Analysis and Design of Ultrafast Series Capacitor Trans-Inductor Voltage Regulator With Constant On-Time Control

In this article, a multiphase series capacitor trans-inductor voltage regulator (SCTLVR) based on constant on-time control in data center point-of-load applications is proposed. The series capacitor structure divides the high input voltage among each Buck cell, effectively doubling the equivalent step-down ratio and duty cycle while halving the switch voltage stress. In addition, the output inductors are indirectly coupled through an electrical connection. Benefiting from low equivalent transient inductance and current-mode constant on-time (CMCOT) control, it demonstrates an ultrafast dynamic response. Both steady-state and transient operations are thoroughly analyzed. This article provides a detailed analysis of the design considerations for the SCTLVR, which employs CMCOT control. A 24 V input, 1.2 V output, and 120 A rated prototype is designed to validate the proposed concept. This prototype achieves 91.1% peak efficiency and demonstrates exceptional dynamic response under 1000 A/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>s current slew rate. The voltage overshoot and undershoot are less than 2% of the nominal output value. The experimental results align closely with the theoretical analysis.