Tiny rechargeable SMD micro-batteries for emergency backup power

Backup power supplies are used to keep some key electronic functions running in case of failure or shut down of the main power. Their main requirements depend on the application:

- to backup RTC or microcontrollers (µC), the key is to store enough energy to cover the quiescent current of the RTC or the deep-sleep current of the µC. In some industrial applications like Programmable Logic Controllers (PLC), it is required to keep the RTC active several weeks after the main power shutdown, between -40° and 85°C.

- to backup volatile memories in PLC and enterprise SSD, high power is required to keep the content of cache/buffer memories or complete their data transfer to non-volatile memories.

Today, the backup functions are:

- either primary coin cells that do not deliver peak currents, are bulky, do not operate beyond 60°C, and are assembled manually

- or supercapacitors that are expensive, bulky, self-discharge quickly and have aging problems

The proposed solution is based on solid-state micro-batteries featuring  footprints of less than 8mm² and volumes of less than 12mm3 (much smaller than supercapacitors)). They are delivered in SMD outlines and are compatible with automated PCB assembly lines (pick & place, reflow soldering). The broadest operating temperature range is up to -40°C 85°C. These are long lifespan batteries (10-20 years) and feature self-discharge rate of less than 5%/month compatible with long backup times of industrial PLC.

These micro-batteries are not only able to store high energy densities but also to deliver high peak currents (a few 100 milliampers) and the power of 0,1W to 0,5W over 150 to 400ms typically required to transfer a cache/buffer content into a non volatile memory.

This solution combines the best of battery and supercapacitor performance:a single component is enough to backup simultaneously RTC and µC and DRAM/SRAM and enterprise/client SSDs as well.