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UCC27282: Loss calculation

Paul Miller11
Prodigy 245 points

Part Number: UCC27282

I'm trying to figure out how to estimate the dynamic losses in a UCC27282 circuit and select gate driving components.  Section 8.2.2.2 and 8.2.2.3 look like they are just what I need...but I'm not clear on how to find / derive the internal driver resistances need to complete these calculations - Rgd_r , Rhoh, Rhol, Rloh, Rlol.  The TechNote referenced in the datasheet also bases its calculations on these parameters.

How do I figure out what numbers to use?

Thanks,

  • 0
    TI__Prodigy 376 points

    Hi Paul Miller,

    Thank you for asking this question. Some of the datasheets will say in the 6.5 Electrical Characteristics table what the internal driver resistances are, its inconsistent whether this is included or not. For this particular datasheet it is assumed the value will be calculated from the information in the table. In section 8.2.2.2 in equation 6 it describes RGD_R as the average value of pullup and pulldown resistor. This will be dependent on whether it is the high-side or low-side output. In section 8.2.2.3 in equations 9, 10, 11, and 12 it describes the following values which I will calculate based on the typical values described in section 6.5:

    • RHOH is the high-side pullup resistor, RHOH = VHOH / IHO = 130mV / 100mA = 1.3Ω
    • RHOL is the high-side pullup resistor, RHOL = VHOL / IHO = 100mV / 100mA = 1Ω
    • RLOH is the high-side pullup resistor, RLOH = VLOH / ILO = 130mV / 100mA = 1.3Ω
    • RLOL is the high-side pullup resistor, RLOL = VLOL / ILO = 85mV / 100mA = 0.85Ω

    So then for the high-side RGD_R is 1.15Ω and for the low-side RGD_R is 1.075Ω. In the case of max it recommends to use 4Ω for RGD_R. You should be able to calculate equation 6 from there to find your dynamic losses.

    The datasheets can be inconsistent on what information they provide and what formulas they suggest using, and the technical notes can be a little scattered and use different terminology than the datasheet. If you have any more questions feel free to ask.

    Regards,

    Carson Gamble