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Hybrid Switched-Capacitor/Buck Converter Voltage Regulator Disclosure Number: IPCOM000247030D
Publication Date: 2016-Jul-27
Document File: 7 page(s) / 958K

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"A Hybrid SC/Buck Converter combines transistors of a switched capacitor stage with a buck converter stages so that the transistors are used for both capacitor switching and buck conversion. This reduces the overall number of transistors that would otherwise be required for separately realized stages, which, in turn, reduces board space required for a particular voltage regulator application."

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Hybrid Switched-Capacitor/Buck Converter Voltage Regulator

A two-stage power delivery architecture has a switched capacitor converter for a first stage and a buck converter for a second stage. In some of these architectures, the first stage, the switched capacitor converter, relies primarily on capacitive energy transfer. The output of the first stage is then provided to a buck converter to generate a point of load voltage.

The operational modes and switching states of the switched capacitor converter and the buck converter may facilitate the low voltage side field effect transistors (FETs) in the switched capacitor converter to be reused with phase legs in the buck converter. An architecture that utilizes the low voltage side FETs in the switched capacitor converter as the phase legs in the buck converter is referred to as a hybrid switched-capacitor/buck converter voltage regulator, or simply a "hybrid SC/Buck converter." One example architecture is illustrated in Fig. 1 below.

Fig. 1: Example Hybrid SC/Buck Converter

In Fig. 1, FETs Qp_* are cooperatively switched in a manner that causes them to perform both in a switched capacitor converter role and in a buck converter role. By doing so, the current flowing in each Qp_* FET will carry two components: (1) a current of the switched capacitor converter; and (2) an output inductor current of the buck converter. As a result, the architecture

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allows for the reduction of a total number of FETs, which, in turn, reduces both costs and board space requirements. For example, a total size of a 48V to Point-of-Load power delivery system can be reduced by 15%-20% when compared to a system that utilizes entirely separate switched capacitor and buck converter stages.

When the FETs are combined as described above, the switched capacitor converter operates at a duty cycle of the buck converter, e.g., 20%. This results in an increase of RMS current in the switched capacitor FETs. When the duty cycle of the switched capacitor FETs is reduced, the resonant frequency of the switched cap converter increases. As a result, the passive components, such as flying capacitor sizes and resonant inductor sizes, in the switched capacitor converter are also reduced. This can result in another reduction in size, e.g., another 15%-20% reduction in board space requirements when compared to a system that utilizes entirely separate switched capacitor and buck converter stages.

Furthermore, should the switched capacitor portion be a resonant switched capacitor converter and utilize stray inductance as an inductive component, it n...