This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC23513: High dv/dt causes SiC MOSFET to turn on incorrectly

Part Number: UCC23513
Other Parts Discussed in Thread: UCC23514

Tool/software:

Hi team,

 my customer using the UCC23513 with SIC fet of IMZA120R040M1H, we found the Vds of the lower FET will increase. At this time, the charge is transferred to the gate of the lower FET through the Miller capacitor Cgd, causing a small spike in the gate voltage.

 In this case, do we have some solution to help UCC23513 close this issue here?

  • Hi Allen,

    The voltage spike is proportional to both the injected Miller current (I=C d(Vds)/dt) and the impedance between the gate and source (Lgate +Rgate+Rol+Rg). You should try to reduce both of these.

    One trick to reduce the dV/dt across the low-side switch is to add a little distance between the phase and the low-side drain. This will add a tiny amount of inductance, which will absorb some of the dV/dt from the high-side closing, and divide down the dV/dt across the Miller Cdg. Another possibility is to add a snubber to the High Voltage rail. This can be tuned to cause a high frequency transient droop when the switch turns on, which will lower the dV/dt a small amount also.

    On the gate driver side, I do not see the UCC23513 in your schematic. Based on your labels, I surmise that you have 39 ohms of turn-off resistance. Also, you have 2.2 ohms in series with your external Cgs. This is a lot of resistance.

    If you have a ground plane, you likely have very low turn-off ringing. You can probably use 1-2 ohms of turn-off resistance and not generate significant undershoot. For R102 and R100, You should probably use 0 ohms, since these resistors prevent the capacitors from instantaneously absorbing the miller injection, and integrating the current down to a lower voltage.

    There is a version of this device called the UCC23514, which has a Miller clamp pin added. This lets you use large turn off resistors, and then the 0 ohm Miller clamp pin closes in parallel with these resistors to provide a low impedance bypass for the injected Miller current.

    One other possibility is if you do not need 55A in this application, you can use a cheaper FET with higher Rdson and lower Cgd. The larger, more expensive FETs have higher capacitance and have more Miller injection than right-sized FETs.

    Best regards,

    Sean