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.

General Description

The MAX1845 is a dual PWM controller configured for

step-down (buck) topologies that provides high efficien-

cy, excellent transient response, and high DC output

accuracy necessary for stepping down high-voltage bat-

teries 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 current-sense elements.

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 MAX1845 is simple and easy

to compensate.

Single-stage buck conversion allows the MAX1845 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 MAX1845 is intended for generating chipset, DRAM,

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

single-output version, refer to the MAX1844 data sheet.

The MAX1845 is available in 28-pin QSOP and 36-pin

thin QFN packages.

Applications

Notebook Computers

CPU Core Supplies

Chipset/RAM Supply as Low as 1V

1.8V and 2.5V I/O Supplies

Features

o Ultra-High Efficiency

o Accurate Current-Limit Option

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

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

o Adjustable 1V to 5.5V Output Range

o 2V to 28V Battery Input Range

o 200/300/420/540kHz Nominal Switching Frequency

o Adjustable Overvoltage Protection

o 1.7ms Digital Soft-Start

o Drives Large Synchronous-Rectifier FETs

o Power-Good Window Comparator

o 2V ±1% Reference Output

Dual, High-Efficiency, Step-Down

Controller with Accurate Current Limit

________________________________________________________________ Maxim Integrated Products

1

19-1955; Rev 2; 1/03

Pin Configurations appear at end of data sheet.

Quick-PWM and Dual Mode are trademarks of Maxim Integrated

Products.

EVALUATION

KIT

AVAILABLE

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

MAX1845EEI

UVP

OVP

CS1

Minimal Operating Circuit

Ordering Information

PART

TEMP RANGE

PIN-PACKAGE

MAX1845EEI

-40°C to +85°C

28 QSOP

MAX1845ETX

-40°C to +85°C

36 Thin QFN