Zero Current Detector with Slope Judgement Calibration in Mobile Battery Charger IC

Depending on a type of input sources, a mobile battery charger IC operates as a buck converter to charge the battery from travel adapter (TA), and a boost converter to supply the load current of USB On-The-Go (OTG) from the battery, respectively. For both converter operations, a zero current switching (ZCS) is important to achieve high conversion efficiency. However, because operating voltage and current change continuously as both battery and input status, the optimal ZCS condition is not constant. Although several techniques in [1–3] have been reported to automatically calibrate ZCS operation, the additional freewheeling power switch should be used in [1, 3]. In addition, these works used the current sensor that would be sensitive to various operating condition, such as process, supply voltage, and temperature (PVT) variation. This paper proposes a zero current detector (ZCD) with a slope judgement calibration. The slope value of switching node $(V_{LX})$ is used to accurately judge ZCS condition, resulting in both conversion efficiency improvement and robust operation in PVT.