DESCRIPTION
The LT ®1239 is a micropower backup battery management system for portable computers and instrumentation. It contains two regulators for regulating the battery voltage and memory voltage and a comparator for switching 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 providesaregulatedbackupbatteryvoltagetothememory 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 powered by the 5V supply.

FEATURES
■ Micropower Operation (IQ = 20μA)
■ 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
■ Backup Battery Management Systems for Portable Computers
■ Lithium-Ion Backup Systems
■ NiCd Backup Systems