_______________General Description

The MAX768 low-noise, dual-output, regulated charge

pump provides a negative output for biasing GaAsFET

power amplifiers, and a positive output for powering

voltage-controlled oscillators (VCOs) in wireless hand-

sets. The outputs can also be used to power LCDs.

Output ripple is less than 2mVp-p. The MAX768 is

intended for use in low-voltage systems where a simple

charge-pump inverter is inadequate, or where the VCO

needs more range to improve its signal-to-noise ratio.

The input range is 2.5V to 5.5V, enabling direct power

from 1Li+ and 3-cell NiMH/NiCd batteries.

The MAX768 includes a voltage-doubler charge pump,

followed by an inverting charge pump. This combina-

tion produces unregulated outputs that are ±2x the

input. Two internal low-dropout linear regulators provide

the low-noise, regulated positive and negative outputs.

Output current is guaranteed to be at least 5mA per

output. The linear regulators use CMOS devices, so the

quiescent current remains independent of output load-

ing (even in dropout), and the dropout voltage

approaches zero with no load current.

The MAX768 has two preset switching frequencies

(25kHz or 100kHz), or can be synchronized by an exter-

nal clock from 20kHz to 240kHz. This flexibility permits

users to optimize their designs based on noise, capaci-

tor size, and quiescent-supply-current criteria.

The device features Dual Mode™ operation: the output

voltage is preset to +5V and -5V, or can be adjusted by

adding external resistor dividers. Other features include

independent shutdowns and a logic output that signals

when the negative voltage has risen to within 10% of its

regulation setpoint (to protect the power amplifier

GaAsFET). The MAX768 is available in a space-saving,

16-pin QSOP, which is the same size as a standard

8-pin SO.

________________________Applications

GaAsFET Power Amp Bias

Voltage-Controlled Oscillator (VCO) Supply

Tuner Diode Power Supply

Positive and Negative LCD Supply

Cellular Phone

PCS and Cordless Phone

Wireless Handsets

Wireless Handheld Computers

Wireless PCMCIA Cards

Modems

____________________________Features

o Dual Positive/Negative Regulated Outputs:

o Output-Ready Indicator to Protect GaAsFET PAs

o 2.5V to 5.5V Input Voltage Range

o Low-Noise Output Ripple: < 2mVp-p

o Synchronizable Switching Frequency

o Uses Only Small, Low-Cost Capacitors

o 0.1µA Independent Shutdown Controls

o Adjustable Output Voltages

o Small 16-Pin QSOP Package

Low-Noise, Dual-Output, Regulated Charge Pump

for GaAsFET, LCD, and VCO Supplies

________________________________________________________________

Maxim Integrated Products

1

MAX768

POUT

V+

C3

C5

C7

POSITIVE

OUTPUT

+5V

NEGATIVE

OUTPUT

-5V

OUTPUT-

READY

SIGNAL

C6

C4

C1

C2

V-

NOUT

RDY

SYNC

(3.0V TO 5.5V)

IN

GND

SETP

SETN

PSHDN

NSHDN

C1+

C1-

C2+

C2-

__________Typical Operating Circuit

19-1174; Rev 0; 12/96

PART

MAX768C/D

MAX768EEE

-40°C to +85°C

0°C to +70°C

TEMP. RANGE

PIN-PACKAGE

Dice*

16 QSOP

______________Ordering Information

*

Pin Configuration appears at end of data sheet.

Dual Mode is a trademark of Maxim Integrated Products.

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800