MAX1612 Datasheet, PDF (6/12 Pages) Maxim Integrated Products – Bridge-Battery Backup Controllers for Notebooks

Bridge-Battery Backup Controllers
for Notebooks
V_MAIN
V_CHARGE
L1
R_ISET
V_BBATT
TO MAIN
DC-DC
C_OUT
TO EXTERNAL
LOADS
LRI
LRO
+3.3/+5V
LINEAR REGULATOR
2.0V
REFERENCE
GND
D1
ISET
BBATT
MAX1612
MAX1613
LX
PULSE-
FREQUENCY
MODULATION
N-CHANNEL
PGND
R1
CONTROL
BLOCK
FB
CC
CHARGE
OSCILLATOR
C_CC
CD
DISCHARGE
OSCILLATOR
C_CD
TIMER BLOCK
CHARGE/DISCHARGE
COUNTER
R2
LBI
R3
1.8V/2.0V
FULL CCMD DCMD BBON
LBO
R_BBON
Figure 1. Functional Diagram
_______________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
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