A Scalable Multiphase Current-Mode Buck Controller With Sub-Milliohm DCR Current Sensing and Synchronized Overcurrent Protection

This article presents a scalable multiphase peak current-mode Buck controller with sub-milliohm direct current resistance (DCR) current sensing and synchronized overcurrent protection. Low DCR current sensing capability is critical in pursuing high efficiency and precise current balancing. For this purpose, a sub-milliohm DCR current sensing circuit is proposed. The low-frequency current signals from all the phases are amplified by a time-shared amplifier, and the outputs are combined with the exaggerated high-frequency signals, respectively, to rebuild the proportional current sensing signals. The small signal analysis and the design guidelines of the proposed sensing scheme are presented. The proposed current sensing scheme enhances the signal-to-noise ratio, improves the phase to phase current balancing, and dramatically reduces the silicon area of the sensing circuit. A latch-up problem of hiccup mode over current protection in the multi-chip parallel system is addressed in this article. A synchronized hiccup mode over current protection scheme is designed to solve the issue without adding extra communication bus to the system. The proposed controller is fabricated using a 0.6- \mu \text{m} BiCMOS process, and the experimental results prove the effectiveness of the current sensing circuit and protection scheme.