A Continuously-Scalable-Conversion-Ratio Step-Up/Down SC Energy-Harvesting Interface With MPPT Enabled by Real-Time Power Monitoring With Frequency-Mapped Capacitor DAC

Yeohoon Yoon, Hyungmin Gi, Jongmin Lee, Minsik Cho, Changyoun Im, Yongmin Lee, Chisung Bae, Sang Joon Kim, Yoonmyung Lee

Abstract: An energy-harvesting interface that incorporates a continuously scalable-conversion-ratio (CSCR) switched-capacitor (SC) dc-dc converter with maximum power point tracking (MPPT) is introduced in this paper. By exploiting unique characteristics of a CSCR SC converter, an MPPT based on the hill climbing algorithm is implemented with a real-time power monitoring scheme with a frequency-mapped sampling capacitor DAC, allowing variation-tolerant MPPT for various types of energy sources. The harvestable voltage range is significantly extended by a step-up/down convertible CSCR SC converter, and the voltage conversion efficiency is further improved with matrix-structured and load-mapped power switches. With the test chip fabricated in 28nm FDSOI technology, the proposed energy harvesting interface shows peak conversion efficiency of 89% and average efficiency of > 80% for 60-2, $794~\mu \text{W}$ . MPPT efficiency of > 97 % is confirmed with energy harvesting measurement with a solar cell.