JAJSIW1A March 2020 – January 2024 UCC21739-Q1
PRODUCTION DATA
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 UCC21739-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 VGS or VGE 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 UCC21739-Q1 drives an external MOSFET, which connects to the device gate. The external MOSFET is triggered when the gate voltage is lower than VCLMPTH, which is 2V above VEE, and creates a low impedance path to avoid the false turn on issue.