Active Miller clamp feature is important to prevent the false turn-on while the driver is in OFF state. In applications which the device can be in synchronous rectifier mode, the body diode conducts the current during the deadtime while the device is in OFF state, the drain-source or collector-emitter voltage remains the same and the dV/dt happens when the other power semiconductor of the phase leg turns on. The low internal pull-down impedance of UCC21755-Q1 can provide a strong pulldown to hold the OUTL to VEE. However, external gate resistance is usually adopted to limit the dV/dt. The Miller effect during the turn on transient of the other power semiconductor can cause a voltage drop on the external gate resistor, which boost the gate-source or gate-emitter voltage. If the voltage on V_GS or V_GE is higher than the threshold voltage of the power semiconductor, a shoot through can happen and cause catastrophic damage. The active Miller clamp feature of UCC21755-Q1 drives an internal MOSFET, which connects to the device gate. The MOSFET is triggered when the gate voltage is lower than V_CLMPTH, which is 2 V above VEE, and creates a low impedance path to avoid the false turn on issue.

Figure 7-4 Active Miller Clamp