Ultra-low-profile Single-stage Voltage Regulator Module (VRM) for Next-generation AI Accelerators

This paper presents an ultra-low-profile single-stage voltage regulator module (VRM) for next-generation AI accelerators. The proposed solution employs a cascaded transformer-coupled VRM topology, which can improve the effective duty cycle of power transistors, ensuring high-efficiency operation at large voltage transfer ratios. The proposed coupling transformer achieves a transient inductance of 13nH per phase and a steady-state inductance of 68nH per phase, which can reduce the current ripple in stable operation and provide rapid dynamic response during load transition. A prototype with 400A output current is constructed and tested. The thickness of the prototype is 3.9mm, allowing it to be mounted underneath the AI accelerator for vertical power delivery. The prototype features a peak efficiency of 89% and full-load efficiency of 81% at 54V-0.8V voltage transfer ratio. Dynamic response to fast load transition is critical for AI accelerators. In this paper, an evaluation board equipped with load steppers is designed and implemented to experimentally validate the dynamic performance of the VRM prototype.