Switch Bootstrap Charging Circuit Suitable for Gate Drive Circuit of GaN Power Device

A switch bootstrap charging circuit suitable for a gate drive circuit of a GaN power device, wherein, the GaN power device comprises an upper power transistor and a lower power transistor, the switch bootstrap charging circuit comprising:

• a low-voltage MOSFET, a high-voltage MOSFET, a bootstrap capacitor, a high-voltage MOSFET control module, and a low-voltage MOSFET control module, wherein the low-voltage MOSFET is a PMOS transistor, and the high-voltage MOSFET is a high-voltage PMOS transistor;
• a source of the low-voltage MOSFET is connected to a power supply voltage, a drain of the low-voltage MOSFET is connected to a drain of the high-voltage MOSFET, and a gate of the low-voltage MOSFET is connected to a gate drive signal of the low-voltage MOSFET;
• a gate of the high-voltage MOSFET is connected to a gate drive signal of the high-voltage MOSFET, a source of the high-voltage MOSFET is connected to an upper electrode plate of the bootstrap capacitor, and the source of the high-voltage MOSFET serves as an output terminal of the switch bootstrap charging circuit;
• a lower electrode plate of the bootstrap capacitor is connected to a switch node of the gate drive circuit of the GaN power devices;
• the low-voltage MOSFET control module is enabled by an enable signal to generate the gate drive signal of the low-voltage MOSFET under a control of a first low-side control signal;
• the gate drive signal of the low-voltage MOSFET and the first low-side control signal are at reverse logic levels;
• the first low-side control signal and a gate drive signal of the lower power transistor are at a first same logic level;
• the enable signal and the first undervoltage signal are at a second same logic level;
• and the first undervoltage signal is an undervoltage signal of the power supply voltage;
• the high-voltage MOSFET control module comprises a zero-voltage sensing module, a high-voltage switching logic control module, and a high-voltage level-shift module;
• the zero-voltage sensing module is enabled by the enable signal, and the zero-voltage sensing module samples a signal at a switch node of the gate drive circuit of the GaN power devices under a control of a second low-side control signal and generates a zero-voltage sensing signal;
• if the signal at the switch node of the gate drive circuit of the GaN power devices has a high voltage, the zero-voltage sensing signal is at a first low level;
• if the signal at the switch node of the gate drive circuit of the GaN power devices is essentially zero, the zero-voltage sensing signal is at a high level;
• the second low-side control signal and the gate drive signal of the lower power transistor are at a third same logic level, and the second low-side control signal is obtained by delaying the first low-side control signal;
• the high-voltage switching logic control module is enabled by the enable signal for generating a determination signal according to the zero-voltage sensing signal and the first low-side control signal;
• the high-voltage level-shift module is configured to shift a power rail of the determination signal from power supply voltage to ground to output terminal signal of the switch bootstrap charging circuit to the signal at the switch node;
• the high-voltage switching logic control module generates the gate drive signal of the high-voltage MOSFET according to the determination signal processed by the high-voltage level-shift module and the second undervoltage signal;
• the gate drive signal of the high-voltage MOSFET is at a second low level only when the second undervoltage signal, the first low-side control signal, and the zero-voltage sensing signal are all at the high level;
• otherwise, the gate drive signal of the high-voltage MOSFET is at the high level;
• and
• the second undervoltage signal is an undervoltage signal between the output terminal of the switch bootstrap charging circuit and the switch node.