Variable frequency buck-boost converter for high efficiency voltage stacked systems

Abstract

The rise of mobile technologies and cloud computing has increased the importance of efficient energy consumption. Due to parallelism, high voltage conversion ratios, and large supply currents, power losses are rapidly increasing. This issue can be managed by on-package voltage stacking, where the current is recycled between multiple cores. Current mismatch between serially connected cores however produces a noise voltage between the cores. Differential power processing (DPP) converters are a potential solution to this issue. In the current work, a power efficient, load-to-load synchronous buck converter operating within a voltage stacked system is examined. The buck converter is evaluated under very high current demand, where the core currents in a voltage stacked system reach a tenfold difference. A compact model to characterize the voltage drop in serially stacked systems is also described. Furthermore, a circuit topology to increase the power efficiency of this converter is proposed. By using an interleaved system with different active phases, the inductance in the converter can be changed, which produces variable frequency operation, resulting in increased power efficiency due to lower switching losses. The power efficiency of the converter is increased by up to 8% as compared to constant frequency operation, achieving a range between 89% to 99%.