General Description

The MAX1677 is a compact, high-efficiency, dual-out-

put boost converter for portable devices needing two

regulated supplies, typically for logic and liquid crystal

displays (LCDs). Operation with inputs as low as 0.7V

allows the MAX1677 to accept 1, 2, or 3-cell alkaline,

NiCd, or NiMH batteries as well as 1-cell lithium-ion bat-

teries. The device requires no external FETs and can

maintain regulation while consuming only 20µA, making

it ideal for hand-held pen-input and PDA devices oper-

ating with low-current “sleep” states.

The MAX1677’s primary regulator supplies up to

350mA at either a factory-preset 3.3V or an adjustable

2.5V to 5.5V output. On-chip synchronous rectification

provides efficiencies up to 95%. 300kHz (or externally

clocked) pulse-width-modulation (PWM) operation is

particularly suitable for applications needing low noise,

such as those with wireless features. The primary con-

verter also features pin-selectable pulse-frequency-

modulation (PFM) operation that consumes only 20µA.

A 1µA shutdown state also minimizes battery drain.

The MAX1677’s secondary step-up converter supplies up

to +28V or -28V for LCD bias, varactor tuning, or other

high-voltage, low-current functions. Other MAX1677 fea-

tures include precision reference, logic control inputs for

both regulators, and an uncommitted comparator for

low-battery detection or a reset function. The MAX1677

is supplied in Maxim’s compact 16-pin QSOP package,

which occupies no more space than a standard SO-8.

Applications

PDAs

Portable Phones

Hand-Held Terminals

Portable Instruments

Features

o No External FETs Required

o Main Output

Up to 350mA for Logic Supply

Fixed 3.3V or Adjustable (2.5V to 5.5V)

Synchronous Rectification for High Efficiency

(up to 95%)

300kHz (200kHz to 400kHz Synchronizable)

Fixed-Frequency PWM Operation

o Secondary Output

Up to +28V or -28V for LCD Bias

Programmable Current Limit

o 0.7V to 5.5V Input Voltage Range

o 20µA Quiescent Current

o 1µA Shutdown Current

o Low-Battery Comparator

o Small 16-Pin QSOP Package

Compact, High-Efficiency, Dual-Output

Step-Up and LCD Bias DC-DC Converter

________________________________________________________________ Maxim Integrated Products

1

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

OUT

POUT

LX

PGND

LCDGND

LCDLX

ON

LCDFB

GND

TOP VIEW

MAX1677

FB

LBI

LCDON

LBO

CLK/SEL

LCDPOL

REF

QSOP

19-1403; Rev 1; 3/01

PART

MAX1677EEE

-40°C to +85°C

TEMP RANGE

PIN-PACKAGE

16 QSOP

EVALUATION

KIT

AVAILABLE

Pin Configuration

Ordering Information

Typical Operating Circuit

MAX1677

LX

POUT

OUT

±28V

LCD

BOOST

OUTPUT

3.3V MAIN

BOOST OUTPUT

LCDFB

REF

FB

LCDGND

GND

LCDLX

LCDON

LBI

ON

OFF

LBO

CLK/SEL

ON

LCDPOL

PGND

PWM

PFM

ON

OFF

+VE OUT

-VE OUT

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.