Bootstrap Operation in eGaN-Based Full-Wave ZCS Quasi-Resonant Synchronous Buck Converter for Server Application

In the current power architecture of server mother-boards, synchronous buck converters (SBCs) are used as point-of-load (POL) power supplies for low-voltage, high-current CPU rails. Due to hard-switching transitions in SBCs, these POLs not only incur high switching loss but cause significant EMI emissions as well. This high-frequency noise emission impacts the digital communication between the POLs and the CPU. This issue is typically addressed either by adopting advanced device structure or sophisticated noise cancellation techniques or by introducing additional circuit overheads. But these approaches either increase the complexity of IC design and fabrication or compromise the POL efficiency. An alternative solution to this problem could be to introduce soft-switched quasi-resonant SBCs for POL application. But the possibility of incorporating bootstrap gate driving in these topologies needs to be explored. This paper presents bootstrap operation in full-wave ZCS quasi-resonant synchronous buck converter (FWZCS QRSBC). Detailed mode analysis is performed, which reveals soft-switching in the bootstrap diode for FWZCS QRSBC. The details of component placement and PCB layout are presented for an e-GaN-based experimental prototype that facilitates both SBC and FWZCS QRSBC modes of operation. SIMPLIS simulation and experimental results are presented to compare the bootstrap performance in SBC and FWZCS QRSBC.