An Autonomous Energy Harvesting Power Management Unit With Digital Regulation for IoT Applications

Efforts towards energy-harvesting solutions are targeted for wireless sensor node applications and focus on performing maximum power extraction and storing power, yet efforts to deliver a regulated supply to voltage-sensitive blocks in power-limited applications has yet to be fully achieved. This paper presents a low-power, autonomous power management unit (PMU) able to perform maximum power point tracking for dc-type renewable sources. It includes a startup circuit fed directly from the renewable source. The PMU delivers a regulated output voltage through a digital LDO. The main step-up operation is performed through a dynamically controlled, power-aware, capacitive dc-dc converter that performs the required voltage gain procedure. Then, the digital LDO receives the EH source power density information from the dc-dc converter and provides regulation. Information about the source-power density availability is passed on to the digital LDO in order to select the best pass device size from a bank of three arrays. The PMU allows power consumption decrease by reducing the gate driving losses associated with large pass transistor devices, and it enhances efficiency. The system was fabricated in 180 nm CMOS process, and maximum end-to-end efficiency was measured at 57% with 1.75 mW of input power.