Digitally Adjustable LCD Bias Supply

_______________General Description

The MAX749 generates negative LCD-bias contrast

voltages from 2V to 6V inputs. Full-scale output voltage

can be scaled to -100V or greater, and is digitally

adjustable in 64 equal steps by an internal digital-to-

analog converter (DAC). Only seven small surface-

mount components are required to build a complete

supply. The output voltage can also be adjusted using

a PWM signal or a potentiometer.

A unique current-limited control scheme reduces supply

current and maximizes efficiency, while a high switching

frequency (up to 500kHz) minimizes the size of external

components. Quiescent current is only 60µA max and is

reduced to under 15µA in shutdown mode. While shut

down, the MAX749 retains the voltage set point, simpli-

fying software control. The MAX749 drives either an

external P-channel MOSFET or a PNP transistor.

________________________Applications

Notebook Computers

Laptop Computers

Palmtop Computers

Personal Digital Assistants

Communicating Computers

Portable Data-Collection Terminals

____________________________Features

o +2.0V to +6.0V Input Voltage Range

o Flexible Control of Output Voltage:

Digital Control

Potentiometer Adjustment

PWM Control

o Output Voltage Range Set by One Resistor

o Low, 60µA Max Quiescent Current

o 15µA Max Shutdown Mode

o Small Size – 8-Pin SO and Plastic DIP Packages

_______________________________________________________________

Maxim Integrated Products

1

1

2

3

4

8

7

6

5

CS

DHI

DLOW

GND

FB

CTRL

ADJ

V+

DIP/SO

TOP VIEW

MAX749

__________________Pin Configuration

V+

ADJ

CTRL

FB

CS

DHI

DLOW

GND

ON/OFF

DIGITAL

ADJUST

1

0.1

µF

2

3

4

5

6

7

8

MAX749

__________Typical Operating Circuit

Call toll free 1-800-998-8800 for free samples or literature.

19-0143; Rev 1; 2/95

PART

TEMP. RANGE

PIN-PACKAGE

MAX749CPA

0°C to +70°C

8 Plastic DIP

MAX749CSA

0°C to +70°C

8 SO

MAX749EPA

-40°C to +85°C

8 Plastic DIP

MAX749ESA

-40°C to +85°C

8 SO

MAX749C/D

0°C to +70°C

Dice*

______________Ordering Information

* Contact factory for dice specifications.

EVALUATION

KIT MANUAL

FOLLOWS

DATA

SHEET