UC2909

UC3909

DESCRIPTION

The UC3909 family of Switchmode Lead-Acid Battery Chargers accurately

controls lead acid battery charging with a highly efficient average current

mode control loop. This chip combines charge state logic with average cur-

rent PWM control circuitry. Charge state logic commands current or voltage

control depending on the charge state.

The chip includes undervoltage

lockout circuitry to insure sufficient supply voltage is present before output

switching starts. Additional circuit blocks include a differential current sense

amplifier, a 1.5% voltage reference, a –3.9mV/°C thermistor linearization

circuit, voltage and current error amplifiers, a PWM oscillator, a PWM com-

parator, a PWM latch, charge state decode bits, and a 100mA open collec-

tor output driver.

Switchmode Lead-Acid Battery Charger

FEATURES

• Accurate and Efficient Control of

Battery Charging

• Average Current Mode Control from

Trickle to Overcharge

• Resistor Programmable Charge

Currents

• Thermistor Interface Tracks Battery

Requirements Over Temperature

• Output Status Bits Report on Four

Internal Charge States

• Undervoltage Lockout Monitors VCC

and VREF

1/99

BLOCK DIAGRAM

UDG-95007-1

Pin numbers refer to J, N, DW packages.