Steady state analysis & design of switched capacitor DC-DC convertors

This paper presents a new approach to modelling switched capacitor (SC) DC-DC power converters in the steady-state. The distinguishing feature of SC DC-DC converters, i.e., no inductance elements and therefore the relationship in electricity quantity among the component capacitors can be determined, is made full use of, thus the analysis is much simplified. The analysis results reveals that a SC DC-DC converter can work in three modes, i.e. PWM mode, FM mode and transition mode. Boundary conditions of the three modes are derived. Behavior of a SC DC-DC converter in CCS (continuous charging situation) and DCS (discontinuous charging situation) are found to be quite different. A unified equivalent circuit for SC DC-DC converters is obtained which shows that the regulation on a SC DC-DC converter is always accompanied with energy losses. Therefore, an unregulated SC part with a cascade low drop linear regulator is the optimum topology. Finally the analyzed results are verified by experiments.