LTC3446

1

3446fd

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Monolithic Buck Regulator

with Dual VLDO Regulators

verter with two very low dropout (VLDO) linear regulators

to provide up to three stepped-down output voltages from

a single input voltage. The input voltage range is ideally

suited for Li-Ion battery-powered applications, as well

as powering low voltage logic from 5V or 3.3V rails. The

output voltage range extends down to 0.4V for the VLDO

regulators and 0.8V for the buck.

The 1A synchronous buck converter provides the main

output with high efficiency, typically 85%. The two 300mA

VLDO regulators can run off the main output to provide

two additional lower voltage outputs. A built-in supply

monitor provides a power good indication.

The buck converter switches at 2.25MHz, allowing the use

of small surface mount inductors and capacitors. Constant

frequency current mode operation produces controlled

output spectrum and fast transient response. A mode-

select pin allows automatic Burst Mode operation to be

enabled for higher efficiency at light load, or disabled for

lower noise operation down to very light loads. The two

VLDO regulators are stable with ceramic output capacitors

as small as 1μF.

Buck Efficiency vs Buck Load Current

Single Input Supply

Step-Down Output and Powers Two 300mA

VLDO™ Linear Regulators

all Outputs Enabled

Inductors

High Efficiency at Light Loads

Package

Logic, I/O, FPGAs, CPLDs, ASICs and CPUs

L, 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.

59k

L1

1.8μH

47.5k

SW

BUCKFB

LTC3446

GND

22μF

X7R

1000pF

DIGITAL

CONTROL

22μF

X7R

1.8V

400mA MAX

110k

40.2k

2.2μF

X7R

1.5V

300mA MAX

2.9V TO 5.5V

PGOOD

MODESEL

ENBUCK

ENLDO1

ENLDO2

80.6k

40.2k

2.2μF

X7R

L1: TOKO A960AW-1R8M

3446 TA01

1.2V

300mA MAX

3.3k

LOAD CURRENT (mA)

1

40

50

60

70

80

100

10

100

3446 TA01b

1000

90

Burst Mode

OPERATION

PWM

MODE