LAUSR

Fully integrated on-time-based mode control is utilized to achieve an efficient mode control of a PWM/PFM mode buck converter for implantable medical devices. The proposed method predicts load current from the on-time of the power switches of the buck converter and does not require an additional current sensor. Additional passive components for load current estimation are not required in this approach. Moreover, this method consumes less control power and requires a smaller area compared with other circuits used for load current prediction. The proposed dual mode buck converter is fabricated using TSMC $0.18~\mu \text{m}$ CMOS technology. The active chip area is 0.58 x 0.46 mm2. The input voltage range is 2.2–5.0 V, the output voltage is 1.8 V, and the load current range is 0.2–100 mA. The experimental results demonstrate the proper mode transition under step-up/down load current transient. The peak power conversion efficiency was approximately 94 % at 50 mA, and the minimum efficiency was approximately 77 % within the load current range.