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UCC28950 datasheet page 59 equation 169

Bharath Manogna
Prodigy 60 points

The calculation mentions the mmag = 400*47/(2.76e-03*100) = 7mV/us but should it be 68mV/us?

  • 0
    TI__Mastermind 31580 points
    Hi Bharath,

    The apps engineer for this product will be back in the office on Monday and I will ask him to review the calculations.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Mastermind 25570 points
    Hello Bharath

    Yes, you are correct. We made a mistake and dropped a factor of ten when drawing up the datasheet and the correct slope provided by the magnetizing current is indeed 68mV/us. This means that the magnetizing current actually provides most of the slope compensation needed and the value of RSUM should be re-calculated. However, a word of caution here - the magnetizing current slope is calculated at 400V in this example. At minimum input voltage - let's say around 260V - where the duty cycle is greatest and the amount of slope compensation needed is also greatest the magnetizing current will provide significantly less slope compensation. We didn't worry about that in the DS example because, although the variation in the slope of the magnetizing current is present, it was very small in relation to the total slope compensation ramp needed and we didn't worry about it.

    I've made a note to correct this in an upcoming version of the DS -

    Thanks for bringing this to our attention.

    Regards
    Colin