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

Monolithic gallium-nitride (GaN) high-electron-mobility transistors (HEMTs) have become popular due to their low parasitic capacitance, low on-resistance (RON), 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 (QL) becomes conductive. Even without a body diode, QL will experience 'self-commutation loss' when the voltage difference between its gate and drain exceeds the threshold voltage (VTH, E(650V)). The overall efficiency decreases since GaN HEMTs have higher source-to-drain voltage drop (VSD) 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 (IlCTRL) does not consider the parasitic effects during turn-off period (bottom right of Fig. 14.1.1) [1].