LTC3541-3



35413fc

High Efficiency

Buck + VLDO Regulator

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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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High Efficiency 500mA Buck Plus 300mA VLDO

Regulator

Auto Start-Up Powers VLDO/Linear Regulator

Output Prior to Buck Output

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Independent 500mA High Efficiency 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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FixedBuck Output Voltage: 1.8V

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FixedVLDO Output Voltage: 1.575V

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SelectableFixedFrequency,Pulse-SkipOperation

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Short-CircuitProtected

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CurrentModeOperationforExcellentLineandLoad

TransientResponse

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ShutdownCurrent:<3

µA

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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, 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.

DCconverterwithaverylowdropoutlinearregulator

toprovidetwooutputvoltagesfromasingleinputvoltage

withminimumexternalcomponents.Whenconfigured

fordualoutputoperation,theLTC3541-3’sautostart-up

featurewillbringthe1.575VVLDO/linearregulatoroutput

intoregulationinacontrolledmannerpriortoenablingthe

1.8Vbuckoutputwithouttheneedforexternalpincontrol.

The300mAVLDO/linearregulatoroutputwillsourceonly

30mAuntilthebuckoutputachievesregulation.Theinput

voltagerangeisideallysuitedforapplicationspowered

fromaLi-Ionbatteryand5Vor3.3Vrails.

Thesynchronousbuckconverterprovidesahighefficiency

output,typically90%.Itcanprovideupto500mAofoutput

currentwhileswitchingat2.25MHz,allowingtheuseof

smallsurfacemountinductorsandcapacitors.Amode

selectpinallowsBurstModeoperationtobeenabledfor

higherefficiencyatlightloadcurrents,ordisabledforlower

noise,constantfrequencyoperation.

TheVLDOregulatorprovidesalownoise,lowvoltage

outputcapableofprovidingupto300mAofoutputcurrent

usingonlya2.2

µFceramiccapacitor.Theinputsupply

buckregulatororaseparatesupply.

LTC3541-3 Typical Application

SW

ENBUCK

ENVLDO

MODE

GND

PGND

LTC3541-3

1.575V

2.2

µF

35413 TA01a

2.2

µH

10

µF

3V TO 5V

1.8V

Buck (Burst) Efficiency vs Load Current

LOAD CURRENT (mA)

30

90

100

20

10

80

50

70

60

40

1

10

100

1000

35413 TA01b

0

0.1

1

0.001

0.01

0.0001

EFFICIENCY

POWER

LOSS