Built-in resistance compensation (BRC) technique for fast charging Li-Ion battery charger

This paper presents a BRC technique to speed up the charging time of the Li-Ion battery. Based on the physical properties of the battery cell, the charger circuit charges the cell with three stages, which are trickle current (TC), constant current (CC), and constant voltage (CV) stages. Due to the internal parasitic resistance of the Li-Ion battery pack system, the charger circuit switches from the CC stage to the CV stage without fully charging the cell to the rated voltage value. At the CV stage, the cell is needed to be charged by a degrading current. The longer the cell stays at the CV stage, the longer the charging time is due to the degrading current. The BRC technique can dynamically estimate the internal resistance of the battery pack system to extend the period of the CC stage. The test chip was fabricated in TSMC 0.35-mum process. Experimental results show the period of the CC stage can extended to about 40% that of the original design. The charging time can be effectively reduced.