General Description

The MAX1556/MAX1556A/MAX1557 are low-operating-

current (16µA), fixed-frequency step-down regulators.

High efficiency, low-quiescent operating current, low

dropout, and minimal (27µA) quiescent current in

dropout make these converters ideal for powering

portable devices from 1-cell Li-ion or 3-cell alkaline/NiMH

batteries. The MAX1556 delivers up to 1.2A; has pin-

selectable 1.8V, 2.5V, and 3.3V outputs; and is also

adjustable. The MAX1557 delivers up to 600mA; has pin-

selectable 1V, 1.3V, and 1.5V outputs; and is also

adjustable.

The MAX1556/MAX1556A/MAX1557 contain a low-on-

resistance internal MOSFET switch and synchronous

rectifier to maximize efficiency and dropout perfor-

mance while minimizing external component count. A

proprietary topology offers the benefits of a high fixed-

frequency operation while still providing excellent effi-

ciency at both light and full loads. A 1MHz PWM

switching frequency keeps components small. Both

devices also feature an adjustable soft-start to minimize

battery transient loading.

The MAX1556/MAX1556A/MAX1557 are available in a

tiny 10-pin TDFN (3mm x 3mm) package.

Applications

PDAs and Palmtop Computers

Cell Phones and Smart Phones

Digital Cameras and Camcorders

Portable MP3 and DVD Players

Hand-Held Instruments

Features

o Up to 97% Efficiency

o 95% Efficiency at 1mA Load Current

o Low 16µA Quiescent Current

o 1MHz PWM Switching

o Tiny 3.3µH Inductor

o Selectable 3.3V, 2.5V, 1.8V, 1.5V, 1.3V, 1.2V, 1.0V,

and Adjustable Output

o 1.2A Guaranteed Output Current

(MAX1556/MAX1556A)

o Voltage Positioning Optimizes Load-Transient

Response

o Low 27µA Quiescent Current in Dropout

o Low 0.1µA Shutdown Current

o No External Schottky Diode Required

o Analog Soft-Start with Zero Overshoot Current

o Small, 10-Pin, 3mm x 3mm TDFN Package

Step-Down DC-DC Converters

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Maxim Integrated Products

1

TOP VIEW

LX

OUT

SHDN

6

7

8

9

10

INP

D1

3

2

1

SS

GND

IN

5

PGND

D2

4

TDFN

MAX1556

MAX1556A

MAX1557

Pin Configuration

Ordering Information

LX

SS

ON

OFF

SHDN

GND

INPUT

2.6V TO 5.5V

VOLTAGE

SELECT

OUTPUT

PGND

OUT

INP

IN

D1

D2

MAX1556

MAX1556A

MAX1557

Typical Operating Circuit

19-3336; Rev 2; 6/10

EVALUATION

KIT

AVAILABLE

PART

TEMP RANGE

PIN-PACKAGE

TOP

MARK

MAX1556ETB+

-40

°C to +85°C 10 TDFN-EP*

ACQ

MAX1556AETB+

-40

°C to +85°C 10 TDFN-EP*

AUJ

MAX1557ETB+

-40

°C to +85°C 10 TDFN-EP*

ACR

*

EP = Exposed paddle.

+

Denotes a lead(Pb)-free/RoHS-compliant package.

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.