Li-Ion Cell Charger Has Charge Termination Circuitry, Needs No FET

Capable of delivering up to 800 mA of charge current, the LTC4054 is a linear charger for single-cell, 4.2V Li-ion and Li-polymer batteries. The IC packs charge termination circuitry plus a power transistor, eliminating the need for an external FET. And by also eliminating the need for a sense resistor and blocking diode, the 5-lead SOT-23 device enables designers to build a complete charger that occupies just 18 mm2 of board real estate and that stands only 1 mm high. The LTC4054 cell charger also offers a thermal feedback regulation feature to prevent overheating, as well as a feature for keeping the battery "fresh" after charge termination—it does this by monitoring battery voltage and automatically recharging the battery if the voltage drops below a set threshold. The chip operates from a 4.25V to 6.5V supply and charges batteries in a constant-current/constant-voltage mode and terminates charging after detecting C/10. Termination is indicated by a charge status pin, which can signal a µC or drive a LED. The user sets the charge current with a resistor. The IC costs $1.40 each/1,000. For more details, call Afshin Odabaee at LINEAR TECHNOLOGY CORP., Milpitas, CA. (408) 432-1900, ext. 2593.