWER STAGE
66
3.6 155
V C C C
VGS=4.5V; IDrAiN=4.1A; TAMB=25C VGS=4.5V; IDrAiN=4.1A; TAMB=25C Guaranteedbydesign
HighSideSwitchRDSON SynchronousLowSide SwitchRDSON MaximumOutput Current
Mar -07 Rev N
35
75
m
35 3
75
m A
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
3
CONTROLLER BLOCK DIAGRAM
VC C
C OMP SS V FB INT 1.6 V
A S Y NC . S TAR TUP C OMP A R A TOR GL HOLD OFF BS T
V FB VCC 10 uA S OFTS TA R T INP UT SS 0.1V
P W M LO O P
VC C Gm ER R OR A MP LIFIE R FA ULT RE S E T DOMINA NT R Q P OS R E F FAULT S QP W M
GH
VPOS
Gm
S Y NC HR O NO US DR I V E R
S WN GL
FA ULT
600 kHZ P GN D C LK C LOC K P ULS E GEN E R A TOR 2.8 V 1.3 V FAULT
R AMP =1V
V CC
R E FE R E NC E C OR E
0.8V R E F OK
PO W E R FA ULT 4.25 V ON 4.05 V OFF 145C O N 135C O FF VC C UV LO
THE R MA L S HUTDOW N
SET DOMINA NT S Q HIC C UP FAULT
0.25V VP OS 5V LINE A R R E GULA TOR V FB INT
S HOR TC IR C UIT DE TE C TION
R
GND 200ms D elay OV E R C UR R E NT DE TE C TION C OU NTE R C LK
V IN 60 mV R E F OK
C LR
140K UV IN 2.50 V ON 2.20 V O FF 50K VIN UV LO
IS P
IS N
T HE R MA L A ND O V E R C UR R E NT P R O T E C T IO N
UV LO C O MP A R AT O R S
Note: Note:TheSP7661usestheSipexPWMcontrollerSP6136 The SP7663 uses the Sipex PWM controller SP6136.
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
4
PIN DESCRIPTION
SP7661
DFN PACKAGE 7mm x 4mm (Option 2) LX 26 LX 25 LX 24 LX 23 VCC 2 2 UVIN 21 GND 20 GND 19 VIN 18 BST 17 LX 16 LX 15 LX 14 Heatsink Pad 3 Connect to VINP Pin 29 Heatsink Pad 2 Connect to GND Pin 28 Pin 27 1 BOTTOM VIEW Heatsink Pad 1 Connect to Lx 2 3 4 5 6 7 8 9 PGND PGND PGND PGND GND VFB COMP SS GND
10 ISN 11 ISP 12 SWN 13 VINP
Pin Pin # Name Description 1-4 PGND Groundconnectionforthesynchronousrectifier. GroundPin.ThecontrolcircuitryoftheICandlowerpowerdriverarereferencedtothis 5,9, GND 19,20 pin.Returnseparatelyfromothergroundtracestothe(-)terminalofCOut. FeedbackVoltageandShortCircuitDetectionpin.Itistheinvertinginputofthe Error Amplifier and serves as the output voltage feedback point for the Buck Converter.Theoutputvoltageissensedandcanbeadjustedthroughanexternal resistordivider.WheneverVFBdrops0.25Vbelowthepositivereference,ashort circuitfaultisdetectedandtheICentershiccupmode.
6
VFB
7
8 0 2 3
14-16, 23-26
OutputoftheErrorAmplifier.Itisinternallyconnectedtotheinvertinginputofthe COMP PWMcomparator.Anoptimalfiltercombinationischosenandconnectedtothis pinandeithergroundorVFBtostabilizethevoltagemodeloop. SoftStart.ConnectanexternalcapacitorbetweenSSandGNDtosetthesoftstart SS ratebasedonthe10Asourcecurrent.TheSSpinisheldlowviaa1mA(min) currentduringallfaultconditions. ISN Currentsensenegativeinput.Rail-to-railinputforovercurrentdetection. ISP SWN VINP LX BST VIN UVIN VCC Currentsensepositiveinput.Rail-to-railinputforovercurrentdetection. LowersupplyrailfortheGHhigh-sidegatedriver.Connectthispintotheswitching nodeascloseaspossibletopins23-27.Donotconnectthispintopins14-16. InputconnectiontothehighsideN-channelMOSFET. ConnectaninductorbetweenthispinandVOut. Highsidedriversupplypin.ConnectBSTtotheexternalboostdiodeandcapacitor as shown in the TypicalApplication Circuit on page 1. The high side driver is connectedbetweenBSTpinandSWNpin. ViNconnectionforinternalLDOandPWMController. UVLOinputforViNvoltage.ConnectaresistordividerbetweenViNandUVIN tosetminimumoperatingvoltage.Useresistorvaluesbelow20ktooverride internalresistordivider. Outputofinternalregulator.MaybeexterinallybiasedifVin<5V.
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator (c) 2007 Sipex Corporation
7 18 2 22
Mar -07 Rev N
5
THEORY OF OPERATION General Overview The SP7661 is a fixed frequency, voltage mode, synchronous PWM regulator optimizedforhighefficiency.Theparthas beenspecificallydesignedforsinglesupply operationfroma5Vto22Vinput. TheheartoftheSP7661isawidebandwidth transconductanceamplifierdesignedtoaccommodateTypeIIandTypeIIIcompensationschemes.Aprecision0.8Vreference, presentonthepositiveterminaloftheerror amplifier, permits the programming of the output voltage down to 0.8V via the VFB pin.Theoutputoftheerroramplifier,COMP, iscomparedtoa1.1Vpeak-to-peakramp, whichisresponsiblefortrailingedgePWM control.ThisvoltagerampandPWMcontrol logicaregovernedbytheinternaloscillator thataccuratelysetsthePWMfrequencyto 600kHz. The SP7661 contains two unique control featuresthatareverypowerfulindistributed applications. First, nonsynchronous driver controlisenabledduringstartup,toprohibit the low side switch from pulling down the output until the high side switch has attemptedtoturnon.Second,a100%duty cycletimeoutensuresthatthelowsideswitch is periodically enhanced during extended periods at 100% duty cycle. This guarantees the synchronized refreshing of the BSTcapacitorduringverylargedutyratios. TheSP7661alsocontainsanumberofvaluableprotectionfeatures.ProgrammableVIN UVLOallowstheusertosettheexactvalue atwhichtheconversionvoltagecansafely begindown-conversion,andaninternalVCC UVLOwhichensuresthatthecontrolleritself has enough voltage to properly operate. Other protection features include thermal shutdownandshort-circuitdetection.Inthe eventthateitherathermal,short-circuit,or UVLOfaultisdetected,theSP7661isforced intoanidlestatewheretheoutputdrivers areheldoffforafiniteperiodbeforearestart isattempted.
Mar -07 Rev N
Soft Start "SoftStart"isachievedwhenapowerconverter ramps up the output voltage while controllingthemagnitudeoftheinputsupplysourcecurrent.Inamodernstepdown converter,rampingupthepositiveterminal oftheerroramplifiercontrolssoftstart.Asa result,excesssourcecurrentcanbedefined asthecurrentrequiredtochargetheoutput capacitor. IViN = COut*(VOut/TSOft-StArt) TheSP7661providestheuserwiththeoptiontoprogramthesoftstartratebytying a capacitor from the SS pin to GND.The selectionofthiscapacitorisbasedonthe 10ApullupcurrentpresentattheSSpin andthe0.8Vreferencevoltage.Therefore, theexcesssourcecanberedefinedas: IViN = COut * [VOut*10A/(CSS*0.8V)]
Under Voltage Lock Out (UVLO) TheSP7661hastwoseparateUVLOcomparatorstomonitorthebias(Vcc)andInput (ViN)voltagesindependently.TheVccUVLO isinternallysetto4.25V.TheViNUVLOis programmable through UViN pin. When UVINpinisgreaterthan2.5VtheSP7661 ispermittedtostartuppendingtheremoval ofallotherfaults.Apairofinternalresistors isconnectedtoUVINasshowninthefigure below. SP7661
VIN
R6 UVIN
140K
R7 GND
2.5V ON 2.2V OFF 50K
+
Internal and external bias of UVIN
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
6
THEORY OF OPERATION ThereforewithoutexternalbiasingtheViN startthresholdis9.5V.Asmallcapacitormay berequiredbetweenUVINandGNDtofilter outnoise.ForapplicationswithViNof5V or 3.3V, connect UVIN directly to ViN. To programtheViN startthreshold,useapair of external resistors as shown. If external resistorsareanorderofmagnitudesmaller than internal resistors, then the ViN start thresholdisgivenby: ViN(start)=2.5*(R6+R7)/R7 Forexample,ifitisrequiredtohaveaViN startthresholdof7V,thenletR7=5Kand usingtheViN startthresholdequationweget R6=9.09K. Thermal and Short-Circuit Protection BecausetheSP7661isdesignedtodrive largeoutputcurrent,thereisachancethat the power converter will become too hot. Therefore, an internal thermal shutdown (145C)hasbeenincludedtopreventthe IC from malfunctioning at extreme temperatures. A short-circuit detection comparator has alsobeenincludedintheSP7661toprotect againstanaccidentalshortattheoutputof thepowerconverter.Thiscomparatorconstantlymonitorsthepositiveandnegative terminalsoftheerroramplifier,andiftheVfB pinfallsmorethan250mV(typical)below the positive reference, a short-circuit fault is set. Because the SS pin overrides the internal0.8Vreferenceduringsoftstart,the SP7661iscapableofdetectingshort-circuit faultsthroughoutthedurationofsoftstartas wellasinregularoperation. Over-Current Protection The Over-current protection feature can onlybeusedonoutputvoltages3.3volts. It is limited by the common mode rating of the op-amp used to sense the voltage
Mar -07 Rev N
across the inductor. Over-current is detected by monitoring a differential voltage acrosstheoutputinductorasshowninthe nextfigure.
SP7661
SWN L=2.7uH,DCR=4.1m
VOUT
R3 5.11K
R4 5.11K
ISP ISN CSP 6.8nF CS 0.1uF
Over-current detection circuit Inputs to an over-current detection comparator,settotriggerat60mVnominal,are connectedtotheinductorasshown.Since the average voltage sensed by the comparatorisequaltotheproductofinductor currentandinductorDCresistance(DCR), thenIMAx=60mV/DCR.Solvingthisequationforthespecificinductorincircuit1,IMAx =14.6A.WhenIMAxisreached,a220ms time-out is initiated, during which top and bottomdriversareturnedoff.Followingthe time-out,arestartisattempted.Ifthefault conditionpersists,thenthetime-outisrepeated(referredtoashiccup). Increasing the Current Limit IfitisdesiredtosetIMAx>{60mV/DCR}(in thiscaselargerthan14.6A),thenaresistor R9 shouldbeaddedasshowninthenext figure.R9formsaresistordividerandreducesthevoltageseenbythecomparator. (IMAx *DCR) Since:60mV = R9 {R3+R4+R9}
(c) 2007 Sipex Corporation
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
7
THEORY OF OPERATION SolvingforR9weget: R9=[60mV*(R3+R4)] [(IMAx *DCR)-60mV] Asanexample:ifdesiredIMAxis17A,then R9=63.4K. R8= R4 * [VOut -60mV+(IMAX* DCR)] 60mV-(IMAX *DCR) Asanexample:forIMAxof4AandVOutof3.3V, calculatedR8is381k.
SP7661
SWN L=2.7uH,DCR=4.1m
SP7661
VOUT
SWN
L=2.7uH,DCR=4.1m
VOUT
R3 5.11K R9 63.4K
R4 5.11K
R3 5.11K
R4 5.11K
ISP ISN CSP 6.8nF
ISP ISN
CS 0.1uF
CSP 6.8nF
CS 0.1uF
R8 1.5M
Over-current detection circuit for Imax > 60mV / DCR Decreasing the Current Limit IfitisrequiredtosetIMAx<{60mV/DCR, a resistorisaddedasshowninthefollowing figure.R8increasesthenetvoltagedetected bythecurrent-sensecomparator.Voltageat thepositiveandnegativeterminalofcomparatorisgivenby: VSP = VOut+(IMAx *DCR) VSN = VOut * {R8/(R4+R8)} Sincethecomparatoristriggeredat60mV: VSP-VSN=60mV CombiningtheaboveequationsandsolvingforR8:
Over-current detection circuit for Imax < {60mV / DCR} Handling of Faults Uponthedetectionofpower(UVLO),thermal, or short-circuit faults, the SP7661 is forcedintoanidlestatewheretheSSand COMPpinsarepulledlowandbothswitches areheldoff.IntheeventofUVLOfault,the SP7661remainsinthisidlestateuntilthe UVLOfaultisremoved.Uponthedetection ofathermalorshort-circuitfault,aninternal 100mstimerisactivated.Intheeventofa short-circuitfault,arestartisattemptedimmediatelyafterthe100mstimeoutexpires. Whereas,whenathermalfaultisdetected the100msdelaycontinuouslyrecyclesanda restartcannotbeattempteduntilthethermal faultisremovedandthetimerexpires.
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
8
APPLICATIONS INFORMATION Error Amplifier and Voltage Loop TheheartoftheSP7661voltageerrorloop is a high performance, wide bandwidth transconductance amplifier. Because of theamplifier'scurrentlimited(+/-150A) transconductance,therearemanywaysto compensatethevoltagelooportocontrolthe COMPpinexternally.Ifasimple,single-pole, single-zeroresponseisdesired,thencompensationcanbeassimpleasanRCcircuit toGround.Ifamorecomplexcompensation isrequired,thentheamplifierhasenough bandwidth(45at4MHz),andenoughgain (60dB)torunTypeIIIcompensationschemes withadequategainandphasemarginsat crossoverfrequenciesgreaterthan50kHz. Thecommonmodeoutputoftheerroramplifieris0.9Vto2.2V.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.
VBST GH Voltage VSWN V(VCC) GL Voltage 0V V(VIN) SWN Voltage -0V -V(Diode) V V(VIN)+V(VCC) BST Voltage V(VCC) TIME
Mar -07 Rev N
The second feature is a 100% duty cycle timeoutthatensuressynchronizedrefreshingoftheBSTcapacitoratveryhighduty 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 applicationbytakingadvantageoftheintegrated-over-temperatureprotectivescheme employedintheSP7661.TheSP7661incorporatesabuilt-inovertemperature protection topreventinternaloverheating. Setting Output Voltages TheSP7661canbesettodifferentoutput voltages.The relationship in the following formulaisbasedonavoltagedividerfrom theoutputtothefeedbackpinVfB,whichis settoaninternalreferencevoltageof0.80V. Standard1%metalfilmresistorsofsurface mountsize0603arerecommended. VOut=0.80V[R1/R2+1] => R2=R1/[ (VOut/0.80V)-1] Where R1=10Kand forVOut=0.80V setting,simplyremoveR2fromtheboard. Furthermore,onecouldselectthevalueof theR1andR2combinationtomeettheexact outputvoltagesettingbyrestrictingtheR1 resistance range such that 10K < R1 < 100Kforoverallsystemloopstability.
(c) 2007 Sipex Corporation
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
9
APPLICATIONS INFORMATION Inductor Selection Therearemanyfactorstoconsiderinselectingtheinductorincludingcorematerial, inductancevs.frequency,currenthandling capability,efficiency,sizeandEMI.InatypicalSP7661circuit,theinductorischosen primarilyforvalue,saturationcurrentandDC resistance.Increasingtheinductorvaluewill decreaseoutputvoltageripple,butdegrade transientresponse.Lowinductorvaluesprovidethesmallestsize,butcauselargeripple currents,poorefficiencyandrequiremore outputcapacitancetosmoothoutthelarger ripple current. The inductor must be able tohandlethepeakcurrentattheswitching frequencywithoutsaturating,andthecopper resistanceinthewindingshouldbekeptas lowaspossibletominimizeresistivepower loss.Agoodcompromisebetweensize,loss andcostistosettheinductorripplecurrent tobewithin20%to40%ofthemaximum outputcurrent. The switching frequency and the inductor operatingpointdeterminetheinductorvalue asfollows: L= where:
.
andprovidelowcorelossatthehigh switchingfrequency.Lowcostpowderedironcoreshaveagradualsaturationcharacteristicbutcanintroduceconsiderable ACcoreloss,especiallywhentheinductorvalueisrelativelylowandtheripple currentishigh.Ferritematerials,although moreexpensive,haveanabruptsaturationcharacteristicwiththeinductance droppingsharplywhenthepeakdesign currentisexceeded.Nevertheless,they arepreferredathighswitchingfrequenciesbecausetheypresentverylowcore losswhilethedesignerisonlyrequired to preventsaturation.Ingeneral,ferrite ormolypermalloymaterialsareabetter choiceforallbutthemostcostsensitive applications. Optimizing Efficiency Thepowerdissipatedintheinductorisequal tothesumofthecoreandcopperlosses. To minimize copper losses, the winding resistanceneedstobeminimized,butthis usually comes at the expense of a larger inductor.Corelosseshaveamoresignificant contributionatlowoutputcurrentwherethe copperlossesareataminimum,andcan typicallybeneglectedathigheroutputcurrents where the copper losses dominate. Core loss information is usually available from the magnetics vendor. Proper inductorselectioncanaffecttheresultingpower supplyefficiencybymorethan15%! Thecopperlossintheinductorcanbecalculatedusingthefollowingequation: PL(Cu) = I L(rMS) * rwiNDiNg whereIL(rMS)istheRMSinductorcurrent thatcanbecalculatedasfollows: IL(rMS) = IOut(MAx) *
2
ViN(MAx) * s*Kr * IOut(MAx)
VOut*(ViN(MAx) - VOut)
s=switchingfrequency
Kr=ratiooftheACinductorripplecurrent tothemaximumoutputcurrent Thepeak-to-peakinductorripplecurrentis: IPP =
.V
Out*(ViN(MAx)
ViN(MAx) * s*L
- VOut)
Oncetherequiredinductorvalueisselected, theproperselectionofcorematerialisbased onpeakinductorcurrentandefficiencyrequirements.Thecoremustbelargeenough nottosaturateatthepeakinductorcurrent
Mar -07 Rev N
IPeAk = IOut(MAx) +
IPP 2
( )
+ 3
.
IPP IOut(MAx)
2
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
0
APPLICATIONS INFORMATION Output Capacitor Selection TherequiredESR(EquivalentSeriesResistance)andcapacitancedrivetheselectionofthetypeandquantityoftheoutput capacitors.TheESRmustbesmallenough thatboththeresistivevoltagedeviationdue to a step change in the load current and the output ripple voltage do not exceed thetolerancelimitsexpectedontheoutput voltage. During an output load transient, theoutputcapacitormustsupplyalltheadditionalcurrentdemandedbytheloaduntil theSP7661adjuststheinductorcurrentto thenewvalue. In order to maintain VOut,the capacitance must be large enough so that the output voltage is held up while the inductor current ramps to the value corresponding to the new load current. Additionally, the ESRintheoutputcapacitorcausesastep intheoutputvoltageequaltothecurrent. Becauseofthefasttransientresponseand inherent100%to0%dutycyclecapability providedbytheSP7661whenexposedto outputloadtransients,theoutputcapacitor istypicallychosenforESR,notforcapacitancevalue. TheESRoftheoutputcapacitor,combined withtheinductorripplecurrent,istypically themaincontributortooutputvoltageripple. ThemaximumallowableESRrequiredto maintainaspecifiedoutputvoltageripplecan becalculatedby: ReSr VOut IPk-Pk VOut =
s=SwitchingFrequency
D=DutyCycle COut = Output Capacitance Value
Input Capacitor Selection
(
IPP *(1-D)
s*COut
)
2
+(IPP *ReSr)
2
Theinputcapacitorshouldbeselectedfor ripple current rating, capacitance and voltagerating.Theinputcapacitormustmeet theripplecurrentrequirementimposed bytheswitchingcurrent.Incontinuous conductionmode,thesourcecurrentof thehigh-sideMOSFETisapproximatelya squarewaveofdutycycleVOut/ViN.More accurately,thecurrentwaveformistrapezoidal,givenafiniteturn-onandturn-off, switchtransitionslope.Mostofthiscurrent issuppliedbytheinputbypasscapacitors.TheRMScurrenthandlingcapability oftheinputcapacitorsisdeterminedat maximumoutputcurrentandunderthe assumptionthatthepeak-to-peakinductor ripplecurrentislow,itisgivenby:
ICiN(rMS) = IOut(MAx) * D(1 - D)
Theworstcaseoccurswhenthedutycycle Dis50%andgivesanRMScurrentvalue equaltoIOUT/2.Selectinputcapacitorswith adequateripplecurrentratingtoensurereliableoperation. The power dissipated in the input capacitoris: PCiN = I CiN(rMS) * reSr(CiN) Thiscanbecomeasignificantpartofpower losses in a converter and hurt the overall energy transfer efficiency. The input voltage ripple primarily depends on the input
2
where:
VOut = Peak-to-Peak Output Voltage Ripple IPk-Pk = Peak-to-Peak Inductor Ripple Current Thetotaloutputrippleisacombinationof theESRandtheoutputcapacitancevalue andcanbecalculatedasfollows:
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
APPLICATIONS INFORMATION capacitor ESR and capacitance. Ignoring theinductorripplecurrent,theinputvoltage ripplecanbedeterminedby: ViN = Loop Compensation Design Theopenloopgainofthewholesystemcan bedividedintothegainoftheerroramplifier,PWMmodulator,buckconverteroutput stage,andfeedbackresistordivider.Inorder tocrossoveratthedesiredfrequencycut-off (FCO),thegainoftheerroramplifiermust compensatefortheattenuationcausedby therestoftheloopatthisfrequency.The goal of loop compensation is to manipulateloopfrequencyresponsesuchthatits crossovergainat0db,resultsinaslopeof -20db/decade. The first step of compensation design is topicktheloopcrossoverfrequency.High crossover frequency is desirable for fast transientresponse,butoftenjeopardizesthe powersupplystability.Crossoverfrequency should be higher than the ESR zero but lessthan1/5oftheswitchingfrequencyor
IOut(MAx)*reSr(CiN) + IOut(MAx)*VOut*(ViN - VOut) V2iN * s*CiN
The capacitor type suitable for the output capacitors can also be used for the input capacitors.However,exerciseextracaution whentantalumcapacitorsareused.Tantalum capacitorsareknownforcatastrophicfailure whenexposedtosurgecurrent,andinput capacitorsarepronetosuchsurgecurrent whenpowersuppliesareconnected"live" tolowimpedancepowersources.Although tantalumcapacitorshavebeensuccessfully employed at the input, it is generally not recommended.
Type III Voltage Loop Compensation GAMP (s) Gain Block VREF (Volts) (SRz2Cz2+1)(SR1Cz3+1) SR1Cz2(SRz3Cz3+1)(SRz2Cp1+1) Notes: RESR = Output Capacitor Equivalent Series Resistance. RDC = Output Inductor DC Resistance. VRAMP_PP = SP7662 Internal Ramp Amplitude Peak-to-Peak Voltage. Condition: Cz2 >> Cp1 & R1 >> Rz3 Output Load Resistance >> RESR & RDC
PWM Stage GPWM Gain Block VIN VRAMP_PP
Output Stage GOUT (s) Gain Block (SRESRCOUT+ 1) [S^2LCOUT+S(RESR+RDC) COUT+1]
VOUT (Volts)
Voltage Feedback GFBK Gain Block R2 VFBK (Volts) (R1 + R2) or VREF VOUT
SP7661 Voltage Mode Control Loop with Loop Dynamic
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
2
120kHz.TheESRzeroiscontributedbythe ESRassociatedwiththeoutputcapacitors andcanbedeterminedby:
APPLICATIONS INFORMATION P(LC) = 2* L* COut
.
z(ESR) =
2* COut * ReSr
The next step is to calculate the complex conjugate poles contributed by the LC outputfilter,
Gain (dB)
WhentheoutputcapacitorsareofaCeramic Type,theSP7661EvaluationBoardrequires aTypeIIIcompensationcircuittogiveaphase boostof180inordertocounteracttheeffects ofanunderdampedresonanceoftheoutput filteratthedoublepolefrequency.
Condition: C22 >> CP1, R1 >> RZ3
Error Amplifier Gain Bandwidth Product
20 Log (RZ2/R1)
1/6.28 (RZ2) (CP1)
1/6.28 (RZ3) (CZ3)
1/6.28 (R1) (CZ3)
1/6.28(R22) (CZ2)
1/6.28 (R1) (CZ2)
Frequency (Hz)
Bode Plot of Type III Error Amplifier Compensation.
CP1
RZ3
CZ3
CZ2 VFB RSET
RZ2
VOUT
R1 68.1k, 1%
+ + - 0.8V
COMP CF1
RSET =
54.48 (k) (VOUT -0.8)
Type III Error Amplifier Compensation Circuit
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
3
APPLICATIONS INFORMATION
LX
L1, Wurth -744311220 2.2uH, 14 mOhm, 7x7mm, 9A R3 5.11K C4 47nF 61.9k
ISP ISN
VOUT 3.30V, 0-3A
1
3
R4 5.11K
28
27
R11 0 Ohm C5 100uF RZ3 400 R1 10k
SWN PAD
GND PAD
1 2
PGND PGND PGND PGND GND VFB COMP SS GND ISN ISP SWN
LX LX
26
C6 NP
C7 NP
R9
25 24 23 22 21 20 19 18 17 16 15 14
RBST
CZ2 6800pF CP1
RZ2 4.02k 56pF
3 4 5 6 7
U1 SP7661
LX LX VCC UVIN GND GND VIN BST LX LX
1
4
CVCC 4.7uF
R12 NP
GND
CZ3 1500pF R7 NP C8 NP
CF1 100pF
CSS
47nF
8 9
R14 NP
R2 3160
R6 NP
R8
NP
10 11
0 Ohm 22nF CBST
C9
6.8nF
12 13
SD101AWS DBST
VIN
VIN PAD
LX
ISN ISP LX
29
LX
Rs1 NP
Cs1 NP
Rs2
Cs2
VIN
1
12V (9.6V-22V)
1
1 Ohm
2.2nF
C3 NP
C2 22uF
C1 22uF
1
2
GND
Evaluation Board Schematic Parts shown for 9.6V-22V input, 3.3V Output
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
14
TYPICAL PERFORMANCE CHARACTERISTICS
00 90
Efficiency vs. Load at 22VIN
00 90 80 70 60 50 40
Efficiency vs Load at 12VIN
Efficiency (%)
70 60 50 40 0.5 1.0 1.5 2.0 2.5 3.0 Vout=5.0V Vout=3.3V Vout=2.5V Vout=1.8V
Efficiency (%)
80
Vout=5.0V Vout=3.3V Vout=2.5V Vout=1.8V Vout=1.5V Vout=1.2V 0.5 1.0 1.5 2.0 2.5 3.0
Output Load (A)
Output Load (A)
00 95
Efficie ncy v s. Load at 5.0VIN
00 95
Efficiency vs. Load at 3.3VIN
85 80 75 70 0.5 1.0 1.5 2.0 2.5 3.0 Vout=3.3V Vout=2.5V Vout=1.8V Vout=1.5V Vout=1.2V Vout=0.8V
Efficiency (%)
Efficiency (%)
90
90 85 80 75 70 2 2 3 3 Vout=2.5V Vout=1.8V Vout=1.5V Vout=1.2V Vout=0.8V
Output Load (A)
Output Load (A)
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
15
TYPICAL PERFORMANCE CHARACTERISTICS
TransientResponse: CH1:VOut. CH4:IOut1A/div.
TransientResponse:CH1:VOut.CH4: IOut1A/div.zoomshowing~1.5A/usIrate
TransientResponse: CH1:VOut. CH4:IOut1A/div.
ShortCircuitProtection:CH1:VOut. CH2:Sstart.CH4:IOut(10A/div).
ShortCircuitProtection:CH1:VOut.CH2: Sstart.CH4:InputCurrent(5A/div).
ShortCircuitProtection:CH1:VOut. CH2:Sstart.CH4:InputCurrent(5A/div). 104msrestartrateshown .
(c) 2007 Sipex Corporation
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
6
TYPICAL PERFORMANCE CHARACTERISTICS
Start-upinto3ALoad:CH1:VOut. CH2:SS.CH3:ViN. CH4:Iout(2A/div).
CurrentLimit:CH1:VOut. CH2:SoftStart. CH4IOut(2A/div).Currentisreaching approximtely6Abeforea shutdown&restart
CurrentLimit:CH1:VOut. CH2:SoftStart. CH4IOut(2A/div). OCPRepeatrateis107ms
12VinOutputRipple:CH1:VOut.CH2: SwitchNodetakenat3AOut.
12VinOutputRipple:CH1:VOut. CH2:SwitchNodetakenat0AOut.
Mar -07 Rev N
22VinOutputRipple:CH1:VOut. CH2:SwitchNodetakenat0Aout.
(c) 2007 Sipex Corporation
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
7
TYPICAL PERFORMANCE CHARACTERISTICS
22VinTransientResponse CH1:VOut. CH4:IOut(1A/div).
Operationfromexernalbias: CH2:Switchnode@2.34ViN.
Operationfromexernalbias: CH2:Switchnode@3ViN, IOut=3A.
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
18
PACKAGE: 26 PIN DFN
Mar -07 Rev N
SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator
(c) 2007 Sipex Corporation
19
ORDERING INFORMATION
Part Number
Junction Temperature
Package
SP7661ER/TR..................................-40Cto+125C...................................................26Pin7X4DFN (Option2) SP7661ER-L/TR...............................-40Cto+125C......................... LeadFree)26Pin7X4DFN ( (Option2)
/TR=TapeandReel Packquantityis3,00026pinDFN.
Sipex Corporation Headquarters and Sales Office 233SouthHillviewDrive Milpitas,CA95035 TEL:(408)934-7500 FAX:(408)935-7600 SipexCorporationreservestherighttomakechangestoanyproductsdescribedherein.Sipexdoesnotassumeanyliabilityarisingoutofthe applicationoruseofanyproductorcircuitdescribedherein;neitherdoesitconveyanylicenseunderitspatentrightsnortherightsofothers. Mar -07 Rev N SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator (c) 2007 Sipex Corporation
20

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