General Description

The MAX1920/MAX1921 step-down converters deliver

over 400mA to outputs as low as 1.25V. These convert-

ers 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 combi-

nation makes the MAX1920/MAX1921 excellent high-

efficiency alternatives 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.

Applications

Next-Generation Wireless Handsets

PDAs, Palmtops, and Handy-Terminals

Battery-Powered Equipment

CDMA Power Amplifier Supply

Features

o 400mA Guaranteed Output Current

o Internal Synchronous Rectifier for >90%

Efficiency

o Tiny 6-Pin SOT23 Package

o Up to 1.2MHz Switching Frequency for Small

External Components

o 50µA Quiescent Supply Current

o 0.1µA Logic-Controlled Shutdown

o 2V to 5.5V Input Range

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

Voltages (MAX1921)

o Adjustable Output Voltage (MAX1920)

o ±1.5% Initial Accuracy

o Soft-Start Limits Startup Current

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.

Low-Voltage, 400mA Step-Down

DC-DC Converters in SOT23

________________________________________________________________ Maxim Integrated Products

1

19-2296; Rev 1; 7/02

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

MAX1921

IN

AGND

SHDN

LX

PGND

OUT

OFF

ON

4.75k

Ω

4.7

µF

4.7

µH

5600pF

OUTPUT

1.5V UP TO 400mA

INPUT

2V TO 5.5V

Typical Operating Circuit

PART

TEMP RANGE

PIN-PACKAGE

MAX1920EUT-T

-40°C to +85°C

6 SOT23-6

MAX1921EUT_ _-T

-40°C to +85°C

6 SOT23-6

Ordering Information

AGND

OUT (FB)

SHDN

16

LX

5

PGND

IN

MAX1920

MAX1921

SOT23-6

TOP VIEW

2

34

( ) ARE FOR MAX1920 ONLY

Pin Configuration