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The continuous built-in resistance detection (CBIRD) is proposed in the switching-based charger system to achieve fast charging. Corresponding to built-in resistance (BIR) variation of Li-ion battery and charging current limitation from input energy, the CBIRD dynamically adjusts the transition voltage at the constant current (CC) mode. As a result, the transition timing from CC mode to the constant voltage (CV) mode can be postponed. Rated large charging current and extended period in CC mode effectively reduce charging time. Besides, the proposed automatic energy deliver control (AEDC) technique considers both loading system and battery status simultaneously to manage charging current according to the loading system's requirement and input supply energy for high efficiency charging. The proposed switching-based charger system was fabricated in 0.25 μm CMOS process and occupied 3 mm2 silicon area. The charger system can save up to 40% of charging time. The charger system achieves 87% of peak power efficiency at a rated 1 A charging current.