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
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.