A buck-boost negative shutdown voltage generation circuit was designed. By introducing a dynamically adjustable off-time timing module, a segmented current-limit module and a ripple based high speed detection module, a stable negative gate voltage supply was achieved during the fast switching of depleted GaN devices, which effectively eliminated the occurrence of Miller open when depletion-mode GaN devices were used in high-voltage applications. The circuit was designed and simulated in a 035 μm BCD process. The results showed that the circuit could output stably a negative voltage of -14 V in a wide input range, the operating efficiency could reach 80%~87% under 20~130 mA constant load current. The output voltage of GaN device kept stable during gate switches switching at 05~1 MHz operating frequency. This circuit met the needs of high voltage applications.