_______________General Description

The MAX840/MAX843/MAX844 low-noise, inverting

charge-pump power supplies are ideal for biasing

GaAsFETs in cellular telephone transmitter amplifiers.

They operate with inputs down to 2.5V.

The MAX840 offers both a -2V preset output and a -0.5V

to -9.4V adjustable output. The MAX843/MAX844 use

an external positive control voltage to set the negative

output voltage. Input voltage range for all the devices is

These circuits can operate with small capacitors, as low

as 0.22µF.

An internal linear regulator reduces the MAX840’s out-

put voltage ripple to 1mVp-p. With a well-filtered control

than 1mVp-p typical output ripple. Supply current is

750µA, and reduces to less than 1µA in shutdown

(MAX840/MAX843). The MAX844’s unregulated output

is active in shutdown, with the charge pump switching at

20kHz. It provides a low-power LCD supply.

________________________Applications

Cellular Phones

GaAsFET Power Amplifier Modules

Personal Communicators, PDAs

Wireless Data Loggers

Continuously Adjustable GaAsFET Bias

LCD-Bias Contrast Control

Regulated Negative Power Supplies

____________________________Features

o Fixed -2V or Adjustable -0.5V to -9.4V Output

at 4mA (MAX840)

o 2.5V to 10V Input Voltage Range

o Operate with Small Capacitors (as low as 0.22µF)

o 1mVp-p Output Voltage Ripple

o Charge-Pump Switching Frequency:

100kHz in Normal Operation

20kHz in Shutdown Mode (MAX844)

o 1µA Max Logic-Level Shutdown Over Temp.

(MAX840/MAX843)

o Small 8-Pin SO Package

Low-Noise, Regulated, -2V GaAsFET Bias

________________________________________________________________

Maxim Integrated Products

1

( ) ARE FOR MAX843/MAX844

1

2

3

4

8

7

6

5

IN

GND

OUT

FB (CONT)

SHDN

NEGOUT

C1-

C1+

MAX840

MAX843

MAX844

SO

TOP VIEW

__________________Pin Configuration

MAX840

FB

OUT

SHDN

NEGOUT

C1-

C1+

IN

GND

(3 CELLS)

0.22

µF

4.7

µF

0.22

µF

0.22

µF

ON/OFF

__________Typical Operating Circuit

19-0388; Rev 1; 3/96

PART

MAX840C/D

MAX840ISA

MAX840ESA

-40°C to +85°C

-25°C to +85°C

0°C to +70°C

TEMP. RANGE

PIN-PACKAGE

Dice*

8 SO

8 SO

EVALUATION

KIT MANUAL

FOLLOWS

DATA

SHEET

______________Ordering Information

MAX843C/D

0°C to +70°C

Dice*

MAX843ISA

-25°C to +85°C

8 SO

MAX843ESA

-40°C to +85°C

8 SO

MAX844C/D

0°C to +70°C

Dice*

MAX844ISA

-25°C to +85°C

8 SO

MAX844ESA

-40°C to +85°C

8 SO

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