Small-Signal Modeling and Loop Analysis of Ultrafast Series Capacitor Trans-Inductor Voltage Regulator With Constant On-Time Control

In this article, a comprehensive small-signal model is developed for multiphase series capacitor trans-inductor voltage regulator (SCTLVR) with current mode constant-on time (CMCOT) control. The transfer function of the power stage is thoroughly derived by decoupling the SC structure and the trans-inductor. The modeling of the CMCOT modulator is conducted using the describing function (DF) method, known for its high accuracy, particularly in the high-frequency domain. This method ensures precise prediction and analysis of the dynamic response. To address the demands of ultra-high current applications, the model is extended to accommodate multiple modules, allowing for a detailed closed-loop analysis. Validation through SIMPLIS simulations and experimental results demonstrates the model's accuracy and reliability. The established model provides qualitative guidance on optimally designing the SCTLVR controller under various operating conditions.

I. Introduction

With the rapid evolution of artificial intelligence (AI), GPU accelerators feature an outstanding thermal design power, and require efficient, compact, and ultra-fast dynamic response [1], [2], [3]. As the bus voltage of data center motherboards shifts from to [4], there is a pressing need for power supplies that can achieve higher voltage step-down ratios while maintaining ultra-fast dynamic response () at the load point. However, these new requirements present challenges for conventional Buck converters. A higher voltage step-down ratio results in increased switching stress and losses. In addition, to enhance dynamic response, the number of Buck phases must be increased, leading to larger volume and potential instability.