On-Chip HV Bootstrap Gate Driving for GaN Compatible Power Circuits Operating Above 10 MHz

With superb device characteristics, gallium nitride (GaN) power transistors facilitate fast and efficient power conversion and delivery in modern power circuits. To take full advantage of these devices, high switching frequency ( $f_{\mathrm {SW}}$ ) operation is highly desirable. However, the lack of GaN compatible high-speed, efficient, and reliable gate drivers has been a formidable design hindrance. In this article, we address three critical design challenges faced in GaN power gate driving, namely bootstrap (BST) level-shifting, switching slew rate (SR) control, and active deadtime $t_{\mathrm {dead}}$ control. We first propose a BST dynamic level-shifting technique to enable sub-nanosecond $t_{\mathrm {delay}}$ at high $f_{\mathrm {SW}}$ . Meanwhile, a dual-SR switching technique is introduced to retain both low switching power and noise. Compared with traditional constant $t_{\mathrm {dead}}$ controls, the $t_{\mathrm {dead}}s$ in this design are regulated actively for high efficiency. To validate these techniques, a four-phase GaN-based switching power converter was designed and implemented on a $0.35~\mu \text{m}$ high-voltage (HV) BCD process. At a $f_{\mathrm {SW}}$ of 20 MHz and a $V_{\mathrm {IN}}$ of 20 V, it delivers a maximum power of 8.4 W and a peak efficiency of 84.9%. The gate drivers are fully integrated including all BST capacitors and active BST switches. It achieves regulated rise and fall $t_{\mathrm {dead}}s$ of 3.2 and 4.7 ns, respectively, for a load range from 50 mA to 1.2 A. The gate switching rise time $t_{R}$ is reduced to 1 ns with a maximum switching SR of 48 V/ns. The converter employs a HV synchronized hysteretic control, which works with the proposed gate drivers seamlessly to demonstrate a dynamic voltage scaling (DVS) Vo up- and down-tracking speeds of $0.33~\mu \text{s}$ /V and $0.47~\mu \text{s}$ /V, respectively.