Imbalanced High-Current Multi-Phase Buck Converters for High-Performance CPUs

Abstract

High-performance CPUs require buck converters with high-current ratings (4-12 A), fast dynamic response, and high efficiency across a wide load range. The most common approach for realizing such buck converters is the conventional multi-phase topology with phase-shedding, where all the active phases are identical in terms of the inductor, the switching frequency, and the share of the total load current, i.e. balanced phases. Instead, this paper proposes using a different inductor, switching frequency, and share of the total load current for each individual phase, i.e. imbalanced phases. This approach provides additional degrees of freedom by the independent choice of the inductor and the switching frequency of each phase, which enables higher maximum load current rating and higher efficiency across the entire load current range compared to conventional balanced multi-phase designs. To demonstrate the viability and the advantages of imbalanced multi-phase buck converters in high-current application, a 12-A 4-phase design in 0.13-µm CMOS for high-performance CPUs is presented and compared to three conventional balanced reference designs in the same process technology.