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General Description

The MAX685 DC-DC converter provides low-noise dual

outputs for powering CCD imaging devices and LCDs.

This device uses a single inductor to provide indepen-

dently regulated positive and negative outputs.

Integrated power switches are included in the small

16-pin QSOP package (same size as an 8-pin SO) to

save space and reduce cost.

Each output delivers up to 10mA from a +2.7V to +5.5V

input voltage range. Output voltages are set indepen-

dently up to 24V and down to -9V. With a few additional

low-cost components, the output voltages can be set at

up to 45V and down to -16V. Output ripple magnitude is

30mVp-p. The MAX685 uses a fixed-frequency, pulse-

width-modulated (PWM) control scheme at 220kHz or

400kHz to permit output noise filtering and to reduce

the size of external components. The frequency can

also be synchronized to an external clock signal

between 200kHz and 480kHz.

The MAX685 has a power-OK indicator output (POK)

that signals when both outputs are within regulation. A

logic-controlled shutdown completely turns off both out-

puts and reduces supply current to 0.1µA. The user

can also set which output turns on first.

The preassembled MAX685 evaluation kit is available to

reduce design time.

Applications

Camcorders

LCDs

Digital Cameras

CCD Imaging Devices

Notebooks

Features

o Dual Output Using a Single Inductor

o Low-Noise Output, 30mVp-p Ripple

o Output Voltages up to 24V and down to -9V

(up to 45V and down to -16V with added

components)

o Internal Switches in a Small Package

o 220kHz/400kHz Fixed-Frequency PWM Operation

o Frequency Can Be Synchronized to

External Clock

o Power-OK Indicator

o Selectable Power-On Sequencing

o 0.1µA Logic-Controlled Shutdown

Dual-Output (Positive and Negative),

DC-DC Converter for CCD and LCD

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Maxim Integrated Products

1

MAX685

VP

ON

OFF

INPUT

2.7V TO 5.5V

LXN

FBP

LXP

FBN

REF

GND

NEGATIVE

OUTPUT

DOWN TO -9V,

10mA

POSITIVE

OUTPUT

UP TO 24V,

10mA

SHDN

SYNC

SEQ

POK

POS

NEG

OPTIONAL

POWER-OK

INDICATOR

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

LXP

LXN

I.C.

PGND

PGND

FBP

REF

FBN

GND

TOP VIEW

MAX685

QSOP

I.C.

I.C. = INTERNALLY CONNECTED

VP

SHDN

POK

SEQ

SYNC

Typical Operating Circuit

19-1353; Rev 0; 4/98

PART

MAX685EEE

-40°C to +85°C

TEMP. RANGE

PIN-PACKAGE

16 QSOP

EVALUATION

KIT

AVAILABLE

Pin Configuration

Ordering Information