UC3906 Gell Cell Power Controller.

The UC3906 battery charger controller incorporates all of the necessary circuitry to control the charge and hold cycle for sealed lead-acid batteries.
The UC3906 monitors and controls both the output voltage and current of the charger through three individual charge states:
A high current bulk-charge state
A controlled over-charge state
A precision float-charge, or standby, state.
Preferred charging conditions are maintained over an extended temperature range with an internal reference that tracks the nominal temperature characteristics of the lead-acid cell. A typical standby supply current requirement of only 1.6mA allows these ICs to predictably monitor ambient temperatures.
Separate voltage loop and current limit amplifiers regulate the output voltage and current levels in the charger by controlling the onboard driver.
The driver will provide up to 25mA of base drive to an external pass device. Voltage and current sense comparators are used to sense the battery condition and respond with logic inputs to the charge state logic. A charge enable comparator with a trickle bias output can be used to activate a low current turn-on mode of the charger, preventing high current charging during unusual conditions such as a shorted battery cell.
The UC3906 also features a supply under-voltage sense circuit with a logic output to indicate when input power is available. In addition the over-charge state of the charger can be externally monitored and terminated using the over-charge indicate output and over-charge terminate input.