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General Description

The MAX8743 is a dual pulse-width modulation (PWM)

controller configured for step-down (buck) topologies

that provides the high efficiency, excellent transient

response, and high DC output accuracy necessary for

stepping down high-voltage batteries to generate low-

voltage chipset and RAM power supplies in notebook

computers. The CS_ inputs can be used with low-side

sense resistors to provide accurate current limits or can

be connected to LX_, using low-side MOSFETs as cur-

rent-sense elements. High output impedance in shut-

down eliminates negative output voltages, saving the

cost of a Schottky diode at the output.

The on-demand PWM controllers are free running, con-

stant on-time with input feed-forward. This configuration

provides ultra-fast transient response, wide input-output

differential range, low supply current, and tight load-reg-

ulation characteristics. The MAX8743 is simple and easy

to compensate.

Single-stage buck conversion allows the MAX8743 to

directly step down high-voltage batteries for the highest

possible efficiency. Alternatively, two-stage conversion

(stepping down the 5V system supply instead of the bat-

tery at a higher switching frequency) allows the minimum

possible physical size.

The MAX8743 is intended for generating chipset, DRAM,

CPU I/O, or other low-voltage supplies down to 1V. The

MAX8743 is available in 28-pin QSOP and 36-pin thin

QFN packages.

Applications

Notebook Computers

CPU Core Supplies

Chipset/RAM Supplies as Low as 1V

1.8V and 2.5V I/O Supplies

Features

♦ Ultra-High Efficiency

♦ Accurate Current-Limit Option

♦ Quick-PWM™ with 100ns Load-Step Response

♦ High Output Impedance in Shutdown

♦ Dual Mode™ Fixed 1.8V/1.5V/Adj or 2.5V/Adj Outputs

♦ Adjustable 1V to 5.5V Output Range

♦ 2V to 28V Battery Input Range

♦ 200kHz/300kHz/420kHz/540kHz Nominal Switching

Frequency

♦ Adjustable Overvoltage Protection

♦ 1.7ms Digital Soft-Start

♦ Drives Large Synchronous-Rectifier FETs

♦ Power-Good Window Comparator

♦ 2V ±1% Reference Output

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

________________________________________________________________ Maxim Integrated Products

1

19-3318; Rev 0; 6/04

Pin Configurations appear at end of data sheet.

Quick-PWM and Dual Mode are trademarks of Maxim Integrated

Products, Inc.

OUTPUT1

1.8V

BATTERY

4.5V TO 28V

ILIM1

ON2

DL1

TON

OUT1

LX1

DH1

FB1

GND

BST1

ILIM2

ON1

REF

DL2

CS2

OUT2

LX2

DH2

FB2

V+

BST2

SKIP

5V INPUT

PGOOD

OUTPUT2

2.5V

MAX8743EEI

UVP

OVP

CS1

Minimal Operating Circuit

Ordering Information

PART

TEMP RANGE

PIN-PACKAGE

MAX8743EEI

-40°C to +85°C

28 QSOP

MAX8743ETX

-40°C to +85°C

36 Thin QFN

6mm x 6mm