In order to increase the efficiency of modern microprocessors power supplies used in data-centers, 380 V dc power distribution system have been attracting attention for their high efficiency and high-reliability. This paper presents an innovative single-stage approach for the 380 V voltage regulator modules (VRM) based on a quasi-resonant multilevel topology constant on-time (COT) operation. The proposed topology inherently integrates the multiphase approach, providing fast phase shedding and flat high efficiency curves even at light load conditions. This is a unique advantage, which is not possible to establish in the two stage approach, which is very important in server architectures, and where high efficiency is required even at light load conditions. The paper analyses the circuit topology and proposes a control architecture for fast transient response, including the current sharing capabilities. The digital controller has been implemented in 0.16 μm lithography together with a digital pulse width-modulation (DPWM) with a 195 ps resolution, and a 40 MS/s, 7-bit ADC. Experimental results show an efficiency of 93% for a 120 A, 380 V-1.8 V VRM power supply.