1FEATURES
• 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

SUPPORTS DEFENSE, AEROSPACE,
AND MEDICAL APPLICATIONS
• Controlled Baseline
• One Assembly/Test Site
• One Fabrication Site
• Available in Military (–55°C/125°C)
Temperature Range(1)
• Extended Product Life Cycle
• Extended Product-Change Notification
• Product Traceability
• Not to Exceed 185.35-KHz Oscillation
Frequency at 125°C

DESCRIPTION
The UC2909 controls lead acid battery charging with a highly efficient average current mode control loop. This
chip combines charge state logic with average current 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 –3.9-mV/°C thermistor linearization circuit,
voltage and current error amplifiers, a PWM oscillator, a PWM comparator, a PWM latch, charge state decode
bits, and a 100-mA open collector output driver.