Resonant Drive Optimization for Synchronous Rectifiers in High-Current and Ultra-Low-Voltage LLC DCX

Voltage regulator modules (VRMs) that power artificial intelligence processors demand ultralow voltage and extremely high current outputs. The LLC dc transformer (DCX) is a widely adopted solution in VRMs, but suffers from significant synchronous rectifier (SR) driving losses. Furthermore, the conduction loss of SRs is found to be highly sensitive to driving speed under ultralow voltage and high current output conditions, which has not yet been thoroughly investigated. For the first time, the reverse conduction characteristics of SRs are measured and modeled, transitioning from channel conduction to body diode conduction. Using the developed model, the impact of driving speed on both SR conduction loss and driving loss is analyzed in detail. A co-optimization method for reducing SR conduction and driving losses with resonant drive is proposed. A 40-1V/200A LLC DCX circuit is constructed and experimentally validated. Compared to traditional hard drive methods, the peak efficiency and full-load efficiency with the optimized resonant drive are improved by 3.2% and 1.1%, respectively. Additionally, the resonant drive circuit is designed to be highly compact, occupying only 6% of the total board area.