Research On 600V Depletion Mode GaN HEMT Negative Voltage Gate-Drive Technology

With the continuous maturity of GaN technology,its application field has gradually expanded from low-voltage(LV)and low-power systems under 100 V to high-voltage(HV),high-power and high-power density systems over 400 V.The advantages of the physical characteristics of the HV GaN device make it a solution for HV power conversion system to replace the traditional super-junction MOSFET.However,the traditional driver for HV Si power devices cannot fully match the performance advantages of HV GaN devices,and the LV GaN driver and system scheme are not applicable under HV.Therefore,the design of high reliability,HV and high performance GaN driving system has become the key to the development of current HV GaN technology.The design of the driving circuit is directly determined by the physical mechanism of the power device.This paper makes an in-depth exploration of the physical mechanism of E-mode(Enhancement mode),D-mode(Depletion mode)and Cascode(cascade type)HV GaN devices,and analyzes and summarizes the current driving strategies,advantages and design challenges of the three devices from the academia and the industry.Comprehensive consideration of FOM value,high dv/dt immunity ability,gate voltage range,slew-rate control and device reliability,this paper selects D-mode GaN as the power device,designing the HV Driving System based on Direct-drive driving strategy.Aimed at the drawbacks of the LV GaN driving system under HV application,optimization and improvement measures for HV GaN driving system are put forward first.Isolated gate-drive technique based on capacitance coupling isolation and magnetic coupling isolation are further discussed,then summarizes the signal transmission modes of the two isolation scheme,the isolated HV half-bridge driving system architecture is designed at the system level.For the thermal management of high power GaN power converter,the design of bottom cooling and top cooling schemes of the surface paste package is studied.Based on the system requirements of Direct-drive driving strategy of D-mode GaN devices,this paper proposes a Negative Directly Gate-drive technology and designs a single channel 600 V power level integrated driver chip.In order to achieve high reliability,high efficient power supply,a Low Dropout Regulator(LDO)with over current limit function is designed.For the negative threshold voltage characteristic of D-mode GaN,an Inverting Buck Boost is designed to provide a negative gate-drive voltage for turn-off.For the switching mechanism of D-mode GaN,a Tri-slope gate-drive circuit suitable for D-mode GaN is designed based on the Adjustable Drive-slope Control technology.For the system reliability during the power-on stage,an Enabled MOS protection scheme cascaded with D-mode GaN is designed.The above circuit design schemes are based on 0.35?m 60 V BCD process,and the integration verification of the chip is completed under the Double-pulse Test and Half-bridge Driving Scheme.The simulation results show that the performance indexes of the chip based on the proposed scheme are in line with the expectation at 400 V input voltage and 1MHz switching frequency.