GaN Driving Techniques and Circuits for High Performance and High Reliability Power Electronics

High frequency DC-DC converters have gained more popularity due to the ever-increasing demand on fast transient response, small solution size and high-power density in power systems. However, as the switching frequency is pushed high up to tens of MHz, the power efficiency is greatly compromised due to a significantly increased switching loss in conventional silicon based solutions. To mitigate this challenge, it is widely believed that Gallium Nitride (GaN) technology would replace conventional silicon technology due to the far superior figure of merits. However, due to the strict requirements on high reliability, high efficiency and low EMI noise in automotive applications, the GaN based DC-DC converter faces new challenges. Therefore, a family of high frequency GaN driver or GaN based DC-DC converter solutions have been developed to address the main design challenges before their wide use in automotive.

In this research, a wide input, high reliability GaN gate driver is firstly developed in automotive applications. An active BST balancing scheme is presented to adaptively control the BST charging by directly sensing VSW, and achieve a constant BST rail voltage to prevent GaN from VGS breakdown. With IO/VIN-sensed VSW dual-edge tdead modulation, tdead is adaptively adjusted to achieve ZVS turn-on of MH and ML to improve efficiency.

To overcome the EMI challenges in high frequency operation, a tri-slope gate driving GaN DC-DC converter for EMI-regulated automotive electronics is presented. A spurious noise compression technique is proposed to compress and evenly redistribute the spurious noise within a defined frequency sideband, achieving significant EMI noise reduction at main switching frequency and its harmonics. Meanwhile, a tri-slope gate driver is proposed to control the voltage and current slew rates of GaN switches for effective ringing suppression, which is adaptive to load and input voltage changes.

To alleviate the ground noise interference and high frequency switching challenges, an on-die ground isolated GaN driver is presented. The ON-duty mirrors adaptively map the ON-duty times of the gate signals from respective input signals to maintain same ON-duty times, and the self-excited tdead minimizers minimize the tdeads between the high side and low side channels. Meanwhile, an on-die ground isolation technique maintains robust states of gate drive signals against DC ground shifting, AC ground bounce and high dv/dt transient at VSW.

All the proposed GaN gate drivers and GaN based DC-DC converters have been fabricated, tested to demonstrate the presented schemes or techniques in this research. The effectiveness of the design is successfully verified in the measurement results, not only in steady state, but also in transient scenarios. The high reliability, high efficiency and low EMI performance has been successfully verified to enable the high frequency GaN DC-DC converters for automotive use.