R and C values for a bldc card

Discussion in 'The Projects Forum' started by jm-a, Feb 28, 2011.

  1. jm-a

    Thread Starter Active Member

    Oct 20, 2010
    Hi all,

    Last answer, - I hope - before etching and drilling the board.

    In fact after reading, MC33035 , MC33039 datasheet and AN1046 , I don't know why these resistors and capacitors have been added.

    If someone could explain the way to compute ,and their purpose of course, would be great.

    It's really the scheme -see for this question left middle area -
    of my true burnt card, due to bad cooling - no fan and box enclosed - and also manufacturing....

    I only want to know use and maths about R1 -> R6 and C1 - > C6.

    See ( RC-MC33035-33039.png )

    Thanks a lot.

  2. wayneh


    Sep 9, 2010
    Your questions are unclear, but here goes.

    R1-R6 are used to pull up the voltage on those lines. I would assume that the signal, when present, pulls the voltage down. So the size of those resistors depends on the specs of the device sending the signal.

    The capacitors work as low-pass filters, and will pass high frequency spikes or noise to ground, to quiet the signal. The size of these depends on the highest frequency the system needs to respond to. I mean, if they are too large then only low frequencies will pass and even a desired signal might get filtered out. There's probably a wide gap between "enough" filtering and "too much" filtering, so the exact size of these caps may be somewhat arbitrary.