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LTC3541-2 High Efficiency Buck + VLDO Regulator
High Efficiency, 500mA Buck Plus 300mA VLDO Regulator Auto Start-Up Powers Buck Output Prior to VLDO/ Linear Regulator Output Independent 500mA High Efficiency Buck (VIN: 2.7V to 5.5V) 300mA VLDO Regulator with 30mA Standalone Mode No External Schottky Diodes Required FixedBuck Output Voltage: 1.875V VLDO Input Voltage Range (LV : 1.6V to 5.5V) IN FixedVLDO Output Voltage: 1.5V SelectableFixedFrequency,Pulse-SkipOperation orBurstMode(R)Operation Short-CircuitProtected CurrentModeOperationforExcellentLineandLoad TransientResponse ShutdownCurrent:<3A ConstantFrequencyOperation:2.25MHz LowDropoutBuckOperation:100%DutyCycle Small,ThermallyEnhanced,10-Lead(3mmx3mm) DFNPackage
TheLTC (R)3541-2combinesasynchronousbuckDC/ DCconverterwithaverylowdropoutlinearregulator TM (VLDO regulator)andinternalfeedbackresistornetworks toprovidetwooutputvoltagesfromasingleinputvoltagewithminimalexternalcomponents.Whenconfigured fordualoutputoperation,theLTC3541-2'sautostart-up featurewillbringthe1.875Vbuckoutputintoregulation inacontrolledmanner,priortoenablingthe1.5VVLDO outputwithouttheneedforexternalpincontrol.The 1.5VVLDO/linearregulatoroutputpriorto1.875Vbuck outputsequencingmayalsobeobtainedviaexternalpin control.TheinputvoltagerangeisideallysuitedforLi-Ion batteryapplicationspoweringsub-3.3Vlogicfrom5Vor 3.3Vrails. Thesynchronousbuckconverterprovidesahighefficiency output,typically90%.Itcanprovideupto500mAofoutput currentwhileswitchingat2.25MHz,allowingtheuseof smallsurfacemountinductorsandcapacitors.AmodeselectpinallowsBurstModeoperationtobeenabledfor higherefficiencyatlightloadcurrents,ordisabledforlower noise,constantfrequencyoperation. The VLDO regulator provides a low noise, low voltage outputcapableofprovidingupto300mAofoutputcurrent usingonlya2.2Fceramiccapacitor.Theinputsupply voltageoftheVLDOregulator(LVIN)maycomefromthe buckregulatoroutputoraseparatesupply.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. VLDO is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
APPLICATIO S

DigitalCameras CellularPhones PCCards WirelessandDSLModems OtherPortablePowerSystems
VIN 2.9V TO 5.5V
EFFICIENCY (%)
SW 2.2H
ENVLDO
VIN MODE LTC3541-2 ENBUCK GND VOUT LVIN 10F LVOUT PGND VOUT2 1.5V 300mA
VOUT1 1.875V 200mA
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TYPICAL APPLICATIO
Buck (Burst) Efficiency vs Load Current
100 90 80 70 60 50 40 30 20 10 0 1 10 100 LOAD CURRENT (mA) 0.0001 1000
35412 TA01b
VIN = 3V EFFICIENCY
2.2F
35412 TA01a
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1 0.1 POWER LOSS (W) POWER LOSS 0.01 0.001
FEATURES
DESCRIPTIO
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LTC3541-2
(Note 1)
SupplyVoltages: VIN,LVIN.................................................. -0.3Vto6V LVIN-VIN..........................................................<0.3V PinVoltages: ENVLDO,ENBUCK,MODE,SW......-0.3VtoVIN+0.3V LinearRegulatorIOUT(MAX)(100ms)(Note9)......100mA OperatingAmbientTemperatureRange (Note2)................................................... -40Cto85C . JunctionTemperature(Notes5,10)...................... 125C StorageTemperatureRange.................. -65Cto125C .
TOP VIEW VIN ENBUcK VOUT Nc LVOUT 1 2 3 4 5 11 10 SW 9 ENVLDO 8 MODE 7 GND 6 LVIN
TJMAX=125C,JA=43C/W EXPOSEDPAD(PIN11)ISPGND,MUSTBESOLDEREDTOPCB
DD PAcKAGE 10-LEAD (3mm x 3mm) PLASTIc DFN
ORDERPARTNUMBER LTC3541EDD-2
DDPARTMARKING LCHQ
Order OptionsTapeandReel:Add#TR LeadFree:Add#PBFLeadFreeTapeandReel:Add#TRPBF LeadFreePartMarking:http://www.linear.com/leadfree/ ConsultLTCMarketingforpartsspecifiedwithwideroperatingtemperatureranges.
ELECTRICAL CHARACTERISTICS
SYMBOL IPK VIN VIN(LINEREG) PARAMETER PeakInductorCurrent InputVoltageRange BuckVINLineRegulation (Note4)
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V unless otherwise specified (Note 2)
CONDITIONS VIN=4.2V(Note8)

MIN 0.8 2.7
TYP 0.95 0.04 2.2 2.2 0.8 20 0.5 0.25 0.25
MAX 1.25 5.5 0.4
UNITS A V %/V mV/V mV/V mV/V
VIN=2.7Vto5.5V,ENBUCK=VIN, ENVLDO=0V,MODE=VIN(Note6) VLDOVINLineRegulation VIN=2.9Vto5.5V,LVOUT=1.5V,ENBUCK=VIN, (ReferredtoLVOUT) ENVLDO=VIN,MODE=0V,IOUT(VLDO)=100mA LinearRegulatorVINLine VIN=2.9Vto5.5V,LVOUT=1.5V,ENBUCK=0V, Regulation(ReferredtoLVOUT) ENVLDO=VIN,IOUT(LDO)=10mA LVIN(LINEREG) LVINLineRegulation LVIN=1.6Vto5.5V,VIN=5.5V,LVOUT=1.5V, (ReferredtoLVOUT) ENBUCK=VIN,ENVLDO=VIN,MODE=VIN, IOUT(VLDO)=100mA VLDODO LVIN-LVOUTDropoutVoltage LVOUT=1.5V,ENBUCK=VIN,ENVLDO=VIN, MODE=VIN,IOUT(VLDO)=50mA(Note9) VLOADREG BuckOutputLoadRegulation ENBUCK=VIN,ENVLDO=0V,MODE=VIN(Note6)
50
VVOUT
VLDOOutputLoadRegulation IOUT(VLDO)=1mA-300mA,LVIN=1.875V,LVOUT=1.5V, ENBUCK=VIN,ENVLDO=VIN,MODE=VIN LinearRegulatorOutputLoad IOUT(LDO)=1mA-30mA,LVOUT=1.5V, ENBUCK=0V,ENVLDO=VIN Regulation ReferenceRegulationVoltage ENBUCK=VIN,ENVLDO=0V,TA=25C (Note6) ENBUCK=VIN,ENVLDO=0V,0CTA85C ENBUCK=VIN,ENVLDO=0V,-40CTA85C
0.5 0.5 1.913 1.917 1.922 1.53 1.534 1.538
1.837 1.833 1.828 1.47 1.466
1.875 1.875 1.875 1.5 1.5 1.5
VLVOUT
ReferenceRegulationVoltage (Note7)
ENBUCK=0V,ENVLDO=VIN,TA=25C ENBUCK=0V,ENVLDO=VIN,0CTA85C ENBUCK=0V,ENVLDO=VIN,-40CTA85C
1.462
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mV % % % V V V V V V
W
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WW
W
ABSOLUTE
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
LTC3541-2 ELECTRICAL CHARACTERISTICS
SYMBOL IS PARAMETER Buck+VLDO BurstModeSleep VINQuiescentCurrent Buck+VLDO BurstModeActive VINQuiescentCurrent Buck+VLDO Pulse-SkipModeActive VINQuiescentCurrent Buck BurstModeSleep VINQuiescentCurrent Buck BurstModeActive VINQuiscentCurrent Buck Pulse-SkipModeActive VINQuiescentCurrent LinearRegulatorVINQuiescent Current VINShutdownQuiescent Current LVINShutdownQuiescent Current OscillatorFrequency RDS(ON)ofP-ChannelMOSFET RDS(ON)ofN-ChannelMOSFET SWLeakage InputPinHighThreshold InputPinLowThreshold InputPinCurrent
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V unless otherwise specified (Note 2)
CONDITIONS LVIN=1.875V,LVOUT=1.5V,ENBUCK=VIN, ENVLDO=VIN,MODE=0V,IOUT(VLDO)=10A, VVOUT=2.11V LVIN=1.875V,LVOUT=1.5V,ENBUCK=VIN, ENVLDO=VIN,MODE=0V,IOUT(VLDO)=10A, VVOUT=1.64V LVIN=1.875V,LVOUT=1.5V,ENBUCK=VIN, ENVLDO=VIN,MODE=VIN,IOUT(VLDO)=10A, VVOUT=1.64V VVOUT=2.11V,IOUT(BUCK)=0A,ENBUCK=VIN, ENVLDO=0V,MODE=0V VVOUT=1.64V,IOUT(BUCK)=0A,ENBUCK=VIN, ENVLDO=0V,MODE=0V VVOUT=1.64V,IOUT(BUCK)=0A,ENBUCK=VIN, ENVLDO=0V,MODE=VIN LVOUT=1.5V,ENBUCK=0V,ENVLDO=VIN, IOUT(VLDO)=10A ENBUCK=0V,ENVLDO=0V LVIN=3.6V,ENBUCK=0V,ENVLDO=0V
MIN
TYP 85 315 300 55 300 285 50 2.5 0.1
MAX
UNITS A A A A A A A A A
fOSC RPFET RNFET ILSW VIH VIL IMODE, IENBUCK, IENVLDO
1.8
2.25 0.25 0.35 0.01
2.7
MHz
ISW=100mA ISW=-100mA Enable=0V,VSW=0Vor6V,VIN=6V MODE,ENBUCK,ENVLDO MODE,ENBUCK,ENVLDO

1 0.3
A V V A
0.9 0.01 1
Note 1:StressesbeyondthoselistedunderAbsoluteMaximumRatings maycausepermanentdamagetothedevice.ExposuretoanyAbsolute MaximumRatingconditionforextendedperiodsmayaffectdevice reliabilityandlifetime. Note 2:TheLTC3541-2isguaranteedtomeetperformancespecifications from0Cto85C.VLDO/linearregulatoroutputistestedandspecified underpulseloadconditionssuchthatTJTA,andare100%production testedat25C.Specificationsoverthe-40Cto85Coperating temperaturerangeareassuredbydesign,characterizationandcorrelation withstatisticalprocesscontrols. Note 3:MinimumoperatingLVINvoltagerequiredforVLDOregulationis: LVINLVOUT+VDROPOUT. Note 4:MinimumoperatingVINvoltagerequiredforVLDOandlinear regulatorregulationis: VINLVOUT+1.4V. Note 5:TJiscalculatedfromtheambienttemperature,TA,andpower dissipation,PD,accordingtothefollowingformula: TJ=TA+(PD*43C/W)
Note 6:TheLTC3541-2istestedinaproprietarytestmodethatconnects VBUCKFBtotheoutputoftheerroramplifier.Forthereferenceregulation andlineregulationtests,theoutputoftheerroramplifierissettothe midpoint.Fortheloadregulationtest,theoutputoftheerroramplifieris driventotheminimumandmaximumofthesignalrange. Note 7:Measurementmadeinclosedlooplinearregulatorconfiguration withLVOUT=1.5V,ILOAD=10A. Note 8:Measurementmadeinaproprietarytestmodewithslope compensationdisabled. Note 9:Measurementisassuredbydesign,characterizationandstatistical processcontrol. Note 10:ThisICincludesovertemperatureprotectionthatisintended toprotectthedeviceduringmomentaryoverloadconditions.Junction temperaturewillexceed125Cwhenovertemperatureprotectionisactive. Continuousoperationabovethespecifiedmaximumoperatingjunction temperaturemayimpairdevicereliability.
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LTC3541-2 TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage for Buck (Pulse Skip)
95 90 85 EFFICIENCY (%) IOUT = 100mA EFFICIENCY (%) 80 75 70 65 60 55 50 2 3 4 INPUT VOLTAGE (V)
35412 G01
IOUT = 500mA
EFFICIENCY (%)
IOUT = 30mA
5
Efficiency vs Load Current for Buck (Burst)
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1 10 100 LOAD CURRENT (mA) 1000
35412 G04
VIN = 3.6V
VIN = 2.7V VIN = 4.2V
DROPOUT VOLTAGE (mV)
BIAS CURRENT (A)
Output (Auto Start-Up Sequence, Buck in Pulse Skip) vs Time
2.50 2.45 VOUT 1V/DIV LVOUT 1V/DIV VIN 2V/DIV FREQUENCY (MHz) 2.40 2.35 2.30 2.25 2.20 2.15 2.10 2.05
IVOUT = 200mA ILVOUT = 300mA
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6
Efficiency vs Input Voltage for Buck (Burst)
100 95 90 85 80 75 70 65 60 55 50 2 3 4 5 INPUT VOLTAGE (V) 6
35412 G02
Efficiency vs Load Current for Buck (Pulse Skip)
100 90 VIN = 2.7V VIN = 3.6V VIN = 4.2V
IOUT = 500mA
80 70 60 50 40 30 20 10 0 0.1 1
IOUT = 100mA
IOUT = 30mA
10 100 LOAD CURRENT (mA)
1000
35412 G03
VLDO Dropout Voltage vs Load Current
100 250 VIN = 3V VIN = 3.6V 60 VIN = 4.2V 40 200
Buck (Burst) Plus VLDO Bias Current vs VLDO Load Current
VIN = 3.6V ILOAD_BUCK = 0 IBIAS = IVIN + ILVIN - ILOAD
80
150 100
20 0
50
0
50
100 150 200 LOAD CURRENT (mA)
250
300
0 0.1
1
10 100 LOAD CURRENT (mA)
1000
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Oscillator Frequency vs Temperature
VIN = 3.6V
2ms/DIV
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2.00 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
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LTC3541-2 TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency vs Supply Voltage
2.5 VIN = 3.6V 0.410 0.408 0.406 REFERENCE (V) 0.404 0.402 0.400 0.398 0.396 0.394 0.392 2.0 3 5 4 SUPPLY VOLTAGE (V) 6
35412 G09
2.4 FREQUENCY (MHz)
REFERENCE (V)
2.3
2.2
2.1
RDS(0N) vs Temperature
0.700 0.600 0.500 RDS(ON) () 0.400 0.300 0.200 0.100 MAIN SWITCH VIN = 2.5V VIN = 3.6V VIN = 5.5V 100 125 LVOUT 10mV/DIV AC COUPLED VOUT 10mV/DIV AC COUPLED
SYNCH SWITCH
0 -50 -25
50 25 75 0 TEMPERATURE (C)
Buck (Burst) Load Step from 1mA to 500mA
VOUT 100mV/DIV AC COUPLED IL 500mA/DIV ILOAD 500mA/DIV VIN = 3.6V 40s/DIV VOUT = 1.875V ILOAD = 1mA TO 500mA
35412 G12
UW
35412 G10
VLDO/Linear Regulator Reference vs Temperature
VIN = 3.6V 0.820 0.816 0.812 0.808 0.804 0.800 0.796 0.792 0.788 0.784 50 25 0 75 TEMPERATURE (C) 100 125
Buck Reference vs Temperature
VIN = 3.6V
0.390 -50 -25
0.780 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
35412 G19
35412 G20
Buck (Burst) and VLDO Output
VOUT 100mV/DIV AC COUPLED IL 500mA/DIV ILOAD 500mA/DIV VIN = 3.6V 2s/DIV LVOUT = 1.5V VOUT = 1.875V ILOAD = 50mA Burst Mode OPERATION
35412 G21
Buck (Pulse Skip) Load Step from 1mA to 500mA
VIN = 3.6V 40s/DIV VOUT = 1.875V ILOAD = 1mA TO 500mA
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VLDO Load Step from 1mA to 300mA
VLDO Load Step from 100mA to 300mA
LVOUT 20mV/DIV AC COUPLED
LVOUT 20mV/DIV AC COUPLED
ILOAD 250mA/DIV VIN = 3.6V 200s/DIV VOUT = 1.5V ILOAD = 1mA TO 300mA
35412 G13
ILOAD 250mA/DIV
VIN = 3.6V 200s/DIV LVOUT = 1.5V ILOAD = 100mA TO 300mA
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LTC3541-2 TYPICAL PERFOR A CE CHARACTERISTICS
Linear Regulator to VLDO Transient Step, Load = 1mA
LVOUT 10mV/DIV AC COUPLED
ILOAD 50mA/DIV
VIN = 3.6V LVOUT = 1.5V ILOAD = 1mA
VLDO to Linear Regulator Transient Step, Load = 1mA
LVOUT 10mV/DIV AC COUPLED
ILOAD 50mA/DIV
VIN = 3.6V LVOUT = 1.5V ILOAD = 1mA
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Linear Regulator to VLDO Transient Step, Load = 30mA
LVOUT 10mV/DIV AC COUPLED ILOAD 50mA/DIV
40s/DIV
35412 G15
VIN = 3.6V LVOUT = 1.5V ILOAD = 30mA
40s/DIV
35412 G16
VLDO to Linear Regulator Transient Step, Load = 30mA
LVOUT 10mV/DIV AC COUPLED ILOAD 50mA/DIV
40s/DIV
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VIN = 3.6V LVOUT = 1.5V ILOAD = 30mA
40s/DIV
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LTC3541-2 PI FU CTIO S
VIN (Pin 1):MainSupplyPin.Thispinmustbeclosely decoupledtoGNDwitha10Forgreatercapacitor. ENBUCK (Pin 2):BuckEnablePin.Thispinenablesthe buckregulatorwhendriventoalogichigh. VOUT (Pin 3):BuckRegulatorOutputPin.Thispinreceives thebuckregulator'soutputvoltage. NC (Pin 4):NotConnected.Thispinmustnotbeconnected orcapacitivelyloaded. LVOUT (Pin 5):VLDO/LinearRegulatorOutputPin.This pinprovidestheregulatedoutputvoltagefromtheVLDO orlinearregulator. LVIN (Pin 6): VLDO/Linear Regulator Input Supply Pin. ThispinprovidestheinputsupplyvoltagefortheVLDO powerFET. GND (Pin 7):AnalogGroundPin. MODE (Pin 8):BuckModeSelectionPin.Thispinenables buck Pulse-Skip operation when driven to a logic high andenablesbuckBurstModeoperationwhendrivento alogiclow. ENVLDO (Pin 9): VLDO/Linear Regulator Enable Pin. Whendriventoalogichigh,thispinenablesthelinear regulatorwhentheENBUCKpinisdriventoalogiclow, andenablestheVLDOregulatorwhentheENBUCKpinis driventoalogichigh.
1 0 1
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SW (Pin 10): Switch Node Pin. This pin connects the internalmainandsynchronouspowerMOSFETswitches totheexternalinductorforthebuckregulator. Exposed Pad (Pin 11): Ground Pin. This pin must be solderedtothePCBtoprovidebothelectricalcontactto groundandgoodthermalcontacttothePCB. Note:Table1detailsthetruthtableforthecontrolpins oftheLTC3541-2.
Table 1. LTC3541-2 Control Pin Truth Table
PIN NAME ENBUCK 0 0 1 ENVLDO 0 1 0 MODE X X 0 LTC3541-2PoweredDown BuckPoweredDown,VLDOPowered Down,LinearRegulatorEnabled BuckEnabled,VLDOPoweredDown, LinearRegulatorPoweredDown, BurstModeOperation BuckEnabled,VLDOPoweredDown, LinearRegulatorPoweredDown, Pulse-SkipModeOperation BuckEnabled,VLDOEnabled,Linear RegulatorPoweredDown,BurstMode Operation BuckEnabled,VLDOEnabled,Linear RegulatorPoweredDown,Pulse-Skip ModeOperation OPERATIONAL DESCRIPTION
1
1
0
1
1
1
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LTC3541-2 W
2.2H 10 1 VIN SW VOUT(BUCK) = 1.875V IOUT(BUCK) = 500mA 10F VOUT PGND LVIN 3 6 VLDO/LINEAR REG REF VIN LVIN LVOUT = 1.5V IOUT = 300mA (LDO) IOUT = 30mA (LINEAR REG) LVOUT GND 5 2.2F
FU CTIO AL BLOCK DIAGRA
VIN(MIN) LVOUT + 1.4V
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500mA BUCK VIN SW REF FB GND
REF ENBUCK ENVLDO MODE CONTROL LOGIC
+ -
LFB CNTRL
2 9 8
GND 7
PGND 11
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Figure 1. LTC3541-2 Functional Block Diagram
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LTC3541-2
TheLTC3541-2containsahighefficiencysynchronous buckconverter,averylowdropoutregulator(VLDO),and alinearregulatorthatcanbeusedtoprovideuptotwo outputvoltagesfromasingleinputvoltagemakingthe LTC3541-2idealforapplicationswithlimitedboardspace. Thecombinationandconfigurationofthesemajorblocks withintheLTC3541-2isdeterminedbywayofthecontrol pinsENBUCKandENVLDOasdefinedinTable1. WiththeENBUCKpindriventoalogichighandENVLDO driven to a logic low, the LTC3541-2 enables the buck converter to efficiently reduce the voltage provided at theVINinputpintoanoutputvoltageof1.875Vwhich issetbyaninternalfeedbackresistornetwork.Thebuck regulatorcanbeconfiguredforPulse-SkiporBurstMode operationbydrivingtheMODEpintoalogichighorlogic lowrespectively.Thebuckregulatoriscapableofprovidingamaximumoutputcurrentof500mA,whichmustbe takenintoconsiderationwhenusingthebuckregulator toprovidethepowerforboththeVLDOregulatorandfor externalloads. WiththeENBUCKpindriventoalogiclowandENVLDO driventoalogichigh,theLTC3541-2enablesthelinear regulator,providingalownoiseregulatedoutputvoltage of1.5VattheLVOUTpinwhiledrawingminimalquiescent currentfromtheVINinputpin.Thisfeatureallowsoutput voltageLVOUTtobebroughtintoregulationwithoutthe presenceoftheLVINvoltage. With the ENBUCK and ENVLDO pins both driven to a logic high, the LTC3541-2 enables the high efficiency buckconverterandVLDO,providingdualoutputoperationfromasingleinputvoltage.Whenconfiguredinthis manner,theLTC3541-2'sautostart-upsequencingfeature willbringthebuckoutput(1.875V)intoregulationina controlledmannerpriortoenablingtheVLDOregulator (1.5V)withouttheneedforexternalpincontrol.Adetailed discussionofthetransitionsbetweentheVLDOregulatorandlinearregulatorcanbefoundintheVLDO/Linear RegulatorLoopsection.
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Buck Regulator Control Loop TheLTC3541-2internalbuckregulatorusesaconstant frequency,currentmode,step-downarchitecture.Boththe main(top,P-channelMOSFET)andsynchronous(bottom, N-channelMOSFET)switchesareinternal.Duringnormal operation,theinternalmainswitchisturnedonatthebeginningofeachclockcycleprovidedtheinternalfeedback voltagetothebuckislessthanthereferencevoltage.The currentintotheinductorprovidedtotheloadincreases untilthecurrentlimitisreached.Oncethecurrentlimitis reachedthemainswitchturnsoffandtheenergystored in the inductor flows through the bottom synchronous switchintotheloaduntilthenextclockcycle. Thepeakinductorcurrentisdeterminedbycomparingthe buckfeedbacksignaltoaninternal0.8Vreference.When the load current increases, the output of the buck and hencethebuckfeedbacksignaldecrease.Thisdecrease causesthepeakinductorcurrenttoincreaseuntiltheaverageinductorcurrentmatchestheloadcurrent.Whilethe mainswitchisoff,thesynchronousswitchisturnedon untileithertheinductorcurrentstartstoreversedirection orthebeginningofanewclockcycle. WhentheMODEpinisdriventoalogiclow,theLTC3541-2 buckregulatoroperatesinBurstModeoperationforhigh efficiency.Inthismode,themainswitchoperatesbased upon load demand. In Burst Mode operation the peak inductorcurrentissettoafixedvalue,whereeachburst eventcanlastfromafewclockcyclesatlightloadsto nearly continuous cycling at moderate loads. Between bursteventsthemainswitchandanyunneededcircuitry areturnedoff,reducingthequiescentcurrent.Inthissleep state,theloadisbeingsuppliedsolelyfromtheoutput capacitor.Astheoutputvoltagedroops,aninternalerror amplifier'soutputrisesuntilawakethresholdisreached causingthemainswitchtoagainturnon.Thisprocess repeatsataratethatisdependantupontheloadcurrent demand.
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OPERATIO
LTC3541-2
WhentheMODEpinisdriventoalogichightheLTC3541-2 operatesinPulse-Skipmodeforlowoutputvoltageripple. In this mode, the LTC3541-2 continues to switch at a constantfrequencydowntoverylowcurrents,whereit willbeginskippingpulsesusedtocontrolthemain(top) switchtomaintaintheproperaverageinductorcurrent. If the input supply voltage is decreased to a value approachingtheoutputvoltage,thedutycycleofthebuck isincreasedtowardmaximumon-timeand100%duty cycle.Theoutputvoltagewillthenbedeterminedbythe input voltage minus the voltage drop across the main switchandtheinductor. VLDO/Linear Regulator Loop IntheLTC3541-2,theVLDOandlinearregulatorloops consist of an amplifier and N-channel MOSFET output stagesthatservotheoutputtomaintainaregulatoroutput voltage,LVOUT.Theinternalreferencevoltageprovidedto theamplifieris0.4Vallowingforawiderangeofoutput voltages.LoopconfigurationsenablingtheVLDOorthe linearregulatorarestablewithanoutputcapacitanceas lowas2.2Fandashighas100F.BoththeVLDOand thelinearregulatorsarecapableofoperatingwithaninput voltage,VIN,aslowas2.9V. TheVLDOregulatorisdesignedtoprovideupto300mA ofoutputcurrentataverylowLVINtoLVOUTvoltage.This allowsaclean,secondary,analogsupplyvoltagetobe providedwithaminimumdropinefficiency.TheVLDO regulatorisprovidedwiththermalprotectionthatisdesignedtodisabletheVLDOfunctionwhentheoutput,pass transistor'sjunctiontemperaturereachesapproximately 160C. In addition to thermal protection, short-circuit detectionisprovidedtodisabletheVLDOfunctionwhena short-circuitconditionissensed.Thiscircuitisdesigned suchthatanoutputcurrentofapproximately1Acanbe providedbeforethiscircuitwilltrigger.Asdetailedinthe ElectricalCharacteristics,theVLDOregulatorwillbeout ofregulationwhenthiseventoccurs.Boththethermal andshort-circuitfaults,whendetected,aretreatedas catastrophic fault conditions. The LTC3541-2 will be resetuponthedetectionofeitherevent.
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TheN-channelMOSFET,incorporatedintheVLDOregulator,hasitsdrainconnectedtotheLVINpinasshownin Figure1.Toensurereliableoperation,theLVINvoltage mustbestablebeforetheVLDOregulatorisenabled.For thecasewherethevoltageontheLVINpinissuppliedby thebuckregulator,theinternalpowersupplysequencinglogicassuresvoltagesareappliedintheappropriate manner.Forthecasewhereanexternalsupplyisusedto powertheLVINpin,theexternallysuppliedLVINvoltage mustbestable1msbeforetheENVLDOisbroughtfrom alowtoahigh.Further,theexternallysuppliedLVINmust bereducedinconjunctionwithVINwheneverVINispulled loworremoved. Thelinearregulatorisdesignedtoprovidealoweroutput currentthanthatavailablefromtheVLDOregulator.The linearregulator'soutput,passtransistorhasitsdraintied totheVINrail.Thisallowsthelinearregulatortobeturned onpriorto,andindependentof,thebuckregulatorwhich ordinarilydrivestheVLDOregulator.Thelinearregulator isprovidedwiththermalprotectionthatisdesignedto disablethelinearregulatorfunctionwhentheoutputpass transistor'sjunctiontemperaturereachesapproximately 160C. In addition to thermal protection, short-circuit detectionisprovidedtodisablethelinearregulatorfunctionwhenashort-circuitconditionissensed.Thiscircuit isdesignedsuchthatanoutputcurrentofapproximately 120mAcanbeprovidedbeforethiscircuitwilltrigger.As detailedintheElectricalCharacteristics,thelinearregulator willbeoutofregulationwhenthiseventoccurs.Boththe thermalandshort-circuitfaultsaretreatedascatastrophic faultconditions.TheLTC3541-2willberesetuponthe detectionofeitherevent. TheN-channelMOSFET,incorporatedinthelinearregulator,hasitsdrainconnectedtotheVINpinasshownin Figure1.ThesizeoftheseMOSFETsandtheirassociated powerbussingisdesignedtoaccomodate30mAofDC current.Currentsabovethisvaluecanbesupportedfor short periods as stipulated in the Absolute Maximum Ratings.
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OPERATIO
LTC3541-2
TransitioningfromlinearregulatormodetoVLDOmode, accomplishedbybringingENBUCKfromalogiclowtoa logichighwhileENVLDOisalogichigh,isdesignedtobe asseamlessandtransientfreeaspossible.Theprecise transient response of LVOUT due to this transition is a functionofCOUTandtheloadcurrent.Waveformsgiven intheTypicalPerformanceCharacteristicssectionshow typicaltransientresponsesusingtheminimumCOUTof 2.2Fandloadcurrentsof1mAand30mArespectively. Generally, the amplitude of any transients present will decreaseasCOUTisincreased.Toensurereliableoperation andadherencetotheloadregulationlimitspresentedin theElectricalCharactersticstable,theloadcurrentmust notexceedthelinearregulatorIOUTlimitof30mAwithin 20msafterENBUCKhastransitionedtoalogichigh.The 300mA IOUT limit of VLDO applies thereafter. Further, forconfigurationsthatdonotusetheLTC3541-2'sbuck regulatortoprovidetheVLDOinputvoltage(LVIN),theuser mustensureastableLVINvoltageispresentnolessthan 1mspriortoENBUCKtransitioningtoalogichigh.
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In a similar manner, transitioning from VLDO mode to linearregulatormode,accomplishedbybringingENBUCK fromahighlowtoalogiclowwhileENVLDOisalogic high,isdesignedtobeasseamlessandtransientfreeas possible.Again,theprecisetransientresponseofLVOUT duetothistransitionisafunctionofCOUTandtheload current. Waveforms given in the Typical Performance Characteristicssectionshowtypicaltransientresponses usingtheminimumCOUTof2.2Fandloadcurrentsof 1mAand30mArespectively.Generally,theamplitudeof anytransientspresentwilldecreaseasCOUTisincreased. Toensurereliableoperationandadherencetotheload regulationlimitspresentedintheElectricalCharacterstics table,theloadcurrentmustnotexceedthelinearregulator IOUTlimitof30mA1mspriortoENBUCKtransitioningto alogiclowandthereafer.Further,forconfigurationsthat donotusetheLTC3541-2'sbuckregulatortoprovidethe VLDOinputvoltage(LVIN),theusermustcontinuetoensure astableLVINvoltagenolessthan1msafterENBUCKhas transitionedtoalogiclow.
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OPERATIO
LTC3541-2
ThebasicLTC3541-2applicationcircuitisshownonthe firstpageofthisdatasheet.Externalcomponentselection isdrivenbytheloadrequirementandrequirestheselection ofL,followedbyCIN,COUTandtheselectionoftheoutput capacitorfortheVLDOandlinearregulator. BUCK REGULATOR Inductor Selection Formostapplications,theappropriateinductorvaluewillbe 2.2H.Itsvalueischosenlargelybasedonthedesiredripple currentandburstrippleperformance.Generally,largevalue inductorsreduceripplecurrent,andconversely,smallvalue inductorsproducehigherripplecurrent.HigherVINorVOUT mayalsoincreasetheripplecurrentasshowninEquation 1.Areasonablestartingpointforsettingripplecurrentis IL=200mA(40%of500mA). IL = V 1 VOUT 1- OUT VIN ( f )(L ) (1)
TheDCcurrentratingoftheinductorshouldbeatleast equaltothemaximumloadcurrentplushalftheripple currenttopreventcoresaturation.Thus,a600mArated inductorshouldbeenoughformostapplications(500mA +100mA).Forbetterefficiency,choosealowDCresistanceinductor. Inductor Core Selection Different core materials and shapes will change the size/current and price/current relationship of an inductor.Toroidorshieldedpotcoresinferriteorpermalloy materialsaresmallanddon'tradiatemuchenergy,but generallycostmorethanpowderedironcoreinductors withsimilarelectricalcharacteristics.Thechoiceofwhich styleinductortouseoftendependsmoreonthepricevs sizerequirementandanyradiatedfield/EMIrequirements ratherthanwhattheLTC3541-2requirestooperate.Table2 showssometypicalsurfacemountinductorsthatwork wellinLTC3541-2applications.
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Table 2. Representative Surface Mount Inductors
PART NUMBER Sumida CDRH3D23 VALUE (H) 1.0 1.5 2.2 3.3 2.2 3.3 1.0 1.5 2.2 3.3 1.0 2.2 DCR MAX DC ( MAX) CURRENT (A) 0.025 0.029 0.038 0.048 0.116 0.174 0.058 0.068 0.104 0.138 0.060 0.097 2 1.65 1.3 1.1 0.950 0.770 2.7 2.2 1.8 1.3 1.00 0.79 SIZE W x L x H (mm3) 3.9x3.9x2.4 Sumida CMD4D06 Coilcraft ME3220 3.5x4.3x0.8 2.5x3.2x2.0 Murata LQH3C 2.5x3.2x2.0
APPLICATIO S I FOR ATIO W U U
CIN and COUT Selection Incontinuousmode,thesourcecurrentofthetopMOSFET isasquarewaveofdutycycleVOUT/VIN.Topreventlarge voltagetransients,alowESRinputcapacitorsizedforthe maximumRMScurrentmustbeused.ThemaximumRMS capacitorcurrentisgivenby: cIN required IRMS IOMAX VOUT ( VIN - VOUT ) VIN
1/2 2
This formula has a maximum at VIN = 2VOUT, where IRMS=IOUT/2.Thissimple,worst-caseconditioniscommonly used for design. Note that the capacitor manufacturer'sripplecurrentratingsareoftenbasedon2000 hoursoflife.Thismakesitadvisabletofurtherderatethe capacitororchooseacapacitorratedatahighertemperaturethanrequired.Alwaysconsultthemanufacturerwith anyquestionregardingpropercapacitorchoice. TheselectionofCOUTforthebuckregulatorisdrivenby thedesiredbucklooptransientresponse,requiredeffective seriesresistance(ESR)andburstrippleperformance. TheLTC3541-2minimizestherequirednumberofexternal componentsbyprovidinginternalloopcompensationfor thebuckregulatorloop.Loopstability,transientresponse andburstrippleperformancecanbetailoredbychoice ofoutputcapacitance.Formanyapplications,desirable
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LTC3541-2
stability,transientresponseandrippleperformancecan be obtained by choosing an output capacitor value of 10Fto22F. Typically,oncetheESRrequirementforCOUThasbeen met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. The output ripple VOUT is determinedby: 1 VOUT IL ESR + 8 fcOUT wheref=operatingfrequency,COUT=outputcapacitance andIL=ripplecurrentintheinductor.Forafixedoutput voltage,theoutputrippleishighestatmaximuminput voltagesinceILincreaseswithinputvoltage. Aluminumelectrolyticanddrytantalumcapacitorsareboth availableinsurfacemountconfigurations.Inthecaseof tantalum,itiscriticalthatthecapacitorsaresurgetested foruseinswitchingpowersupplies.Anexcellentchoiceis theAVXTPSseriesofsurfacemounttantalum.Theseare speciallyconstructedandtestedforlowESRsotheygive thelowestESRforagivenvolume.Othercapacitortypes includeSanyoPOSCAP,KemetT510andT495series,and Sprague593Dand595Dseries.Consultthemanufacturer forotherspecificrecommendations. Using Ceramic Input and Output Capacitors Highvalue,lowcostceramiccapacitorsarenowbecoming availableinsmallercasesizes.Theirhighripplecurrent, high voltage rating, and low ESR make them ideal for switchingregulatorapplications.SincetheLTC3541-2's controlloopdoesnotdependontheoutputcapacitor'sESR forstableoperation,ceramiccapacitorscanbeusedfreely toachieveverylowoutputrippleandsmallcircuitsize. However, care must be taken when ceramic capacitors are used at the input and the output. When a ceramic capacitorisusedattheinputandthepowerissupplied
byawalladapterthroughlongwires,aloadstepatthe outputcaninduceringingattheinput,VIN.Atbest,this ringingcancoupletotheoutputandbemistakenasloop instability.Atworst,asuddeninrushofcurrentthrough thelongwirescanpotentiallycauseavoltagespikeatVIN, largeenoughtodamagethepart.
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Whenchoosingtheinputandoutputceramiccapacitors, choose the X5R or X7R dielectric formulations. These dielectricshavethebesttemperatureandvoltagecharacteristicsofalltheceramicsforagivenvalueandsize.
Checking Transient Response Theregulatorloopresponsecanbecheckedbylooking attheloadtransientresponse.Switchingregulatorstake severalcyclestorespondtoastepinloadcurrent.When aloadstepoccurs,VOUTimmediatelyshiftsbyanamount equalto(ILOAD*ESR),whereESRistheeffectiveseries resistanceofCOUT.ILOADalsobeginstochargeordischargeCOUT,whichgeneratesafeedbackerrorsignal.The regulatorloopthenactstoreturnVOUTtoitssteady-state value.DuringthisrecoverytimeVOUTcanbemonitored for overshoot or ringing that would indicate a stability problem.Foradetailedexplanationofswitchingcontrol looptheoryseeApplicationNote76. Asecond,moreseveretransientiscausedbyswitching inloadswithlarge(>1F)supplybypasscapacitors.The dischargedbypasscapacitorsareeffectivelyputinparallelwithCOUT,causingarapiddropinVOUT.Noregulator candeliverenoughcurrenttopreventthisproblemifthe loadswitchresistanceislowanditisdrivenquickly.The onlysolutionistolimittherisetimeoftheswitchdrive so that the load rise time is limited to approximately (25*CLOAD).Thus,a10Fcapacitorchargingto3.3V would require a 250s rise time, limiting the charging currenttoabout130mA. VLDO/LINEAR REGULATOR Output Capacitance and Transient Response TheLTC3541-2isdesignedtobestablewithawiderange ofceramicoutputcapacitors.TheESRoftheoutputcapacitoraffectsstability,mostnotablywithsmallcapacitors.A minimumoutputcapacitorof2.2FwithanESRof0.05 orlessisrecommendedtoensurestability.TheLTC3541-2 VLDOisamicropowerdeviceandoutputtransientresponse will be a function of output capacitance. Larger values ofoutputcapacitancedecreasethepeakdeviationsand provideimprovedtransientresponseforlargerloadcurrent
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APPLICATIO S I FOR ATIO W U U
LTC3541-2
changes.Notethatbypasscapacitorsusedtodecouple individual components powered by the LTC3541-2 will increasetheeffectiveoutputcapacitorvalue.HighESR tantalum and electrolytic capacitors may be used, but alowESRceramiccapacitormustbeinparallelatthe output.ThereisnominimumESRormaximumcapacitor sizerequirement. Extraconsiderationmustbegiventotheuseofceramic capacitors.Ceramiccapacitorsaremanufacturedwitha varietyofdielectrics,eachwithdifferentbehavioracross temperature and applied voltage. The most common dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U
20 0 cHANGE IN VALUE (%) -20 -40 -60 -80 -100 BOTH cAPAcITORS ARE 1F, 10V, 0603 cASE SIZE X5R
Y5V
0
2
6 4 Dc BIAS VOLTAGE (V)
8
10
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Figure 6. Change in Capacitor vs Bias Voltage
20 0 cHANGE IN VALUE (%) X5R -20 Y5V -40 -60 -80
BOTH cAPAcITORS ARE 1F, 10V, 0603 cASE SIZE -100 -50 0 25 50 -25 TEMPERATURE (c)
75
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Figure 7. Change in Capacitor vs Temperature
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andY5Vdielectricsaregoodforprovidinghighcapacitancesinasmallpackage,butexhibitlargevoltageand temperature coefficients as shown in Figures 6 and 7. Whenusedwitha2Vregulator,a1FY5Vcapacitorcan loseasmuchas75%ofitsinitialcapacitanceoverthe operatingtemperaturerange.TheX5RandX7Rdielectrics resultinmorestablecharacteristicsandareusuallymore suitableforuseastheoutputcapacitor.TheX7Rtypehas betterstabilityacrosstemperature,whiletheX5Risless expensiveandisavailableinhighervalues.Inallcases, theoutputcapacitanceshouldneverdropbelow1For instabilityordegradedperformancemayoccur. EFFICIENCY CONSIDERATIONS Generally,theefficiencyofaregulatorisequaltotheoutputpowerdividedbytheinputpowertimes100%.Itis oftenusefultoanalyzeindividuallosstermstodetermine whichtermsarelimitingefficiencyandwhatifanychange wouldyieldthegreatestimprovement.Efficiencycanbe expressedas: Efficiency=100%-(L1+L2+L3+...) whereL1,L2,etc.aretheindividuallosstermsasapercentageofinputpower. Althoughalldissipativeelementsinthecircuitproduce losses,threemainsourcestypicallyaccountforthemajorityofthelossesintheLTC3541-2circuits:VINquiescent current,I2Rlosses,andlossacrossVLDOoutputdevice. WhenoperatingwithboththebuckandVLDOregulator active (ENBUCK and ENVLDO equal to logic high), VIN quiescentcurrentlossandlossacrosstheVLDOoutput devicedominatetheefficiencylossatlowloadcurrents, whereastheI2RlossandlossacrosstheVLDOoutput devicedominatetheefficiencylossatmediumtohighload currents.Atlowloadcurrentswiththepartoperatingwith thelinearregulator(ENBUCKequaltologiclow,ENVLDO equaltologichigh),efficiencyistypicallydominatedby thelossacrossthelinearregulatoroutputdeviceandVIN quiescentcurrent.Inatypicalefficiencyplot,theefficiency curveatverylowloadcurrentscanbemisleadingsince theactualpowerlostisoflittleconsequence.
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APPLICATIO S I FOR ATIO W U U
LTC3541-2
1.TheVINquiescentcurrentlossinthebuckisduetotwo components:theDCbiascurrentasgivenintheElectrical Characteristicsandtheinternalmainswitchandsynchronousswitchgatechargecurrents.Thegatechargecurrent resultsfromswitchingthegatecapacitanceoftheinternal powerswitches.Eachtimethegateisswitchedfromhigh tolowtohighagain,apacketofcharge,dQ,movesfrom VINtoground.TheresultingdQ/dtisthecurrentoutof VINthatistypicallylargerthantheDCbiascurrentand proportionaltofrequency.BoththeDCbiasandgatecharge lossesareproportionaltoVINandthustheireffectswill bemorepronouncedathighersupplyvoltages. 2.I2Rlossesarecalculatedfromtheresistancesofthe internalswitches,RSW,andexternalinductorRL.Incontinuousmode,theaverageoutputcurrentflowingthrough inductorLis"chopped"betweenthemainswitchandthe synchronousswitch.Thus,theseriesresistancelooking into the SW pin is a function of both top and bottom MOSFETRDS(ON)andthedutycycle(DC)asfollows: RSW=(RDS(ON)TOP)(DC)+(RDS(ON)BOT)(1-DC) TheRDS(ON)forboththetopandbottomMOSFETscan beobtainedfromtheTypicalPerformanceCharacteristics curves. Thus, to obtain I2R losses, simply add RSW to RLandmultiplytheresultbythesquareoftheaverage outputcurrent. 3.LossesintheVLDO/linearregulatorareduetotheDCbias currentsasgivenintheElectricalCharacteristicsandtothe (VIN-VOUT)voltagedropacrosstheinternaloutputdevice transistor. Other losses when the buck and VLDO regulator are in operation (ENBUCK and ENVLDO equal logic high), includingCINandCOUTESRdissipativelossesandinductorcorelosses,generallyaccountforlessthan2%total additionalloss.
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THERMAL CONSIDERATIONS The LTC3541-2 requires the package backplane metal (GNDpin)tobewellsolderedtothePCboard.Thisgives the DFN package exceptional thermal properties. The power handling capability of the device will be limited by the maximum rated junction temperature of 125C. TheLTC3541-2hasinternalthermallimitingdesignedto protectthedeviceduringmomentaryoverloadconditions. Forcontinuousnormalconditions,themaximumjunction temperatureratingof125Cmustnotbeexceeded.Itis importanttogivecarefulconsiderationtoallsourcesof thermalresistancefromjunctiontoambient.Additional heatsourcesmountednearbymustalsobeconsidered. Forsurfacemountdevices,heatsinkingisaccomplished byusingtheheat-spreadingcapabilitiesofthePCboard anditscoppertraces.Copperboardstiffenersandplated throughholescanalsobeusedtospreadtheheatgeneratedbypowerdevices. ToavoidtheLTC3541-2exceedingthemaximumjunction temperature,somethermalanalysisisrequired.Thegoal ofthethermalanalysisistodeterminewhetherthepower dissipatedexceedsthemaximumjunctiontemperatureof thepart.Thetemperatureriseisgivenby: TR=PD*JA wherePDisthepowerdissipatedbytheregulatorandJA isthethermalresistancefromthejunctionofthedieto theambienttemperature. Thejunctiontemperature,TJ,isgivenby: TJ=TA+TR whereTAistheambienttemperature.
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APPLICATIO S I FOR ATIO W U U
LTC3541-2
As an example, consider the LTC3541-2 with an input voltageVINof2.9V,anLVINvoltageof1.875V,anLVOUT voltageof1.5V,aloadcurrentof300mAfortheVLDO regulator, a load current of 200mA for the buck (total load for buck = 500mA), and an ambient temperature of85C.Fromthetypicalperformancegraphofswitch resistance,theRDS(ON)oftheP-channelswitchat85Cis approximately0.25.TheRDS(ON)oftheN-channelswitch isapproximately0.4.Therefore,powerdissipatedbythe partisapproximately: PD=(ILOADBUCK)2*RSW+(ILOADVLDO)* (LVIN-LVOUT)=188mW Forthe3mmx3mmDFNpackage,theJAis43C/W. Thus,thejunctiontemperatureoftheregulatoris: TJ=85C+(0.188)(43)=93C whichiswellbelowthemaximumjunctiontemperature of125C. Notethatathighersupplyvoltages,thejunctiontemperatureislowerduetoreducedswitchresistanceRDS(ON). PC BOARD LAYOUT CHECKLIST Whenlayingouttheprintedcircuitboard,thefollowing checklistshouldbeusedtoensureproperoperationofthe LTC3541-2.Checkthefollowinginyourlayout: 1.Thepowertraces,consistingoftheGNDtrace,theSW traceandtheVINtraceshouldbekeptshort,directand wide. 2.Doesthe(+)plateofCINconnecttoVINascloselyas possible?ThiscapacitorprovidestheACcurrenttothe internalpowerMOSFETs. 3.Keeptheswitchingnode,SW,awayfromthesensitive LFBnode. 4. Keep the (-) plates of CIN and COUT as close as possible.
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DESIGN EXAMPLE Asadesignexample,assumetheLTC3541-2isusedin asinglelithium-ionbatterypoweredcellularphoneapplication.TheVINwillbeoperatingfromamaximumof 4.2Vdowntoabout2.9V.Theloadcurrentrequirement isamaximumof0.5Aforthebuckoutputbutmostof thetimeitwillbeinstandbymode,requiringonly2mA. Efficiencyatbothlowandhighloadcurrentsisimportant. Theoutputvoltageforthebuckis1.875V.TherequirementfortheoutputoftheVLDOregulatoris1.5Voutput voltagewhileprovidingupto0.3Aofcurrent.Withthis informationwecancalculateLusingEquation2: L= V 1 VOUT 1- OUT VIN ( f )( IL ) (2) SubstitutingVOUT=1.875V,VIN=3.55V(typ),IL=200mA andf=2.25MHzinEquation3gives: L= 1.8 V 1.8 V (3) 1- 3.45V = 1.91H 2.25MHz(200mA) A2.2Hinductorworkswellforthisapplication.Forbest efficiencychoosea600mAorgreaterinductorwithless than0.2seriesresistance. CINwillrequireanRMScurrentratingofatleast0.25A = ILOAD(MAX)/2 at temperature . COUT for the buck is chosentohaveavalueof22FandanESRoflessthan 0.25. In most cases, a ceramic capacitor will satisfy thisrequirement. COUTfortheVLDOregulatorischosenas2.2F.
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APPLICATIO S I FOR ATIO W U U
LTC3541-2 TYPICAL APPLICATIO S
Dual Output with Minimal External Components Using Auto Start-Up Sequence, Buck in Burst Mode Operation for High Efficiency Down to Low Load Currents
VIN 2.9V TO 4.2V VOUT 1V/DIV LVOUT 1V/DIV VIN 2V/DIV
SW 2.2H
ENVLDO
VIN MODE LTC3541-2 ENBUCK GND VOUT LVIN 10F LVOUT PGND VOUT2 1.5V 300mA
VOUT1 1.875V 200mA
Dual Output with Minimal External Components Using Auto-Start-Up Sequence, Buck in Pulse-Skip Mode for Low Noise Operation
VIN 2.9V TO 4.2V VOUT 1V/DIV
SW 2.2H
ENVLDO
VIN MODE LTC3541-2 ENBUCK GND VOUT LVIN 10F LVOUT PGND VOUT2 1.5V 300mA
VOUT1 1.875V 200mA
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2.2F
35412 TA02a
IVOUT = 200mA ILVOUT = 300mA
2ms/DIV
35412TA02b
LVOUT 1V/DIV VIN 2V/DIV
2.2F
35412 TA03a
IVOUT = 200mA ILVOUT = 300mA
2ms/DIV
35412TA03b
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LTC3541-2 TYPICAL APPLICATIO S
Dual Output Using Minimal External Components with VOUT2 Controlled by External Logic Signal, Buck in Burst Mode Operation for High Efficiency Down to Low Load Currents
VIN 2.9V TO 4.2V VOUT 1V/DIV
SW 2.2H
ENVLDO
VIN MODE LTC3541-2 ENBUCK GND VOUT LVIN 10F LVOUT PGND VOUT2 1.5V 300mA
VOUT1 1.875V 200mA
Dual Output Using Minimal External Components with VOUT1 Controlled by External Logic Signal, Buck in Burst Mode Operation for High Efficiency Down to Low Load Currents
VIN 2.9V TO 4.2V VOUT 1V/DIV SW 2.2H ENVLDO LVOUT 1V/DIV VIN 2V/DIV VIN MODE LTC3541-2 ENBUCK GND VOUT LVIN LVOUT PGND VOUT2 1.5V 2.2F 300mA
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VOUT1 1.875V 200mA 10F
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LVOUT 1V/DIV VIN 2V/DIV
2.2F
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IVOUT = 200mA ILVOUT = 300mA
4ms/DIV
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IVOUT = 200mA ILVOUT = 30mA
4ms/DIV
35412TA05b
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LTC3541-2 U
DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTc DWG # 05-08-1699)
0.675 0.05 PAcKAGE OUTLINE 0.25 0.05 0.50 BSc 2.38 0.05 (2 SIDES) R = 0.115 TYP 6 0.38 0.10 10 3.00 0.10 (4 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES) BOTTOM VIEW--EXPOSED PAD 1 1.65 0.10 (2 SIDES)
(DD10) DFN 1103
PACKAGE DESCRIPTIO
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES)
RECOMMENDED SOLDER PAD PITcH AND DIMENSIONS
0.25 0.05 0.50 BSc
0.00 - 0.05
NOTE: 1. DRAWING TO BE MADE A JEDEc PAcKAGE OUTLINE M0-229 VARIATION OF (WEED-2). cHEcK THE LTc WEBSITE DATA SHEET FOR cURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO ScALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PAcKAGE DO NOT INcLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXcEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENcE FOR PIN 1 LOcATION ON THE TOP AND BOTTOM OF PAcKAGE
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Information furnished by Linear Technology corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3541-2 RELATED PARTS
PART NUMBER LT 3023
(R)
DESCRIPTION Dual,2x100mA,LowNoiseMicropowerLDO
COMMENTS VIN:1.8Vto20V,VOUT(MIN)=1.22V,VDO=0.30V,IQ=40A,ISD<1A, VOUT=ADJ,DFN,MSPackages,LowNoise<20VRMS(P-P),Stablewith 1FCeramicCapacitors VIN:1.8Vto20V,VOUT(MIN)=1.22V,VDO=0.30V,IQ=60A,ISD<1A, VOUT=ADJ,DFN,TSSOPPackages,LowNoise<20VRMS(P-P),Stablewith 1FCeramicCapacitors VIN:0.9Vto5.5V,VOUT(MIN)=0.4V,2.7Vto5.5VBiasVoltageRequired, VDO=45mV,IQ=50A,ISD<1A,VOUT=ADJ,DFNPackages,Stablewith 1FCeramicCapacitors 1.5MHzConstantFrequencyCurrentModeOperation,VINfrom2.5Vto 5.5V,VOUTDownto0.6V,DFN,MSPackages 2.25MHzConstantFrequencyCurrentModeOperation,VINfrom2.5Vto 5.5V,VOUTDownto0.6V,DFN,MSPackages 600mA,1.5MHzCurrentModeBuckRegulator,I2CProgrammable VOUTfrom0.85Vto1.55V,two50mALDOs,BackupBatteryInputwith PowerPathControl,QFNPackage VIN:2.7Vto5.5V,VOUT(MIN)Buck=0.8V,VOUT(MIN)VDLO=0.4VOUT(MIN), 14-PinDFNPackage VIN:2.7Vto5.5V,VOUT(MIN)=0.6V,SwitchestoLDOModeat3A, DD8,MS8/EPackages VIN:2.7Vto5.5V,VOUT(MIN)Buck=0.8V,VOUT(MIN)VLDO=0.4V, 3mmx3mm10-PinDFNPackage 95%Efficiency,VIN:2.5Vto5.5V,VOUT(MIN)=0.6V,IQ=40A,ISD<1A, DFNand10-PinMSPackages VINfrom2.65Vto9.8V,ConstantFrequency550kHzOperation
LT3024
Dual,100mA/500mA,LowNoiseMicropowerLDO
LTC3025
300mA,MicropowerVLDOLinearRegulator
LTC3407 LTC3407-2 LTC3445
DualSynchronous600mASynchronousStep-Down DC/DCRegulator DualSynchronous800mASynchronousStep-Down DC/DCRegulator,2.25MHz I2CControllableBuckRegulatorwithTwoLDOsand BackupBatteryInput TripleOutputStep-DownConverter1AOutputBuck, TwoEach300mAVDLOs 600mA(IOUT),HighEfficiency,1.5MHz/2.25MHz SynchronousStep-DownRegulatorwithLDOMode HighEfficiencyBuck+VLDORegulator
LTC3446 LTC3448 LTC3541
LTC3548/LTC3548-1 Dual800mA/400mAIOUT,2.25MHz,Synchronous Step-DownDC/DCConverter LTC3548-2 LTC3700 Step-DownDC/DCControllerwithLDORegulator PowerPathisatrademarkofLinearTechnologyCorporation.
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0 Linear Technology Corporation
1630 Mccarthy Blvd., Milpitas, cA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LT 0407 REV A * PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2006

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