Comprehensive Analysis and Improvement Methods of Noise Immunity of Desat Protection for High Voltage SiC MOSFETs With High DV/DT

Abstract

This paper comprehensively analyzes desaturation (desat) protection for high voltage (>3.3 kV) silicon carbide (SiC) MOSFETs and especially how to build in noise immunity under high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> . This study establishes a solid foundation for understanding the trade-offs between noise immunity and response speed of desat protection. Two implementations of the desat protection for high voltage SiC MOSFETs are examined, including desat protection based on discrete components and desat protection realized with a gate driver integrated circuit (IC). Both positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> and negative <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> are investigated. Analysis results show that the high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> with long duration caused by high voltage SiC MOSFETs’ switching results in strong noise interference in the desat protection circuitry. The impact of numerous influencing factors is investigated analytically, such as parasitic capacitances, parasitic inductance, damping resistance, and clamping impedance. Under high positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> , extremely small parasitic capacitances (<0.01 pF) between the drain terminal and protection circuitry could still compromise noise immunity of the desat protection circuitry that has a high-impedance voltage divider. Comprehensive design guidelines are summarized to boost the noise immunity, including circuit design, component selection, and PCB layout. The noise immunity margin under the positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> is also derived quantitatively to guide the noise immunity improvement. The noise immunity analysis results and noise immunity improvement methods are validated with simulation and experimental results obtained from a phase leg based on 10 kV/20 A SiC MOSFETs.