In a standard bootstrap setup, the high‑side driver is powered by a bootstrap capacitor (CBOOT) and diode (DBOOT). When the high‑side switch turns off, the switch node is pulled low. The switch node’s voltage is limited to approximately 1 V below ground by the silicon FET’s body diode.
In contrast, GaN FETs do not have a silicon body diode. Instead, when they conduct in reverse, they behave like body diode( –2 V to –3 V). This more negative switch‑node voltage adds onto the bootstrap capacitor voltage, which can overcharge the high‑side gate drive. This risks:
- Excessive gate‑source voltage
- Possible damage to the GaN device
- Incorrect or unstable gate drive operation
To avoid this, use of a smart switch can prevent the driver from overcharging without the need for extra clamping diodes. This active switch turns on after the BOT gate is on, resulting in a regulated high-side gate drive voltage that does not depend on the body diode drop. In the case of extended dead times, these controllers tolerate negative spikes on the switch node.
DC DC Switching Controllers | Power Management (PMIC) |DigiKey
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