400mA synchronous buck battery charger accepts up to 40V

August 08, 2014 // By Graham Prophet
LTC4121 is a constant-current/constant-voltage 400 mA charger for Lithium-Ion, LiFePO4 and lead-acid batteries. The LTC4121’s high efficiency, synchronous step-down topology accepts a wide 4.4V to 40V input. A programmable 3.5V to 18V battery charge voltage range with tight ±1% accuracy makes the LTC4121 suitable for a variety of battery chemistries.

The fixed output float voltage version, LTC4121-4.2, is suitable for 1S lithium-ion battery packs. A synchronous architecture enables charging efficiency up to 94% as well as low dropout start-up and operation. Typical applications include handheld instruments, solar-powered devices, as well as industrial and military sensors and devices.

To accommodate high impedance input sources such as solar panels, the LTC4121 can regulate its input voltage to a programmable percentage of the input open circuit voltage. If the input voltage falls below the user-defined percentage of the open circuit voltage, charge current will be automatically reduced. This maximum power point tracking (MPPT) technique enables maximum power operation with a variety of high impedance input sources, even in non-ideal operating environments.

The LTC4121 features programmable charge current from 50 mA to 400 mA and low voltage battery preconditioning. A recharge function starts a new charging cycle if the battery voltage drops 2.2% below the programmed charge voltage. Safety features include a two-hour termination timer as well as NTC temperature qualified charging. Two open-drain outputs provide charge and fault status information.

The LTC4121 is housed in a low profile (0.75 mm) 16-pin 3 x 3 mm QFN package with exposed pad for thermal performance, for operation from -40°C to 125°C in both E and I grades. It costs $2.60 (1,000)

Linear Technology; www.linear.com/product/LTC4121