Analyzing false turn-on events with varying gate drive parameters in high voltage GaN devices

Abstract

In this paper, we address the problem of false turn-on effects in a half-bridge GaN power converter in terms of circuit and device parameters. The model shows that the inherent false turn-on problem is caused by slew rates $\frac{d{v}_{\mathrm{ds}}}{\mathrm{dt}}$ and $\frac{d{v}_{\mathrm{gs}}}{\mathrm{dt}}$during the switching transients occurring at the turn-on and off phases. A higher slew rate propagates the gate driver voltage to overshoot beyond the threshold voltage causing it to accidentally turn on This study shows that $\frac{d{v}_{\mathrm{ds}}}{\mathrm{dt}}$ is dependent on the internal device parameters such as $g_{\mathrm{fs}}$ (transconductance) and $C_{\mathrm{oss}}$(output capacitance). From the CV characteristics, it is pretty much evident that the internal capacitances $C_{\mathrm{oss}}$and $C_{\mathrm{rss}}$ (reverse transfer capacitance) are reduced with higher drain voltage enabling higher slew rates which increases the probability of false turn-on problems. Experimental results at numerous operating points at 400 V with the variation in different gate drive parameters support the analysis.