LTC3548

1

3548fc

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

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PDAs/Palmtop PCs

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Digital Cameras

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Cellular Phones

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Portable Media Players

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PC Cards

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Wireless and DSL Modems

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High Efficiency: Up to 95%

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Very Low Quiescent Current: Only 40μA

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2.25MHz Constant-Frequency Operation

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High Switch Current: 0.7A and 1.2A

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No Schottky Diodes Required

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Current Mode Operation for Excellent Line

and Load Transient Response

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Short-Circuit Protected

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Low Dropout Operation: 100% Duty Cycle

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Output Voltages from 5V down to 0.6V

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Power-On Reset Output

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Externally Synchronizable Oscillator

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Small Thermally Enhanced MSOP and 3mm

× 3mm

DFN Packages

Dual Synchronous,

400mA/800mA, 2.25MHz

Step-Down DC/DC Regulator

step down DC/DC converter. Intended for low power ap-

plications, it operates from 2.5V to 5.5V input voltage

range and has a constant 2.25MHz switching frequency,

allowing the use of tiny, low cost capacitors and inductors

with a profile ≤1mm. Each output voltage is adjustable

from 0.6V to 5V. Internal synchronous 0.35Ω, 0.7A/1.2A

power switches provide high efficiency without the need

for external Schottky diodes.

A user selectable mode input is provided to allow the user

to trade-off noise ripple for low power efficiency. Burst

Mode operation provides high efficiency at light loads,

while pulse-skipping mode provides low noise ripple at

light loads.

To further maximize battery runtime, the P-channel

MOSFETs are turned on continuously in dropout (100%

duty cycle), and both channels draw a total quiescent cur-

rent of only 40μA. In shutdown, the device draws <1μA.

Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators

RUN2

TO 5.5V

AT 400mA

AT 800mA

RUN1

POR

SW1

GND

SW2

MODE/SYNC

LTC3548

10μF

100k

RESET

33pF

68pF

2.2μH

4.7μH

887k

604k

301k

280k

4.7μF

10μF

3548 TA01

LOAD CURRENT (mA)

1

100

95

90

85

80

75

70

65

60

1000

100

10

1

0.1

10

100

1000

3548 TA02

Burst Mode OPERATION

CHANNEL 1, NO LOAD ON CHANNEL 2

POWER LOSS

EFFICIENCY

LTC3548 Efficiency Curve

L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective

owners. Protected by U.S. Patents, including 5481178, 6127815, 6304066, 6498466, 6580258

6611131..