We present a fully integrated multimode lithium-ion battery charger integrated circuit (IC) for wirelesspower charging applications. The proposed charger IC integrates an analog block for battery charging, a digital control block, an analog-to-digital converter, and memory on a single chip. To improve the charging efficiency, the supply voltage of the charger IC is controlled by an adaptive low-dropout (LDO) regulator. A series-voltage feedback path is formed along the LDO regulator and multimode level shifter, which regulates the supply voltage to closely follow the battery voltage.

For a smooth transition during multimode charging, we propose a new approach for built-in resistance compensation. The digital control block of the charger IC is designed in accordance with the Qi standard. The battery charger IC is fabricated in a one-poly six-metal 0.18-μm CMOS process. Integrated with the digital control block and memory, the core area of the multimode charger IC is 0.9 × 1.4 mm2. The input voltage ranges from 4.8 to 5 V. The output voltage is 4.2 V in constant-voltage mode. The charging current in constant-current mode is 450 mA. The maximum and average charging efficiencies are 83% and 79%, respectively.