Lithium-ion charger dedicated to preserving eCall batteries in vehicles

September 22, 2014 // By Graham Prophet
ISL78692 is a battery charger IC with very low leakage current; it is specifically designed to extend the life of an eCall (automatic emergency call system) backup battery when vehicle battery is off.

The 4.1V charger has lower leakage current (3 µA) than alternative solutions, allowing the backup battery to remain charged for a longer period of time. Lower charging voltage also extends battery life while the device's small footprint reduces total solution size.

Vehicles equipped with eCall systems automatically place a call to an emergency service centre in the event of an accident. The ISL78692 Li-ion battery charger is designed to support emerging worldwide emergency call systems such as Europe’s eCall initiative, which brings rapid assistance to motorists involved in a collision anywhere in the European Union, and OnStar, which provides a safety and security service in the United States.

The ISL78692 charger’s ability to monitor the battery’s temperature and its low, 4.1V output voltage both help to extend the life of, specifically, LiFeP04 (lithium-iron-phosphate) batteries, which are commonly used in this function. Highly integrated, the ISL78692 requires five external components to program the charging current. When combined with the charger’s 3 x 3 mm DFN package, the complete solution fits on space-constrained PCBs. The ISL78692 also offers a unique charge current thermal foldback feature that prevents overheating by automatically reducing the battery charging current, creating a very robust, small footprint design. It also pre-conditions, with a trickle-charge, a cell that has been deeply discharged.

The part is a complete charger for single-cell Lithium batteries; it has 3 µA leakage (max) over -40°C to 85°C temperature range; will supply up to 1A programmable charging current; and allows trade-off of battery charging time against heat dissipation and expected battery lifetime. I has guaranteed operation down to 2.65V after start-up, preventing shut off during cold-crank start; and 1% initial voltage accuracy provides precise control of charging level to extend operating lifetime of the battery. Power transistor and current sensor are integrated. A 10% trickle charge preconditions a fully drained battery until it reaches 2.8V minimum charge level; an NTC thermistor input protects battery by