A 100-mV–2.5-V Burst Mode Constant on-Time- Controlled Battery Charger With 92% Peak Efficiency and Integrated FOCV Technique

In this paper, a burst mode constant ON-time-controlled, energy harvesting charger is presented. The proposed boost converter system uses the burst mode control to improve the efficiency by 11%, compared to the conventional single-mode energy transfer implementation with an ultralow-power input comparator. A technique to deduce an optimum inductor energizes time across the given input range, for which the maximum converter efficiency is demonstrated. An internally triggered, capacitor-less sample-and-hold block addresses the leakage issue in the conventional fractional open-circuit voltage maximum power point tracking systems. The system is capable of charging a super-capacitor of 4.7 mF, from 1.8 to 3.3 V from an input power of 50 μW to 100 mW by maintaining the maximum power at the input. The entire system is designed and fabricated in the standard 180-nm CMOS technology, and the measurement results show a peak efficiency of 92% at 98-mW input power for the output voltage of 3 V and efficiency ≥65% across the range of input voltages more than 0.3 V for the output voltage of 1.8 V.