MAX1538 Datasheet, PDF (1/22 Pages) Maxim Integrated Products – Power-Source Selector for Dual-Battery Systems

19-3169; Rev 0; 1/04
Power-Source Selector for
Dual-Battery Systems
General Description
The MAX1538 selector provides power-source control
for dual-battery systems. The device selects between
an AC adapter and dual batteries based on the pres-
ence of the three power sources and the state of
charge of each battery. The MAX1538 includes analog
comparators to detect AC/airline-adapter presence and
determine battery undervoltage. Fast analog circuitry
allows the device to switch between power sources to
implement a break-before-make time, which allows hot
swapping of battery packs. The MAX1538 indepen-
dently performs power-source monitoring and selec-
tion, freeing the system power-management µP for
other tasks. This simplifies the development of µP
power-management firmware and allows the µP to enter
standby, reducing system power consumption.
The MAX1538 supports “relearn mode,” which allows
the system to measure and fully utilize battery capacity.
In this state, the part allows the selected battery to be
discharged even when an AC adapter is present. The
MAX1538 can also be used to power the system in an
aircraft. On detecting an airline adapter, the MAX1538
automatically disables charging or discharging of bat-
tery packs and only allows the system to be powered
from the adapter.
The MAX1538 is available in a space-saving 28-pin thin
QFN package with a maximum footprint of 5mm x 5mm.
Applications
Notebook and Subnotebook Computers
Internet Tablets
Dual-Battery Portable Equipment
Pin Configuration appears at end of data sheet.
Features
♦ Automatically Detects and Responds to
Low-Battery Voltage Condition
Battery Insertion and Removal
AC-Adapter Presence
Airline-Adapter Presence
♦ Step-Down and Step-Up Charger Compatibility
♦ Fast Break-Before-Make Selection
Allows Hot Swapping of Power Sources
No External Schottky Diodes Needed
♦ 50µA Maximum Battery Quiescent Current
♦ Implements Battery Capacity Relearning
♦ Allows Usage of Aircraft Supply
♦ Direct Drive of P-Channel MOSFETs
♦ Simplifies Power-Management µP Firmware
♦ 4.75V to 28V AC-Adapter Input Voltage Range
♦ Small 28-Pin Thin QFN Package (5mm x 5mm)
Ordering Information
PART
MAX1538ETI
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
28 Thin QFN
Typical Operating Circuit
BATTERY
CHARGER
CHG_OUT
ACDET
AIRDET
CHRG
BATSEL
ADPIN
RELRN
OUT2
REVBLK
OUT1
OUT0
EXTLD
MAX1538
ADPBLK
V_DD
CHGIN
CHGA
CHGB
DISB
DISA
MINVA
MINVB
GND
BATB
BATA
BATSUP
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