Devices based on III/V semiconductors such as Gallium Nitride, GaN, diodes and GaN N-channel transistors, have a number of advantageous properties. For instance, GaN transistors have a relatively low on-resistance and can achieve higher switching speed compared to their silicon-based counterpart. As such, GaN components are well suited for the design of switching converters and high-voltage power circuits.
However, GaN devices such as enhancement or depletion mode high-electron-mobility transistor E-HEMT and D-HEMT, require an accurate gate voltage in order to fully turn on with a low on-resistance (Rds_on) value. A typical voltage gate value may in the order of 6V, however the gate voltage may vary from device to device depending on the manufacturing process. Driving a GaN transistor with a higher gate voltage can cause severe degradation and over-stress to the GaN transistor, hence shortening the life-time of the device. In contrast, driving a GaN transistor with a lower gate voltage can limit the Rds_on performance; for instance, the drain to source voltage may greatly increase.
Switching converters and other electronic circuits comprising a half-bridge topology in which a high side power switch is coupled to a low side power switch via a switching node: the gate voltage of the high-side power switch is provided by a high side driver. The high-side driver is powered by a capacitor often referred to as boot capacitor. Current circuits do not allow a precise and reliable control of the voltage across the boot capacitor, hence limiting their use with GaN transistors.