General Description

The MAX686 DAC-controlled boost/inverter IC converts

a positive input voltage to a positive or negative LCD

bias voltage up to +27.5V or -27.5V. The device features

an internal N-channel MOSFET switch, programmable

current limiting, and an internal 6-bit digital-to-

analog converter (DAC) for digital adjustment of the

output voltage. It comes in a small 16-pin QSOP pack-

age (same size as an 8-pin SO).

The MAX686 uses a current-limited, pulse-frequency-

modulation (PFM) control scheme to provide high effi-

ciency over a wide range of load conditions. Its high

switching frequency (up to 300kHz) allows the use of

small external components.

An LCDON output allows the LCD bias voltage to be

automatically disabled when the display logic voltage is

removed, protecting the display. The MAX686 has a

+2.7V to +5.5V input voltage range for the IC, and a

+0.8V to +27.5V input voltage range for the inductor.

Typical quiescent supply current is 65µA. Shutdown

current is 1.5µA.

The MAX686 offers high-level integration to save space,

reduce power consumption, and increase battery life,

making it an excellent choice for battery-powered

portable equipment. The MAX629 is similar to the

MAX686, except that it does not contain a built-in DAC.

Both devices have evaluation kits to facilitate designs.

Applications

Positive or Negative LCD Bias

Personal Digital Assistants

Notebook Computers

Portable Data-Collection Terminals

Palmtop Computers

Varactor Tuning Diode Bias

____________________________Features

o Internal 500mA, 28V N-Channel Switch

(no external FET required)

o Adjustable Output Voltage to +27.5V or -27.5V

o 6-Bit DAC-Controlled Output Voltage

o Up to 90% Efficiency

o Small 16-Pin QSOP Package

(Same size as 8-pin SO)

o Power-OK Indicator

o 65µA Quiescent Current

o 1.5µA Shutdown Current

o Up to 300kHz Switching Frequency

DAC-Controlled Boost/Inverter

LCD Bias Supply with Internal Switch

________________________________________________________________

Maxim Integrated Products

1

19-1327; Rev 1; 2/98

PART

MAX686C/D

MAX686EEE

-40°C to +85°C

0°C to +70°C

TEMP. RANGE

PIN-PACKAGE

Dice*

16 QSOP

EVALUATION

KIT

AVAILABLE

Ordering Information

*

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

For small orders, phone 408-737-7600 ext. 3468.

Functional Diagram appears at end of data sheet.

MAX686

22

µH

UP

SHDN

DN

POL

GND

PGND

LX

DACOUT

LCDON

FB

REF

POK

ISET

0.1

µF

R3

R2

MBR0530L

R1

ON/OFF

DAC CONTROL

0.1

µF

Typical Operating Circuit

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

PGND

LX

N.C.

LCDON

GND

POK

FB

REF

TOP VIEW

MAX686

QSOP

UP

DN

ISET

POL

SHDN

DACOUT

Pin Configuration