Research And Design Of High-Frequency Automotive GaN Half-Bridge Driver

Automotive applications require power converters to support wide input voltage range because the voltage of 12-V in-vehicle battery can vary from 3 to 40V due to transient loads such as cold-cranks and load dumps.Meanwhile,the switching frequency of power converters is typically higher than 2MHz in order not to generate electromagnetic interference（EMI）in the sensitive amplitude modulation（AM）radio working band（530k Hz-1.8MHz）in vehicle.It is far from meeting the strict needs for conventional power MOSFETs in automotive applications.Gallium Nitride（Ga N）high electron mobility transistors（HEMTs）are promising power devices due to their excellent characteristics.However,Ga N HEMTs have vulnerable gates which are susceptible to noise and voltage spikes,limiting their implementation in power converters.This thesis presents a Ga N half-bridge driver aiming at high switching frequency automotive applications.The driver introduces active clamping scheme based on high-side voltage sensing with low power consumption,which could adaptively clamp the bootstrap rail voltage at an appropriate level with acceptable voltage ripples.Meanwhile,dual level shifters（DLS）scheme is applied in both the high-and low-side driving path to effectively drive the Ga N HEMTs with low propagation delay and high dv/dt immunity.Simulation results reveal that the bootstrap rail voltage could be clamped at an average voltage of 5.25V when operating from 2MHz to 10MHz in a Ga N-based buck converter which converts from 12V to 3.3V.And the voltage ripple ranges from 58m V to 134m V with maximum voltage ripple ratio of 2.55%in typical conditions.And the minimum regulating period of high-side active clamping scheme is 2.7μs,which is slower relatively compared to the megahertz-level switching frequency of a buck converter.Meanwhile,the total power consumption of high-side active clamping circuit is only 0.4m W,which is much smaller than conventional Zener diode clamping scheme that usually needs to consume several tens of milliwatts of power and thus is energy saving.The peak source and sink current of output stage are 1.787A and 4.569A respectively,which helps to drive high current rating Ga N HEMTs.And the propagation delay for both the high-and low-side driving path is about 17ns with Ga N HEMTs as loads in system simulation.The proposed driver is fabricated in 0.18-μm high voltage（HV）Bipolar-CMOS-DMOS（BCD）process with 2.72-mm² active die area and a fully integrated HV Schottky diode serving as a bootstrap diode.The driver supports 5-18V input voltage range.Testing results have shown that the typical propagation delay with empty load for the driving path is 16ns and could support 2-10MHz operating.The bootstrap rail voltage could be clamped at the range from 5V to 5.5V effectively even the switching node voltage V_SW is pulled down to–1.58V and the voltage ripple varies from 40m V to 158m V.Thus,the safety of high-side Ga N HEMT could be guaranteed.A buck converter utilizing this driver with Ga N HEMTs could achieve maximum efficiency of91.58%in the 16.5-W output power range when operating at 2MHz,which is superior to conventional silicon-based power converters and suitable for automotive applications.The testing results are approximate to simulation results as well as demonstrate the effectiveness of the proposed design.