Contact Linear Technology for Potential Replacement
FOR INFORMATION PURPOSES ONLY
OBSOLETE:
LT1239
Backup Battery
Management Circuit
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Micropower Operation (I
Q
= 20
µ
A)
Adjustable Regulator for Battery Charging
4.85V Regulator for Battery Regulation
Cell Voltage Equalization in 2-Cell Systems
Low-Battery Detector Protects Lithium Cells
Comparator for Automatic Power Switching
Shutdown
Output Current Sensing
Current and Thermal Limiting
Reverse Output Protection
16-Pin SO Package
Operates on 7V to 30V Input
APPLICATIONS
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Backup Battery Management Systems for Portable
Computers
Lithium-Ion Backup Systems
NiCd Backup Systems
The LT
®
1239 is a micropower backup battery manage-
ment system for portable computers and instrumenta-
tion. It contains two regulators for regulating the battery
voltage and memory voltage and a comparator for switch-
ing between main power and backup power. The first
regulator provides a constant voltage charge for the
backup batteries and is adjustable from 3.75V up to 20V.
An equalization amplifier combined with the first regulator
provides precision charge equalization for a 2-cell
lithium-ion system. A second regulator with 4.85V output
provides a regulated backup battery voltage to the memory
when main power is lost. The second regulator also
isolates the backup battery from the main 5V supply
during normal operation when the memory is being pow-
ered by the 5V supply.
A comparator is included which provides automatic
switchover from main 5V power to backup power ensur-
ing uninterrupted power for memory and power monitor-
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
U
Lithium-Ion Backup System
INPUT 2
14
22µF
3
SHDN1
INPUT 1
10
OUT 1
REGULATOR
#1
ADJ
I
MON1
E/A (IN)
INPUT 2
GND
2
IN
LOW-BATTERY
DETECT
GND
16
1
15
7
681k
1%
8
3.4V
Li-Ion
CELL
13
5V SYSTEM
POWER
69.8k
1%
120Ω* 120Ω*
604k
1%
300pF
MAIN
BATTERY
PACK
7V TO 24V
+
E/A (OUT)
5V
IN
GND
4
GND
5
IN
REGULATOR
#2
OUT
INPUT 1
+
–
GND
OUT 2
12
MEMORY
POWER
MANAGEMENT
* REQUIRED BY SOME SAFETY AGENCIES
SEE APPLICATIONS INFORMATION
FOR INFORMATION ON
SELECTING VALUES.
LTC1239 • TA01
6
SHDN2
I
MON2
11
U
FEATURES
DESCRIPTION
+
–
U
+
22µF
3.4V
Li-Ion
CELL
1
LINER [ LINEAR TECHNOLOGY ]
