Ultra-Low-Power Switched-Capacitor DC-DC Converters
Michael Douglas Seeman and Seth R. Sanders
California Energy Commission
Switched-capacitor power converters have been used in IC designs for years, but the fundamentals of the converters' operation have not been well defined. This research formally specifies the structure of switched-capacitor converters and develops a method for easily determining the performance of these converters. These performance metrics can be used to optimize component values in converters as well as to compare different converter topologies. The analytical tools developed will aid construction of several switched-capacitor circuits .
The first IC we built using a switched-capacitor converter is an integrated switched-capacitor DC-DC converter for use with the PicoCube project. The PicoCube system uses an average of 6 microwatts at very low duty cycles (high relative peak power) at three voltage rails. This converter will rectify an energy scavenger source and supply the three voltage rails from a single small rechargeable battery. An integrated circuit implementing this converter has been designed, manufactured, and tested. Peak efficiencies of 80% have been obtained through empirical results .
In the future, multi-level switched-capacitor circuits will be considered. Instead of being limited to a single conversion ratio, these enhanced topologies can efficiently be configured to produce a wide range of conversion ratios. The applications of such a converter are widespread. They have been typically used as inverters to drive motors or to create other ac waveforms. However, they can also be used to add efficient regulation to typical DC-DC applications. An IC using a multilevel switched-capacitor converter will be fabricated in future work.
- M. D. Seeman and S. R. Sanders, "Analysis and Optimization of Switched-Capacitor DC-DC Converters," IEEE COMPEL, July 2006.
- M. D. Seeman, S. R. Sanders, and J. M. Rabaey, "An Ultra-Low-Power Power Management IC for Wireless Sensor Nodes," IEEE CICC, September 2007.