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LTC1559-3.3/LTC1559-5

Backup Battery Controller

with Fixed Output

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Complete Battery Backup System in an SO-8,

16-Pin GN or SO Package

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Generates Fixed Backup Voltage (3.07V/4.63V) from

a Single 1.2V NiCd Button Cell

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Automatic Main Supply to Backup Switching

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Minimum 100mW Output Power

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Automatic Fast Recharge of NiCd Battery

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Programmable NiCd Trickle Charge Current

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Smart NiCd Charger Minimizes Recharge Time and

Maximizes System Efficiency After Backup

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Onboard Power-Up and Push-Button Reset

Generator

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Short-Circuit Protection

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Thermal Limiting

FEATURES

The LTC

all the functions necessary to implement a backup 3.3V or

5V power supply using a single NiCd cell. It includes a 1.2V

to 3.07V/4.63V boost converter, an intelligent 2-stage

battery charger, automatic backup switching and a micro-

processor reset generator. The boost converter uses a

synchronous switching architecture to achieve a typical

efficiency of 70%, ensuring maximum backup lifetime

from a small NiCd cell.

The on-chip NiCd charger uses an internal gas gauge to

minimize fast recharge time and prevent overcharging of

the backup cell, thereby improving system efficiency and

extending the life of the backup cell. The LTC1559 also

provides a user programmable trickle charge current to

compensate for self-discharge losses in the backup cell.

The LTC1559’s automatic backup switching scheme

requires minimum intervention from the host system and

provides feedback to the host to minimize system loading

generator eliminate the need for a separate microproces-

sor supervisory chip in most applications.

The LTC1559 is available in an SO-8, 16-pin GN or SO

package.

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Notebook Computers

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Palmtop Computers/PDAs

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Portable Instruments

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Battery-Powered Systems

, LTC and LT are registered trademarks of Linear Technology Corporation.

CTL

C1

1

µF

**BACKUP

BATTERY

1.2V

NiCd

MAIN

BATTERY

4.5V TO 28V

R1

68k

SW

LTC1559-3.3

*L1

22

µH

GND

PS

7

1

8

5

6

3

S1

RESET

1559 TA01

2

4

RESET

BACKUP

+

C3

100

µF

10V

3.3V AT NORMAL MODE

3A

33mA (3.07V) AT BACKUP MODE

>33mA (3.3V) AT NORMAL MODE

C2

1

µF

SYSTEM

µP

R2

100k

Q1

P-MOSFET

Si9424DY

* SUMIDA CD54-22

µH

** PANASONIC P-11AAH

† CONSULT LTC1435 DATA SHEET FOR

APPLICATION CIRCUIT INFORMATION

SYNCHRONOUS

BUCK

REGULATOR

+

+

Backup Time vs

0

800

700

600

500

400

300

200

100

0

15

25

1559 TA02

510

20

30

35

NiCd CELL = P-11AAH

(110mA Hrs)