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LAUNCHXL-F280039C: C2000 ePWM SW force A and B to both low even in complementary Dead Band

ahugron hugron
Intellectual 320 points
Part Number: LAUNCHXL-F280039C

Hi,

It seems that when configured ePWMs in complementary mode or using dead band, when I try to SW force A and B to low, B stays high. I suppose that this is a fact that they are complementary. But in my condition, when I need ePWM to be OFF or during a burst mode, I need both A and B to be low.

How can we achieve that with Dead band activated?

Thanks,


Arnaud

  • 0
    TI__Genius 9031 points

    Hello,

    The answer to this will depend on DB configuration, as well as how you're performing the SW force.

    1. Is ePWMB generated from the AQ, or is it derived from ePWMA?
    2. Are either ePWMA/B inverted using the DB?
    3. Are you utilizing the AQ SW Force functionality, or are you using a trip?

    Alternatively, instead of independently answering each question, a screenshot of the values in the relevant ePWM configuration registers in CCS debug would also work!

    Regards,
    Jason Osborn

  • 0 in reply to Jason Osborn
    Intellectual 320 points

    Hi,

    1. The ePWMB is generated by dead band Active High complementary based on ePWMA.

    2. Yes, B is inverted using DB

    3. So far, I am testing with AQ Continuous SW Force Action. But I will also need with TRIP. In other need for both cases.

    Just using a complementary active high PWM will do. Let me know if you need the code.

    Thanks,


    Arnaud

  • 0 in reply to ahugron hugron
    TI__Genius 9031 points

    Hello,

    Thanks for getting back to me! I'm going to explain what's going on, and also provide a direct solution to your problem, which will be in bold.

    Essentially, what's important to know here is that ePWMB does not care what's going on in the AQ. You can do whatever you want in the AQ to ePWMB- because of the DB settings, ePWMB only cares about the current state of ePWMA. Take a look at Figure 20-21 in the Device TRM for an explanation of signal flow in the ePWM, with the AQ highlighted.

    For that reason, to implement the functionality you're looking for, you're going to want to implement a OST, or One-Shot Trip, in the TZ. This will be able to independently affect the value of each after the DB. The AQ can't do what you're looking for because you're overriding the ePWMB AQ output in the DB.

    The TZFRC register allows you to implement a forced trip event, similar to AQ SW Force.

    Regards,
    Jason Osborn

  • 0 in reply to Jason Osborn
    Intellectual 320 points

    Hi,

    Seems to be ok (as expected), but when I clear OST flag by using EPWM_ClearTripZoneFlag for OST (restart PWMs), it seems that ePWM restart at random count.

    The issue is that I have also 3 ePWMs (PHSEN at 60 degree) .

    Is there a better way to start at zero and for 3 phase. ePWM.

    Thanks,


    Arnaud

  • 0 in reply to ahugron hugron
    TI__Genius 9031 points

    Hello,

    Think of an OST as a mask. When you slide it in place over the ePWM you only see the output that the OST set, but behind the mask, the ePWM is still running as normal. OST does not pause the ePWM, and clearing the OST flag does not restart the ePWM.

    To reset the ePWM timer, you'll need a sync-in signal. See the TRM section 20.4.3.3 for more details on the sync process.

    Regards,
    Jason Osborn

    (As an aside, it may be worthwhile to look into CBC, or Cycle-By-Cycle, trips, depending on what your use-case is. They do not require manual reset, and their reset is aligned with a pre-defined choice of events-> CTR=PRD or CTR=ZRO)