LT1239CS pdf daa:
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-ing circuitry. A low-battery detector with a 5V threshold prevents deep discharge damage to the lithium cells. Both powers down the second regulator and the error amplifier regulators have independent shutdown and current moni-
to limit the discharge voltage of the backup cells. This tor functions.