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LM5113-Slide3

With the many benefits of eGaN FET technology, there are a few design challenges. The low charge and low voltage gate drive reduce gate losses. In designing it is a must to consider the low threshold voltage. The knee of the transfer characteristics curve is where the gate to source voltage is during the switching action. Typically, for numerous reasons, turn on tends to be slowed with a series gate resistor. For reduced power dissipation and dv/dt immunity, it is generally desirable to turn off quickly. Historically, this was accomplished with a diode to bypass the series gate resistor. With a low threshold device, there is low potential across the series of gate resistance, reducing gate current. Further reduction of voltage in a diode or inductance common to the power and drive paths would significantly degrade performance. Therefore, a bypass diode cannot be used, and driver sink resistance becomes more critical. Furthermore, power loop di/dt in the source inductance that is common to the power and drive paths induces a voltage that is subtracted from the turn off potential.

PTM Published on: 2012-10-16