Multiple-Input Harvesting Power Management Unit With Enhanced Boosting Scheme for IoT Applications.

Powering Internet of Things sensor nodes in the expanding application platforms requires a highly efficient power management unit (PMU), with adaptive power consumption based on harvester energy availability and load conditions. To provide continuous reliable operation, this paper presents a PMU, which is able to extract energy from four energy sources, while providing independent maximum power point tracking (MPPT) for each harvester. With MPPT being achieved independent of voltage boosting, a novel step-up ratio technique is implemented for enhancing charging time and efficiency by 33.5% (3.5×). A fully digital technique to detect harvester energy flow is designed to scale down system power during energy drought periods, while being able to cold-start from inputs as low as 0.4 V. The stored energy is used by load through a hybrid analog–digital linear dropout regulator (LDO) or further boosted for pulsed battery charging. The chip is fabricated in the 180-nm process with an area of 0.46 $\text{mm}^{2}$ and achieves a maximum power delivery of 2.6 mW and a maximum end-to-end efficiency of 70% at 40 $\mu \text{W}$. [ABSTRACT FROM AUTHOR]