General Description

The MAX1955/MAX1956 are dual-output, fixed-frequency,

voltage-mode, pulse-width modulated (PWM) step-down

controllers with 0.5% output accuracy. Each controller

switches at a constant 600kHz and is 180° out-of-phase

with the other controller, reducing input ripple current

and the number of input capacitors.

An on-chip bias supply generates a 5V gate drive to

deliver up to 25A output current per phase with low-cost

N-channel MOSFETs at up to 93% efficiency. Lossless

adjustable current limit eliminates expensive current-

sense resistors and improves efficiency. Foldback current

limit reduces power dissipation during short-circuit

conditions and handles transient overloads better than

controllers using hiccup-mode short-circuit protection.

Output voltage margining shifts output voltage by

±4% from the nominal value to simplify system test.

Outputs also can be powered up and down in select-

able sequences to meet core and logic supply-rail

requirements.

The MAX1955/MAX1956 are available in a 28-lead thin

QFN package with exposed pad.

Applications

Base Stations

Telecom and Network Equipment

Servers

DSP, ASIC, µP, and FPGA Supplies

Features

o Operates from a 1.6V to 5.5V Supply (MAX1956)

o 0.5% Output Accuracy

o Up to 25A per Phase Output Current

o On-Chip Boost Regulator Provides 5V Gate Drive

o Up to 93% Efficiency

o 180° Out-of-Phase Operation

o ±4% Voltage Margining

o Lossless, Foldback Current Limit

o Selectable Voltage Sequencing

o Synchronizable to External Clock

o Digital Soft-Start and Soft-Stop

1.6V to 5.5V Input, 0.5% Accurate, Dual

180° Out-of-Phase Step-Down Controllers

________________________________________________________________ Maxim Integrated Products

1

Ordering Information

LXB

BST1

DH1

LX1

DL1

PGND

FB1

COMP1

SEQ

SYNC

SYNCHRONIZATION

CLOCK

EN

ON/OFF

VOLTAGE

MARGINING

BST2

DH2

LX2

DL2

FB2

COMP2

REF

GND

ILIM1

ILIM2

IN

INPUT

1.6V TO 5.5V

OUTPUT 1

UP TO 25A

OUTPUT 2

UP TO 25A

VDD

VDD

MAX1956

Typical Operating Circuit

19-2623; Rev 0; 1/03

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.

EVALUATION

KIT

AVAILABLE

PART

TEMP RANGE

PIN-PACKAGE

MAX1955ETI

-40

°C to +85°C

28 Thin QFN-EP*

MAX1956ETI

-40

°C to +85°C

28 Thin QFN-EP*

Pin Configuration appears at end of data sheet.