LTC3541



3541fa

High Efficiency

Buck + VLDO Regulator

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PDAs/PalmtopPCs

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DigitalCameras

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CellularPhones

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PCCards

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WirelessandDSLModems

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OtherPortablePowerSystems

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Regulator

Auto Start-Up Powers Buck Output Prior to

VLDO/Linear Regulator Output

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Independent High Efficiency, 500mA Buck

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300mA VLDO Regulator with 30mA Standalone Mode

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No External Schottky Diodes Required

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Buck Output Voltage Range: 0.8V to 5V

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VLDO Output Voltage Range VLDO: 0.4V to 4.1V

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SelectableFixedFrequency,Pulse-SkipOperationor

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Short-CircuitProtected

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CurrentModeOperationforExcellentLineandLoad

TransientResponse

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ConstantFrequencyOperation:2.25MHz

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LowDropoutBuckOperation:100%DutyCycle

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Small,ThermallyEnhanced,10-Lead(3mm

×3mm)

DFNPackage

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

, LT, LTc and LTM 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

converterwithaverylowdropoutlinearregulator

(VLDO)toprovideuptotwooutputvoltagesfromasingle

inputvoltagewithminimalexternalcomponents.When

configuredfordualoutputoperation,theLTC3541’sauto

start-upfeaturewillbringtheBuckoutputintoregulation

inacontrolledmannerpriortoenablingtheVLDOregulator

outputwithouttheneedforexternalpincontrol.VLDO/

linearregulatoroutputpriortoBuckoutputsequencing

mayalsobeobtainedviaexternalpincontrol.Theinput

voltagerangeisideallysuitedforLi-Ionbattery-powered

applications,aswellaspoweringsub-3.3Vlogicfrom5V

or3.3Vrails.

Thesynchronousbuckconverterprovidesahighefficiency

output,typically90%,capableofprovidingupto500mA

ofcontinuousoutputcurrentwhileswitchingat2.25MHz,

allowingtheuseofsmallsurfacemountinductorsandca-

pacitors.Amode-selectpinallowsBurstModeoperation

tobeenabledforhigherefficiencyatlightloadcurrents,or

disabledforlowernoise,constantfrequencyoperation.

TheVLDOregulatorprovidesalownoise,lowvoltage

outputcapableofprovidingupto300mAofcontinuous

outputcurrentusingonlya2.2µFceramiccapacitor.The

comefromthebuckregulatororaseparatesupply.

SW

ENBUCK

BUCKFB

ENVLDO

MODE

GND

LFB

PGND

LTC3541

150k

1.5V

300mA

2.2

µF

115k

3541 TA01a

2.2

µH

10

µF

2.9V TO 5.5V

243k

22pF

412k

2.5V

200mA

LTC3541 Typical Application

Buck (Burst) Efficiency and Power Loss vs Load Current

LOAD CURRENT (mA)

1

40

50

60

70

80

10

100

1000

3541 TA01b

30

20

10

0

90

100

0.001

0.01

0.1

0.0001

1

EFFICIENCY

POWER LOSS