Present-day mobile platforms call for a compact power management solution due to the necessity of packing ever increasing functionality into a very constrained form factor. The conventional buck/boost converter suffers from bulky magnetics with its compromise between the size of passives and the performance. The emerging switched-capacitor (SC) converter shows great potential for a fully integrated solution with the on-die capacitor. However, the intrinsic charge sharing in a SC converter leads to an efficiency and power density trade-off which inhibits its application in the battery powered devices that demands more than a few watts. In addition, a SC converter is only efficient at a discrete conversion ratio determined by its topology. The voltage regulation over a wide range usually comes at the cost of efficiency degradation.

As a way to mitigate the limitation of the inductor-based and switched-capacitor based converter, we explore the resonant switched capacitor (ResSC) topology as a hybrid approach. The ResSC topology can utilize the favorable on-die capacitor for tight integration while leveraging a small inductor to eliminate the intrinsic charge sharing. This enables higher power density without efficiency compromise along with lossless regulation. The introduced inductance is much less than that needed in the common buck/boost converter. In order to facilitate the design and control of a ResSC converter, the harmonic-balance method is adopted for developing its large signal and small signal models. A current-phase based compensation scheme based on the small signal model is developed to enable a fast transient response. The effectiveness of topology concept, modeling and control are verified by the switched-based simulation in a design example for on-chip power delivery.




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