LTC3549

1

3549f

LOAD CURRENT (mA)

30

90

100

20

10

80

50

70

60

40

0.1

10

100

1k

3549 TA02

0

1

0.1

0.01

0.001

0.0001

1

POWER LOST

Regulator in 2mm × 3mm DFN

buck regulator using a constant-frequency, current mode

architecture. The output voltage is adjusted via an external

resistor divider.

A fixed switching frequency of 2.25MHz is supported.

This switching frequency allows the use of small surface

mount inductors and capacitors, including ceramics.

Supply current during Burst Mode operation is only 50µA

dropping to < 1µA in shutdown. The 1.6V to 5.5V input

voltage range makes the LTC3549 ideally suited for single

cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd or NiMH

battery-powered applications. 100% duty cycle capabil-

ity provides low dropout operation, extending battery

life in portable systems. Burst Mode operation can be

user-enabled, increasing efficiency at light loads, further

extending battery life.

The internal synchronous switch increases efficiency and

eliminates the need for an external Schottky diode. Internal

soft-start offers controlled output voltage rise time at start-

up without the need for external components.

■

2 AA-Cell Applications

■

Cellular Phones

■

Digital Cameras

■

MP3 Players

■

1.6V to 5.5V Input Voltage Range

■

Internal Soft-Start

■

■

2.25MHz Constant-Frequency Operation

■

High Efficiency: Up to 93%

■

■

450mA Peak Inductor Current

■

No Schottky Diode Required

■

Low Dropout Operation: 100% Duty Cycle

■

0.611V Reference Voltage

■

Stable with Ceramic Capacitors

■

Shutdown Mode Draws <1µA Supply Current

■

Current Mode Operation for Excellent Line and Load

Transient Response

■

Overtemperature Protection

■

Available in a Low Profile (0.75mm) 6-Lead

(2mm x 3mm) DFN Package

High Efficiency Step-Down Converter

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

Burst Mode is a registered trademark of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Protected by U.S. Patents,

including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131.

RUN

MODE

SW

GND

LTC3549

3.3

1.5V

200k

4.7

CER

*TDK VLF3012AT-3R3MR87

1.8V TO

5.5V

137k

3549 TA01

22pF

4.7

CER