Power Management for µW to mW Energy Harvesting Systems

The EM8500 from EM Microelectronics, a Swatch Group company, is an integrated power management solution for low power applications. It is specifically designed for efficient operation with a variety of dc harvesting sources including thermal electric generators (TEG) or photovoltaic (solar) sources in the µW to mW range.

The device is designed to speed-up system start-up time when the main energy storage element (aka Long Term Storage – LTS) is completely discharged or insufficiently charged to supply the application, by using a secondary energy storage element (Short Term Storage - STS). When using a non-rechargeable primary battery the EM8500's onboard PMU offers a mechanism to extend battery life when assisted by a harvesting element.

The EM8500 incorporates a boost converter able to start with an input voltage as low as 300mV and an input power of few μW. In functional mode the EM8500 operates at energy levels from a dc harvesting source as low as 100mV and 1μW. To maximize harvesting efficiency the EM8500 integrates a programmable maximum power point tracking controller.

The EM8500 is capable of working with a variety of energy elements as secondary storage, namely re-chargeable batteries, super-capacitors or conventional capacitors. In all cases the EM8500 maintains its fast start-up capability that depends only on the harvester conditions and the STS capacitor value.

A USB connection to an external power source is available on the EM8500 for fast charge of the long term storage element. The EM8500 integrates voltage supervisory functions. Minimum and maximum voltages are controlled on the LTS element to prevent damage to the energy storage element. Harvester minimum voltage monitoring allows stopping the dc-dc limiting power loss when no energy can be harvested. Output voltages are kept in a safe range for the application.

To perform granular power management of the application, the EM8500 integrates four independent supply outputs and a sleep mode offering the capability to switch off part or all the supplies. The EM8500 is available in an industry standard QFN24 4x4 package as well as in bump form.