A 6.78-MHz Single-Stage Wireless Charger With Constant-Current Constant-Voltage Charging Technique

A 6.78-MHz fully integrated single-stage wireless charger with constant-current constant-voltage (CC-CV) charging technique for resonant wireless power transfer applications is presented. Based on the principle of three-mode reconfigurable resonant regulating ( $R<^>{3}$ ) rectifier, the proposed charger achieves high efficiency and low cost by realizing power rectification, voltage regulation, and CC-CV charging in a single power stage. The power stage of the proposed charger consists of only four nMOS power transistors. A bootstrapping technique using a single-input-dual-output voltage doubler with adaptive phase control is also proposed to integrate bootstrap capacitors on-chip. The CC loop and the CV loop share the same pulsewidth modulation (PWM) controller with smooth transition from the CC mode to the CV mode. An on-chip current sensing and estimation circuit is specially designed for the CC loop. Fabricated in a standard 0.35- $\mu \text{m}$ CMOS process with a die area of 8 mm(2), the charger delivered a maximum charging current of 1.5 A, and the measured peak efficiency reached 92.3% and 91.4% when the charging currents were 1 A and 1.5 A, respectively.