A 97.1% Buck-Boost Battery Charger with a Constant Current Extension Technique for 2x Faster Battery Charging with Accurate Termination of Charging Process

With portable devices requiring more power and efficiency, there is an increasing demand for larger battery capacities and faster charging solutions [1]. The battery charging process comprises three stages: pre-charge, constant current (CC), and constant voltage (CV). The conventional charging profile is depicted at the top of Fig. 1. Achieving fast charging depends on the transition point from CC to CV mode. The built-in resistance detection (BIRD) technique can efficiently extend CC mode and reduce CV mode duration, thereby shortening the charging time [2–3]. However, the accuracy of BIRD is limited due to variations in the built-in resistor $\left(R_{B I R}\right)$ with temperature and state of charge (SOC) changes. Consequently, the inaccuracies introduced by BIRD result in an extended CV duration. Simultaneously, the conventional architecture faces challenges in accurately distinguishing between small charging current and termination current due to noise, resulting in premature termination and inefficiency in CV mode. Insufficient charging will significantly reduce battery capacity, with just 0.1 V of undercharging, a 4.2 V lithium-ion battery will cause a 10% capacity loss [4]. Therefore, the proposed constant current extension (CCE) technique introduces additional CC time in CV mode to reduce $C V$ charging time for fast charging and ensure high efficiency and accurate termination time.