_______________Detailed Description

The MAX1612/MAX1613 manage the bridge battery

(auxiliary battery) in portable systems. These devices

consist of a timer block that monitors the charging

process, a linear regulator for supplying IC power and

external circuitry to the MAX1612/MAX1613, and a DC-

DC step-up converter that powers the system when the

main battery is removed (Figure 1). The boost DC-DC

converter reduces the number of bridge-battery cells

required to supply the system’s DC-DC converter.

When the main supply is present, the DC-DC converter

is inactive, reducing the drain on the main battery to

only 18µA. However, if the main battery voltage falls (as

detected by the low-battery comparator), the bridge

battery becomes the input source.

The MAX1612/MAX1613 have an internal linear regula-

tor set at +5V (MAX1612) or +3.3V (MAX1613). The lin-

ear regulator can deliver a load up to 10mA, making it

capable of powering external components such as a

microcontroller (Figure 4). An undervoltage lockout fea-

ture disables the device when the input voltage falls

below the operating range, preventing the DC-DC con-

verter from inadvertently powering up.

The MAX1612/MAX1613 feature an internal counter

intended to track the charging and discharging

process. The counter tracks the charge on the bridge

battery, allowing trickle charge to terminate when the

maximum charge is achieved. The charging rate is

determined by current through the ISET switch, and

limited by the switch’s maximum current specification

as well as by the bridge cell’s charging capability. As

Bridge-Battery Backup Controllers

for Notebooks

6

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N-CHANNEL

PGND

L1

ISET

LRI

BBATT

LX

FB

D1

R1

R2

R3

LBI

DISCHARGE

OSCILLATOR

TIMER BLOCK

CHARGE/DISCHARGE

COUNTER

CHARGE

OSCILLATOR

2.0V

REFERENCE

+3.3/+5V

LINEAR REGULATOR

1.8V/2.0V

BBON

DCMD

CCMD

FULL

CD

CC

GND

LRO

TO EXTERNAL

LOADS

LBO

TO MAIN

DC-DC

MAX1612

MAX1613

PULSE-

FREQUENCY

MODULATION

CONTROL

BLOCK

Figure 1. Functional Diagram