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I have selected an SiC MOSFET (UJ3C120040K3S) for my pulsed power application. My rise and fall time requirements are both 20 nS. My gate drive voltage will be 15 V. Based on the total gate charge value of 51 nF provided in the datasheet, I calculated the gate capacitance to be 3.4 nF (Cg = Qg/Vg).

In order to calculate the drive strength I calculated the gate current as follows: Ig = Qg/tr which was equal to 5.8A. Based on this gate current, I selected a this driver. In table 2 of the driver datasheet the rise time and fall time values are 4 nS typical for a Cload of 1.8 nF. I have a couple of questions.

  1. My gate capacitance is 3.4 nF whereas the Cload is 1.8 nF. How do I scale this value to find out the exact rise and fall times?
  2. Should the rise and fall times of the driver be more or less than that of the MOSFET?
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  • \$\begingroup\$ Rise/fall is gate, or drain? Remember output transition times are faster. \$\endgroup\$
    – Tim Williams
    Commented Oct 17, 2023 at 1:16
  • \$\begingroup\$ I basically want to know how to calculate the rise and fall times of the gate driver based on the input capacitance of the MOSFET. This is because, the CLoad for the gate driver is not the same as the Cin of the MOSFET. \$\endgroup\$
    – power_electronics_engineer
    Commented Oct 17, 2023 at 5:18
  • \$\begingroup\$ Please link the data sheet. \$\endgroup\$
    – Andy aka
    Commented Oct 17, 2023 at 7:52
  • \$\begingroup\$ @Andyaka, Here is the datasheet of the MOSFET link \$\endgroup\$
    – power_electronics_engineer
    Commented Oct 17, 2023 at 16:22
  • \$\begingroup\$ I tried calculating the rise time as follows: Gate Driver Datasheet: tr = 4 nS @test condition - CLoad = 1.8 nF and VDD = 12V. The gate current can be calculated using the following formula. Ig = Qg/tr where Qg = CLoad * VDD. Ig = (CLoad * VDD) / tr Ig = 5.4 A. My test conditions are as follows: Ctest = 3.4 nF and VDD = 15 V. Calculating Qg from test conditions: Qg = Ctest * VDD Qg = 3.4 nF * 15 V = 51 nC Calculate the gate current (Ig): Ig = Qg / tr tr = Qg / Ig Now, plug in the values: tr = 51 nC / 5.4 A tr = 9.45 ns Is this calculation sound? \$\endgroup\$
    – power_electronics_engineer
    Commented Oct 17, 2023 at 17:33

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