Solar energy harvesting system with integrated battery management and startup using single inductor and 3.2nW quiescent power

This paper presents a 3.2nW quiescent power solar energy harvesting system. The control circuit is designed in an asynchronous fashion that scales the effective switching frequency of the converter with the level of the power transferred. The on-time of the converter switches adapts dynamically to the input and output voltages for peak-current control and zero-current switching. The chip integrates self-startup, battery management, supplies 1V regulated rail with single inductor and supports power range of 10nW to 1μW. For input power of 500nW, the proposed system achieves an efficiency of 82%, including the control circuit overhead, while charging a battery at 3V from 0.5V input. In buck mode, it achieves a peak efficiency of 87% and maintains efficiency greater than 80% for output power of 50nW-1μW with input voltage of 3V and output voltage of 1V.