Digital control of resonant converters at ultra high frequency

Voltage regulators (VRs) powering microprocessors face stringent requirements on size; response; and efficiency. Current-type resonant converters, like the series resonant converter are particularly well-suited for these applications as they are able to achieve efficient high frequency operation, and have a capacitive output filter. However, despite their merits, they are often overlooked because of size and performance issues associated with their control. In this paper, variable frequency pulse density modulation (VF-PDM) control of the series resonant converter (SRC) is presented to enable resonant converter benefits to be realized in VR applications. It achieves efficient multi-megahertz switching frequency, ultra-fast transient response with minimal filter capacitance, and is inherently stable. It will be shown that with proper converter design, these benefits can be achieved with a simple, low clock rate digital controller.