A Monolithic GaN-Based Driver and GaN Power HEMT with Diode-Emulated GaN Technique for 50MHz Operation and Sub-0.2ns Deadtime Control

Abstract

Monolithic gallium-nitride (GaN) high-electron-mobility transistors (HEMTs) have become popular due to their low parasitic capacitance, low on-resistance (R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> ), and no reverse recovery charge loss for high-frequency and high-power-density applications [1]–[6]. However, GaN HEMTs have several process defects [7], such as trapping effect and reverse-conduction loss, which will reduce the efficiency of GaN-based converters. Referring to Fig. 14.1.1, during the deadtime, the VSW falls to negative voltage before low-side GaN HEMT (Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> ) becomes conductive. Even without a body diode, Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> will experience “self-commutation loss” when the voltage difference between its gate and drain exceeds the threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH, E(650V)</inf> ). The overall efficiency decreases since GaN HEMTs have higher source-to-drain voltage drop (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD</inf> ) as compared to the body diode voltage of silicon MOSFETs. Although the power converter presented in [5] uses adaptive deadtime control to achieve a 3% efficiency improvement, due to the unpredictable delay of discrete control, the load-dependent deadtime is still not well controlled. Moreover, considering high switching operation, high dVsw/dt will cause gate ringing problem in switching period. At bottom middle of Fig. 14.1.1, the conventional negative turn-off gate bias and high drain voltage will cause a large electric field between gate and drain, thereby inducing serious trapping effect (bottom left of Fig. 14.1.1). The monolithic GaN driver with adaptive source current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">lCTRL</inf> ) does not consider the parasitic effects during turn-off period (bottom right of Fig. 14.1.1) [1].