General Description

The MAX1920/MAX1921 step-down converters deliver

over 400mA to outputs as low as 1.25V. These converters

use a unique proprietary current-limited control scheme

that achieves over 90% efficiency. These devices maintain

extremely low quiescent supply current (50μA), and their

high 1.2MHz (max) operating frequency permits small,

low-cost external components. This combination makes

the MAX1920/MAX1921 excellent high-efficiency alterna-

tives to linear regulators in space-constrained applications.

Internal synchronous rectification greatly improves effi-

ciency and eliminates the external Schottky diode required

in conventional step-down converters. Both devices also

include internal digital soft-start to limit input current upon

startup and reduce input capacitor requirements.

The MAX1920 provides an adjustable output voltage

(1.25V to 4V). The MAX1921 provides factory-preset

output voltages (see the Selector Guide). Both are

available in space-saving 6-pin SOT23 packages. The

MAX1920 is also available in a 6-pin TDFN package.

Applications

● Next-Generation Wireless Handsets

● PDAs, Palmtops, and Handy-Terminals

● Battery-Powered Equipment

● CDMA Power Amplifier Supply

Features

● 400mA Guaranteed Output Current

● Internal Synchronous Rectifier for > 90% Efficiency

● Tiny 6-Pin SOT23 Package

● Available in 6-Pin TDFN Package (MAX1920)

● Up to 1.2MHz Switching Frequency for Small

External Components

● 50μA Quiescent Supply Current

● 0.1μA Logic-Controlled Shutdown

● 2V to 5.5V Input Range

● Fixed 1.5V, 1.8V, 2.5V, 3V, and 3.3V Output

Voltages (MAX1921)

● Adjustable Output Voltage (MAX1920)

● ±1.5% Initial Accuracy

● Soft-Start Limits Startup Current

19-2296; Rev 3; 8/05

Note: The MAX1921 offers five preset output voltage options.

See the Selector Guide, and then insert the proper designator

into the blanks above to complete the part number.

+Denotes a lead-free package.

Ordering Information

MAX1921

IN

AGND

SHDN

LX

PGND

OUT

OFF

ON

4.75kΩ

4.7µF

4.7µH

5600pF

OUTPUT

1.5V UP TO 400mA

INPUT

2V TO 5.5V

AGND

OUT (FB)

SHDN

1

6 LX

5 PGND

IN

MAX1920

MAX1921

MAX1920

SOT23-6

TOP VIEW

2

3

4

( ) ARE FOR MAX1920 ONLY

A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.

1

2

3

6

5

4

TDFN

•

•

Typical Operating Circuit

Pin Configuration

PART

TEMP RANGE

PIN-PACKAGE

MAX1920EUT-T

-40°C to +85°C

6 SOT23-6

MAX1920EUT+T

-40°C to +85°C

6 SOT23-6

MAX1920ETT-T

-40°C to +85°C

6 TDFN

MAX1920ETT+T

-40°C to +85°C

6 TDFN

MAX1921EUT_ _-T

-40°C to +85°C

6 SOT23-6

MAX1921EUT_ _+T

-40°C to +85°C

6 SOT23-6

MAX1920/MAX1921

Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23