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UCC21750-Q1: question about CMTI

Yuan Tan63
Expert 3280 points
Part Number: UCC21750-Q1

hi,

here are some CMTI questions want to confirm:

1 is CMTI only for isolated driver?

I supposed it's also important for half bridge driver since the upper mos's ground is floating with common voltage changing. but I don't found "CMTI" in their datasheet. 

2 how to estimate the CMTI?

I know the CMTI should be common voltage/transition time. common voltage usually is bus voltage but what's the estimated as transition time? can we calculated as the rising time of IGBT/MOS?

thanks,

B&R

Yuan

  • 0
    TI__Expert 3860 points

    Hi Yuan, 

    1. I believe CMTI is defined as "the maximum tolerable rate of rise or fall of the common mode voltage applied between two isolated circuits" as mentioned in this application note. Therefore, this parameter is also defined for our isolated gate drivers. Let me reach out to my colleague on the non-isolated drivers team about this and I'll get back to you. 

    2. Yes, you can calculate your common mode transient voltage by doing bus voltage/ rise time of the transistor. 

    Thanks, 

    Vivian

  • 0
    TI__Expert 3860 points

    Hi Yuan, 

    This is what my non-isolated driver colleague said - 

    "In a lot of ways there is a similar concern, CMTI in effect is a dV/dt event on the driver output relative to the input (control) and ground. The limitation or difference on the non iso drivers is that the driver ground reference, HS on the floating high side driver, has a definite limitation on the negative voltage capability relative to ground."

    Hope this answers your question! 

    Thanks, 

    Vivian