Serial-Stacked Single-Inductor Dual-Source Triple-Output Energy Harvesting Interface With 2D-MPPT for Battery-Free IoT Devices

This paper presents a dual-source energy harvesting interface for battery-free IoT devices, utilizing a serial-stacked single-inductor triple-input triple-output (SS-SITITO) buck-boost converter topology. In each charging cycle, the converter allows simultaneous power extraction from two energy harvesting sources and the usage of recycled energy in a storage capacitor. A two-dimensional maximum power point tracking (2D-MPPT) with triple-modulation realizes 98.3% accuracy in tracking the maximum power point for each input with minimal power cost. To provide sufficient output power under limited inputs, the system features energy recycling by automatically switching between sleep and active modes, and introduces a quad-phase buck-boost operation scheme, achieving up to 26mW maximum output power. To ensure self-sustainability with low quiescent power and enhanced power conversion efficiency, the circuit incorporates an edge-triggered feedback path, a power-optimized undervoltage lockout circuit, a low-voltage-supportable bandgap reference generator, and an ultra-low-power relaxation oscillator. Experimental results show a quiescent power consumption of 805nW, a 7000x power range, and a peak efficiency of 85.5%.