General Description

The MAX1970/MAX1971/MAX1972 dual-output current-

mode PWM buck regulators operate from 2.6V to 5.5V

input and deliver a minimum of 750mA on each output.

The MAX1970 and MAX1972 operate at a fixed 1.4MHz

(MAX1971 operates at 700kHz) to reduce output induc-

tor and capacitor size and cost. Switching the regula-

tors 180° out-of-phase also reduces the input capacitor

size and cost. Ceramic capacitors can be used for

input and output.

using external feedback resistors, or can be preset to

1.8V or 3.3V for output 1 and 1.5V or 2.5V for output 2.

When one output is higher than 1.2V, the second can

be configured down to sub-1V levels. Output accuracy

is better than ±1% over variations in load, line, and tem-

perature. Internal soft-start reduces inrush current dur-

ing startup.

All devices feature power-on reset (POR). The

MAX1971 includes a reset input (RSI), which forces

POR low for 175ms after RSI goes low. The MAX1970

and MAX1972 include an open-drain power-fail output

(PFO) that monitors input voltage and goes high when

the input falls below 3.94V. For USB-powered xDSL

modems, this output can be used to detect USB power

failure. A minimum switching frequency of 1.2MHz

ensures operation outside the xDSL band.

Applications

Features

o Current-Mode, 1.4MHz Fixed-Frequency PWM

Operation

o 180° Out-of-Phase Operation Reduces Input

Capacitor

o ±1% Output Accuracy Over Load, Line, and

Temperature Ranges

o 750mA Guaranteed Output Current

o 2.6V to 5.5V Input

o Power-On Reset Delay of 16.6ms (MAX1970) or

175ms (MAX1971 and MAX1972)

o Power-Fail Output (MAX1970 and MAX1972 Only)

o Power-On Reset Input (MAX1971 Only)

o Operation Outside xDSL Band

o Ultra-Compact Design with Smallest External

Components

and 1.5V/2.5V Preset

o All-Ceramic Capacitor Application

o Soft-Start Reduces Inrush Current

Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-

Down Regulator with POR and RSI/PFO

________________________________________________________________ Maxim Integrated Products

1

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

LX1

PGND

LX2

IN

FBSEL1

FBSEL2

PF0 (MAX1970/MAX1972)

RSI (MAX1971)

EN

POR

TOP VIEW

MAX1970

MAX1971

MAX1972

QSOP

COMP1

COMP2

FB1

FB2

REF

GND

Pin Configuration

RSI

EN

COMP1

COMP2

FBSEL1

FBSEL2

REF

POR

POR

OUT1

1.8V

750mA

OUT2

2.5V

750mA

RSI

LX1

FB2

FB1

LX2

PGND

IN

MAX1971

EN

Typical Operating Circuit

19-2297; Rev 0; 1/02

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.

xDSL Modems

xDSL Routers

Copper Gigabit SFP

and GBIC Modules

USB-Powered Devices

Dual LDO Replacement

Ordering Information

PART

TEMP RANGE

PIN-PACKAGE

MAX1970EEE

-40

°C to +85°C

16 QSOP

MAX1971EEE

-40

°C to +85°C

16 QSOP

MAX1972EEE

-40

°C to +85°C

16 QSOP