A 400 V Dual-Phase Series-Capacitor Buck Converter GaN IC with Integrated Closed-Loop Control

GaN high-electron-mobility transistors (HEMTs) offer a 13× better $R_{\text{DS,on}}Q_{g}$ figure-of-merit than silicon LDMOS for power converters operating above 100 V. Recent GaN manufacturing advancements allow monolithic integration, merging sensing, protection, and control circuits with high-voltage GaN HEMTs. This paper presents a fully monolithic closed-loop series-capacitor buck converter for 200 V-to-5V and 400 V-to-12V direct conversion. The presented design manages closed-loop control complexity, overcoming challenges in analog and digital GaN circuitry and reducing static power consumption. A unique switching sequence eliminates the need for a level shifter, addressing challenges associated with common-mode transient immunity and high $dv/dt$ signals. Converter operation is experimentally validated up to 400 V. The on-chip closed-loop control regulates the 5V output voltage to within 410mV under a load step from light-load to 0.4 A. The design achieves a competitive power density of 2.17 W/cm3, delivering 13.7W at 400 V-to-12V and attains a peak efficiency of 80.2% for 200 V-to-5V operation. This work represents the first demonstration of closed-loop control with an integrated multi-phase half-bridge capable of operating at 400 V.