Energy-Harvesting PMIC: Battery-less / Ultra-Low-Power IoT with the EM Micro EM8500
Energy harvesting frees sensors from battery swaps: ambient energy (solar/thermal) → an energy-harvesting PMIC → storage → an ultra-low-power load, at µW–mW scale. This guide covers how to select an energy-harvesting PMIC (cold-start, MPPT, storage, rails, Iq), using the EM Micro EM8500 (0.3V cold-start, HW MPPT, dual storage, 4 rails, 125nA) as the worked example, paired with the EM6819 MCU.
What is energy harvesting? Four stages
Energy harvesting is the technique of scavenging tiny amounts of ambient energy to power a device, freeing sensors from the fate of periodic battery replacement. An energy-harvesting system has four stages: an ambient energy source (solar/photovoltaic, thermal/TEG, vibration/piezo, RF) → an energy-harvesting PMIC (which conditions the weak, unstable energy, does maximum-power-point tracking and up/down conversion) → an energy buffer (capacitor / supercap / rechargeable cell) → an ultra-low-power load (sensor + BLE/LPWAN). Set the scale first: ambient harvesting is a microwatt-to-milliwatt (µW–mW) game — enough for a duty-cycled wake-sense-and-transmit burst, not for continuously powering a high-power load.
What an energy-harvesting PMIC does
The energy-harvesting PMIC is the heart of the system, and it must do several things: cold-start — start itself from a source that is nearly dead and at a very low voltage, with no battery; MPPT (maximum power point tracking) — keep the source at its most efficient operating point to extract the most energy; up/down conversion — boost the weak input to a usable rail; energy-storage management — charge and protect the buffer cap/cell; and provide regulated output rails to the load. The key selection specs revolve around these: cold-start voltage/power, supported source types and power range, MPPT method, storage-element support, number of output rails, and the chip's own quiescent current (Iq).
The EM8500's key specs
Take EM Microelectronic's EM8500 (a DC energy-harvesting controller, targeting DC sources like photovoltaic/solar and thermoelectric/TEG): it cold-starts as low as VIN ≈ 0.3V / ~3µW, and once running keeps harvesting down to ~0.1V / 1µW; it has a fully embedded, programmable hardware MPPT whose target ratio is configurable 50%–88% (≈50% for TEG, ≈80% for solar); storage uses a dual Long-Term Storage (LTS) + Short-Term Storage (STS) architecture, where STS speeds start-up when the LTS is empty, supporting a primary cell, rechargeable cell, and super/gold-caps, with under/over-voltage protection; it provides 4 configurable output rails + sleep gating; its own quiescent current is about 125nA (very low — note some distributor pages mislabel it 25nA; use the datasheet's 125nA); interface SPI/I²C, plus an integrated USB fast-charge, a luxmeter and configurable wake-up; package QFN24 4×4mm. (Note: the figures above are cross-confirmed from Digi-Key / the indexed datasheet text; confirm exact values and per-rail current against EM Micro's own datasheet.)
How to choose + the EM8500 pairing
How to choose an energy-harvesting PMIC? First, look at cold-start, not efficiency — if it can't start at your dimmest light / smallest ΔT with no battery, nothing else matters (the EM8500's 0.3V/3µW is aggressive). Second, match MPPT to the source — a programmable ratio (EM8500's 50–88%) beats a fixed MPPT when you might use either solar or TEG. Third, demand storage flexibility + protection — dual storage lets you pair a supercap (instant-on) with a rechargeable/primary cell (energy density), with under/over-voltage protection for the cell. Fourth, count the rails and gating — put the power-hungry radio on an independently switchable rail so you can duty-cycle it. Fifth, keep Iq far below the power you harvest (the EM8500's ~125nA is the energy floor). For pairing, the EM8500 + EM Micro's ultra-low-power MCU EM6819 (0.9–3.6V, ~400nA in power-down) + a low-power radio (BLE/LPWAN) is a sensible battery-less node (a logical pairing, not an official reference design).
⚠️ Realistic expectations and supply
Two realistic reminders. One, energy harvesting is a µW–mW affair — a small indoor solar cell or a body-heat TEG yields microwatts to low milliwatts, enough for a duty-cycled wake-and-transmit, not continuous high power; design around energy-per-event, not continuous current. Two, the EM8500 targets DC sources (solar/TEG); for RF, piezo or AC vibration you must add a rectifier front-end first. Also, the EM8500 is marked Discontinued at some distributors — confirm availability and lifecycle status before designing it into a new product. Fits: battery-less / long-life sensors, wireless switches and asset trackers where battery replacement is impractical. JLink Technology is an authorized EM Microelectronic distributor supplying the energy-harvesting PMIC (EM8500) and the ultra-low-power MCU (EM6819); tell us your energy source, power budget and load, and we will help assess feasibility and selection, and reply with samples, datasheets and pricing.
Products mentioned
EM8500 Ultra-Low Power Energy-Harvesting PMIC
The EM8500 is an energy-harvesting power-management IC from EM Microelectronics that draws power from µW–mW sources such as solar cells or thermoelectric generators (TEG). Its boost converter cold-starts from 300mV / ~3µW with embedded maximum-power-point tracking (MPPT), and provides 4 independently configurable outputs — the heart of battery-less or battery-extended IoT sensor nodes.
EM6819 Ultra-Low Power 8-bit MCU
The EM6819 is an ultra-low power 8-bit RISC microcontroller from EM Microelectronics. Built on CMOS process, it operates down to 0.9V and achieves nA-level sleep current. Features integrated LCD driver, timers, ADC, and rich peripherals — ideal for battery-powered consumer electronics and smart card applications.
TLM922S LoRa / LoRaWAN Module
The TLM922S is a LoRaWAN-certified module from KIWI Technology integrating a Semtech SX1272 LoRa transceiver and a 32-bit MCU (Cypress S6E1C32) running the LoRaWAN stack, controlled over a UART AT-command interface. 902~928MHz (US915-class), up to +20dBm output, ~10km line-of-sight range — for LoRaWAN IoT nodes, smart metering, and asset tracking.
Need these components or design help?
JLink Technology provides parts, datasheets, and engineering support.
Request a Quote