UC2906

UC3906

Sealed Lead-Acid Battery Charger

FEATURES

•

Optimum Control for Maximum

Battery Capacity and Life

•

Internal State Logic Provides

Three Charge States

•

Precision Reference Tracks

Battery Requirements Over

Temperature

•

Controls Both Voltage and

Current at Charger Output

•

System Interface Functions

•

Typical Standby Supply

Current of only 1.6mA

DESCRIPTION

The UC2906 series of battery charger controllers contains all of the necessary

circuitry to optimally control the charge and hold cycle for sealed lead-acid batter-

ies. These integrated circuits monitor and control both the output voltage and cur-

rent of the charger through three separate charge states; a high current

bulk-charge state, a controlled over-charge, and a precision float-charge, or

standby, state.

Optimum charging conditions are maintained over an extended temperature

range with an internal reference that tracks the nominal temperature charac-

teristics 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 sup-

ply 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 implement a low current turn-on mode of the charger,

preventing high current charging during abnormal conditions such as a shorted

battery cell.

Other features include a supply under-voltage sense circuit with a logic output to

indicate when input power is present. In addition the over-charge state of the

charger can be externally monitored and terminated using the over-charge indi-

cate output and over-charge terminate input.

BLOCK DIAGRAM

SLUS186 - SEPTEMBER 1996