A Design Methodology for Switched-Capacitor DC-DC Converters

Abstract

Switched-capacitor (SC) DC-DC power converters are a subset of DC-DC power converters that use a network of switches and capacitors to efficiently convert one voltage to another. Unlike traditional inductor-based DC-DC converters, SC converters do not rely on magnetic energy storage. This fact makes SC converters ideal for integrated implementations, as common integrated inductors are not yet suitable for power electronic applications. While they are only capable of a finite number of conversion ratios, SC converters can support a higher power density compared with traditional converters for a given conversion ratio. Finally, through simple control methods, regulation over many magnitudes of output power is possible while maintaining high efficiency. A complete, detailed methodology for SC converter analysis, optimization and implementation is derived. These methods specify device choices and sizing for each capacitor and switch in the circuit, along with the relative sizing between switches and capacitors. This method is advantageous over previously-developed analysis methods because of its simplicity and the intuition it lends towards the design of SC converters. The strengths and weaknesses of numerous topologies are compared amongst themselves and with magnetics-based converters. These methods are incorporated into a MATLAB tool for converter design. This design methodology is applied to three varied applications for SC converters. First, a high-voltage hybrid converter for an autonomous micro air vehicle is described. This converter, weighing less than 150mg, creates a supply of 200V from a single lithium-ion cell (3.7V) to supply the aircraft's actuators. Second, a power-management integrated circuit (IC) is presented for a wireless sensor node. This IC, with a target quiescent current of 1 uA, supplies the system voltages of the PicoCube wireless sensor node. Finally, the initial design of a high-current-density SC voltage regulator is presented for low-footprint microprocessor applications.