REV. 0

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

a

Micropower DC-DC Converter

Adjustable and Fixed 3.3 V, 5 V, 12 V

ADP1108

FUNCTIONAL BLOCK DIAGRAMS

SET

GAIN BLOCK/

ERROR AMP

COMPARATOR

SW2

FB

GND

SW1

AO

OSCILLATOR

DRIVER

A1

A2

1.245V

REFERENCE

ADP1108

SET

GAIN BLOCK/

ERROR AMP

COMPARATOR

SW2

SENSE

GND

SW1

AO

OSCILLATOR

DRIVER

A1

A2

1.245V

REFERENCE

ADP1108-3.3

ADP1108-5

ADP1108-12

R2

753k

Ω

R1

ADP1108-3.3: R1 = 456k

Ω

ADP1108-5: R1 = 250k

Ω

ADP1108-12: R1 = 87.4k

Ω

GENERAL DESCRIPTION

The ADP1108 is a highly versatile micropower switch-mode

dc-dc converter that operates from an input voltage supply as

low as 2.0 V and typically starts up from 1.8 V.

The ADP1108 can be programmed into a step-up or step-down

dc-to-dc converter with only three external components. The

fixed outputs are 3.3 V, 5 V and 12 V. An adjustable version is

also available. In step-up mode, supply voltage range is 2.0 V to

12 V, and 30 V in step-down mode. The ADP1108 can deliver

150 mA at 5 V from a 2 AA cell input and 300 mA at 5 V from

a 9 V input in step-down mode. Switch current limit can be

programmed with a single resistor.

For battery operated and power conscious applications, the

ADP1108 offers a very low power consumption of less than

110

µA.

The auxiliary gain block available in ADP1108 can be used

as a low battery detector, linear post regulator, under voltage

lockout circuit or error amplifier.

FEATURES

Operates at Supply Voltages From 2.0 V to 30 V

Consumes Only 110

A Supply Current

Step-Up or Step-Down Mode Operation

Minimum External Components Required

Low Battery Detector Comparator On-Chip

User-Adjustable Current Limit

Internal 1 A Power Switch

Fixed or Adjustable Output Voltage Versions

8-Pin DIP or SO-8 Package

APPLICATIONS

Notebook/Palm Top Computers

3 V to 5 V, 5 V to 12 V Converters

9 V to 5 V, 12 V to 5 V Converters

LCD Bias Generators

Peripherals and Add-On Cards

Battery Backup Supplies

Cellular Telephones

Portable Instruments

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106,

U.S.A.

Tel: 617/329-4700

World Wide Web Site: http://www.analog.com

Fax: 617/326-8703

© Analog Devices, Inc., 1997