Controller Design and Phase Current Balancing for Fast Dynamic Performance in Voltage Mode Controlled Multiphase Buck Converters

With the growing computational requirement in powerful digital processors in modern smartphone and automotive applications, multiphase buck converters remain an attractive power management solution to achieve higher efficiency over a wide load current range with better thermal distribution and faster load as well as DVS transient performance with the reduced output capacitor. Also, a high switching frequency is desirable for a smaller form factor, which makes it difficult to sense fast-changing phase currents. Fixed frequency voltage mode control (VMC) remains a cost-effective solution in terms of phase shifting and phase shading; however, the challenges remain in achieving fast transient performance and accurate phase current balancing. This paper considers a VMC multiphase buck converter and proposes a novel current balancing method and controller tuning algorithm to achieve fast transient with accurate phase current balancing for master-master VMC configuration. Small-signal-based PID and type-III compensator design methods are considered for the controller design. Finally, a large-signal based PID controller is computed, which can significantly improve the transient performance and is demonstrated using simulation results. A four-phase buck converter prototype is fabricated, and a few experimental results are presented.