LT1239

Obsolete: Datasheet For Information Purposes Only. Contact Analog Devices for Potential Replacement

The LT1239 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 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 powered by the 5V supply.

A comparator is included which provides automatic switchover from main 5V power to backup power ensuring uninterrupted power for memory and power monitoring circuitry. A low-battery detector with a 5V threshold powers down the second regulator and the error amplifier to limit the discharge voltage of the backup cells. This prevents deep discharge damage to the lithium cells. Both regulators have independent shutdown and current monitor functions.

Applications

• Backup Battery Management Systems for Portable Computers
• Lithium-Ion Backup Systems
• NiCd Backup Systems