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General Description

The MAX848/MAX849 boost converters set a new stan-

dard of high efficiency and high integration for noise-

sensitive power-supply applications, such as portable

phones and small systems with RF data links. The heart

of the these devices is a synchronous boost-topology

regulator that generates a fixed 3.3V output (or 2.7V to

5.5V adjustable output) from one to three NiCd/NiMH

cells or one Li-Ion cell.

Synchronous rectification provides a 5% efficiency

improvement over similar nonsynchronous boost regu-

lators. In standby mode, pulse-skipping PFM operation

keeps the output voltage alive with only 150µW quies-

cent power consumption. Fixed-frequency PWM opera-

tion ensures that the switching noise spectrum is limited

to the 300kHz fundamental and its harmonics, allowing

easy post-filtering noise reduction. For even tighter

noise spectrum control, synchronize to a 200kHz to

400kHz external clock.

Battery monitoring is provided by a two-channel, volt-

age-to-frequency analog-to-digital converter (ADC).

One channel is intended for a single-cell battery input

(0.625V to 1.875V range), while the other channel is for

monitoring higher voltages (0V to 2.5V range).

Two control inputs are provided for push-on, push-off

control via a momentary pushbutton switch. Upon

power-up, an internal comparator monitors the output

voltage to generate a power-good output (POK).

The devices differ only in the current limit of the

N-channel MOSFET power switch: 0.8A for the

MAX848, and 1.4A for the MAX849.

Features

o Up to 95% Efficiency

(see

Typical Output Selector Guide below)

o 3.3V Dual Mode™ or 2.7V to 5.5V Adj. Output

o 0.7V to 5.5V Input Range

o 0.15mW Standby Mode

o 300kHz PWM Mode or Synchronizable

o Two-Channel ADC with Serial Output

o Power-Good Function

Applications

Digital Cordless Phones

PCS Phones

Cellular Phones

Hand-Held Instruments

Palmtop Computers

Personal Communicators

Local 3.3V to 5V Supplies

1-Cell to 3-Cell, High-Power,

Low-Noise, Step-Up DC-DC Converters

________________________________________________________________

Maxim Integrated Products

1

AIN1

AIN2

AINSEL

DATA

ON1

ON2

CLK/SEL

POKIN

LX

OUT

POUT

POK

FB

MAX848

MAX849

OUTPUT

A/D CHANNEL 1 IN

A/D CHANNEL 2 IN

A/D CHANNEL SELECT

A/D OUTPUT

ON/OFF CONTROL

SYNC INPUT

INPUT

0.8V TO 5.5V

VOLTAGE MONITOR

OUTPUT

REF

GND

PGND

Typical Operating Circuit

19-1095; Rev 2; 12/97

PART

MAX848ESE

MAX849ESE

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE

PIN-PACKAGE

16 Narrow SO

16 Narrow SO

Ordering Information

Pin Configuration appears at end of data sheet.

Dual Mode is a trademark of Maxim Integrated Products.

Typical Output Selector Guide

(V)

(V)

(mA)

(mA)

0.9

3.3

100

70

5

70

40

1.2

3.3

300

110

5

200

70

2.4

3.3

750

200

5

500

130

2.7

3.3

800

250

5

600

150

3.6

5

1000

300