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MAX1921EUT18T

Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23

Maxim Integrated 

MAX1920/MAX1921

Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

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

Typical Operating Circuit

INPUT

2V TO 5.5V

CIN

IN

LX

MAX1921

AGND

PGND

ON

SHDN

OUT

OFF

4.7µH

OUTPUT

1.5V UP TO 400mA

4.75kΩ

5600pF

4.7µF

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

Ordering Information

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

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.

Pin Configuration

TOP VIEW

•

IN 1

6 LX

MAX1920

AGND 2 MAX1921 5 PGND

65 4

MAX1920

SHDN 3

4 OUT (FB)

•1

2

3

SOT23-6

( ) ARE FOR MAX1920 ONLY

TDFN

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

19-2296; Rev 3; 8/05

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