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UCD3138 complementary DPWM outputs with SYNChronization

ziopaper
Intellectual 940 points

Hello,

is there a way to guarantee non-overlapping DPWM signals on a synchronized DPWM module?

DPWM module setup up in MULTI mode. When not-synchronized, I have Kcomp setup up as multiplier to guarantee EVENT4 never goes past the PWM period, and this way I never have shoot-through.

When I synchronize with an external signal, I am unable to guarantee this. IF the frequency of the SYNC signal is known, I can obviously setup KCOMP such that I will never have overlapping DPWMs, but in case the ext frequency is different from what I had expected, I get shoot-through.

Is there a setting that will NOT allow DPWMA and DPWMB to overlap, regardless of external SYNC signal?

Thank you

  • 0
    TI__Genius 17090 points
    There is a simple technique if you're in normal mode, but there is no easy way to handle it in normal mode. You can handle a deviation in frequency by moving Event 4 in from the end of the period, but you have to guarantee that the sync pulse will never start when DPWMB is on.
    If you really want to do dynamic sync without missing any pulses, you can use the 24 bit timer capture pin to measure both phase and frequency of the signal you are syncing to, almost match the frequency, and wait for the phase to match, and then enable sync. And then match the frequency more precisely. If you are willing to skip a pulse or two, you can disable the output, enable the sync, and then after a couple of phases, reenable the output. If you're doing it at start up, you just have to match the frequency and enable the sync before turning things on.
  • 0 in reply to Ian Bower
    Intellectual 940 points
    thank you Ian. I thought about something like what you described.
    So the PWM module itself cannot guarantee that will not have A and B outputs on at the same time? (even at the cost of losing synchronization) Am I right?

    thanks
  • 0 in reply to ziopaper
    TI__Genius 17090 points
    Yes, that is correct. Sometimes people have used dual gate drivers with shoot-through protection.