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-toanalog converter (DAC). Only seven small surfacemount 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, simplifying software control. The MAX749 drives either an external P-channel MOSFET or a PNP transistor

Features

♦ +2.0V to +6.0V Input Voltage Range

♦ Flexible Control of Output Voltage: Digital Control Potentiometer Adjustment PWM Control

♦ Output Voltage Range Set by One Resistor

♦ Low, 60µA Max Quiescent Current

♦ 15µA Max Shutdown Mode

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

Applications

Notebook Computers Laptop Computers Palmtop Computers

Personal Digital Assistants Communicating Computers Portable Data-Collection Terminals

Typical Operating Characteristics