LT1239_15 Datasheet, PDF (1/12 Pages) Linear Technology – Backup Battery Management Circuit

OBSOLETE:
FOR INFORMATION PURPOSES ONLY
Contact Linear Technology for Potential Replacement
FEATURES
I _{Micropower Operation (IQ = 20µA)}
I _{Adjustable Regulator for Battery Charging}
I _{4.85V Regulator for Battery Regulation}
I _{Cell Voltage Equalization in 2-Cell Systems}
I _{Low-Battery Detector Protects Lithium Cells}
I _{Comparator for Automatic Power Switching}
I _Shutdown
I _{Output Current Sensing}
I _{Current and Thermal Limiting}
I _{Reverse Output Protection}
I _{16-Pin SO Package}
I _{Operates on 7V to 30V Input}
U
APPLICATIONS
I _{Backup Battery Management Systems for Portable}
Computers
I _{Lithium-Ion Backup Systems}
I _{NiCd Backup Systems}
LT1239
Backup Battery
Management Circuit
DESCRIPTION
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
Lithium-Ion Backup System
MAIN
BATTERY
PACK
7V TO 24V
10
INPUT 2
INPUT 1
14
+
22µF
SHDN1
3
GND ₂
GND ₄
IN
LOW-BATTERY
DETECT
GND
GND ₅
IN _REGULATOR OUT
#2
SHDN2
6
GND
I_MON2
11
REGULATOR
#1
INPUT 2
–
OUT 1
16
ADJ
1
I_MON1
15
E/A (IN)
7
8
+
E/A (OUT)
INPUT 1
+
5V_IN
13
–
OUT 2 ₁₂
120Ω* 120Ω*
300pF
604k ⁺
1%
22µF
69.8k
1%
681k
1%
3.4V
Li-Ion
CELL
5V SYSTEM
POWER
3.4V
Li-Ion
CELL
MEMORY
POWER
MANAGEMENT
* REQUIRED BY SOME SAFETY AGENCIES
SEE APPLICATIONS INFORMATION
FOR INFORMATION ON
SELECTING VALUES.
LTC1239 • TA01
1