Integrated GaN Power Conversion: Topology, Reliability and Implementation


December 2021


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The explosive growth of power electronics has resulted in high power demand and more stringent requirements on power conversion systems. When bridging an increasing high input voltage and a decreasing low output voltage, high step-down ratio power converters demand high power density, high reliability, and high integration level. Compared to classic silicon power devices, new arising gallium nitride (GaN) technology presents the superior figure of merits, and it is regarded as a more promising power device candidate to overcome these challenges. However, because of the high step-down conversion ratio and unique characteristics of GaN power devices, GaN-based dc-dc power conversions face new challenges. Thus, a series of integrated GaN power conversion topologies, schemes and implementations have been explored to address power density, reliability and integration challenges. Firstly, a GaN-based double step-down (DSD) power topology is presented for direct 48V/1V power conversion. In order to realize closed-loop regulation of the DSD power converter, an adaptive ON- and OFF-time (AO2T) control with elastic ON-time modulation is developed for both steady state regulation and transient response enhancement. To reinforce the dual-phase operation reliability of the DSD converter, a master-phase mirroring technique enables adaptive master-slave phase operation, accomplishing automatic phase current balancing. Secondly, to improve the system reliability of automotive electronics, a low EMI noise high stepdown ratio GaN-based buck converter is designed for direct battery-to-load power conversion. It employs an anti-aliasing multi-rate spread-spectrum modulation (MR-SSM) technique to suppress EMI noise and an in-cycle adaptive zero-voltage switching (ZVS) technique to minimize switching losses. Compared to the classic fixed-rate SSM (FR-SSM), the MR-SSM technique adaptively spreads EMI spectra in a wider frequency range without aliasing spikes and, thus, reduces peak EMI noise more effectively. To improve efficiency, an elastic dead-time (tdead) controller facilitates in-cycle adaptive ZVS despite of a continuous switching frequency variation. For the enhancement of GaN power devices driving reliability, a pulse-reinforced level shifting technique is proposed to immune high switching node voltage dv/dt transition. Thirdly, to enhance the GaN power device reliability of GaN-based power conversion system, an on-chip self-calibrated full-profile dynamic on-resistance sensing strategy is proposed to monitor the online healthy state of power devices. It achieves instant dynamic on-resistance sensing beyond megahertz. Moreover, complicated high-speed current sensing circuits are avoided to reduce implementation cost, and the random sensing errors are calibrated automatically for high sensing accuracy. The online state-of-health condition of GaN-based power converter is thus monitored comprehensively, precisely, and efficiently. Finally, one monolithic integrated e-mode GaN asymmetrical half-bridge (AHB) power converter is implemented for direct 48V/1V power conversion, which minimizes non-ideal parasitics, enhances power conversion reliability, and reduces system complexity significantly. In the AHB converter, an auto-lock auto-break (A2 ) level shifting technique is developed to address the challenges of pull-up performance, device breakdown risk and dv/dt immunity at switching node voltage. The self-bootstrapped hybrid (SBH) gate driving technique adaptively achieves rail-torail dynamic gate driving in normal operation and robust static gate driving during large transients. The on-die temperature sensing facilitates hot spot monitoring and thermal management for high reliability. In this dissertation, all the proposed GaN dc-dc power converters have been fabricated and tested to demonstrate the proposed system topologies, control schemes, circuit techniques. The measurement results successfully validate the effectiveness of the designs. The high switching frequency, low EMI noise, high reliability, and monolithic integration have been verified to enable GaN dc-dc power conversions.



Engineering, Electronics and Electrical