General Description

The MAX1809 is a reversible energy flow, constant-off-

time, pulse-width modulated (PWM), step-down DC-DC

converter. It is ideal for use in notebook and subnote-

book computers that require 1.1V to 5V active

termination power supplies. This device features an

internal PMOS power switch and internal synchronous

rectifier for high efficiency and reduced component

count. The internal 90m

Ω PMOS power switch and

70m

Ω NMOS synchronous-rectifier switch easily deliver

continuous load currents up to 3A. The MAX1809 accu-

rately tracks an external reference voltage, produces

efficiencies as high as 93%.

The MAX1809 uses a unique current-mode, constant-

off-time, PWM control scheme that allows the output to

source or sink current. This feature allows energy to

return to the input power supply that otherwise would

be wasted. The programmable constant-off-time archi-

tecture sets switching frequencies up to 1MHz, allowing

the user to optimize performance trade-offs between

efficiency, output switching noise, component size, and

cost. The MAX1809 features an adjustable soft-start to

limit surge currents during startup, a 100% duty-cycle

mode for low-dropout operation, and a low-power shut-

down mode that disables the power switches and

reduces supply current below 1µA. The MAX1809 is

available in a 28-pin QFN with an exposed backside

pad, a 28-pin thin QFN, or a 16-pin QSOP.

Applications

DDR Memory Termination

Active Termination Buses

Features

o Source/Sink 3A

o ±1% Output Accuracy

o Up to 1MHz Switching Frequency

o 93% Efficiency

o Internal PMOS/NMOS Switches

90m

110m

o 3V to 5.5V Input Voltage Range

o <1µA Shutdown Supply Current

o Programmable Constant-Off-Time Operation

o Thermal Shutdown

o Adjustable Soft-Start Inrush Current Limiting

o Output Short-Circuit Protection

3A, 1MHz, DDR Memory Termination Supply

________________________________________________________________ Maxim Integrated Products

1

IN

N.C.

LX

IN

N.C.

SS

EXTREF

PGND

PGND

LX

LX

PGND

GND

TOP VIEW

THIN QFN

15

16

17

18

19

20

21

7

6

5

4

3

2

1

MAX1809

Pin Configurations

Ordering Information

MAX1809

IN

SHDN

EXTREF

TOFF

LX

PGND

GND

FB

REF

SS

Typical Operating Circuit

19-2142; Rev 1; 9/02

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.

PART

TEMP RANGE

PIN-PACKAGE

MAX1809EGI*

-40°C to +85°C

28 QFN

MAX1809EEE

-40°C to +85°C

16 QSOP

MAX1809ETI

-40°C to +85°C

28 Thin QFN

Pin Configurations continued at end of data sheet.

*Contact factory for availability.