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UCD3138 MIN_DUTY_MODE = 1 does not work

hakan aydin
Intellectual 470 points
Other Parts Discussed in Thread: UCD3138

We are working with the UCD3138 LLC EVM and its source code. In init_dpwms.c, all the PWMs have their min duty mode set to "2":

Dpwm0Regs.DPWMCTRL0.bit.MIN_DUTY_MODE = 2;

What this does is that, when the duty cycle goes under a threshold, it is kept just at that threshold.

However, for our supply, this will not work as well, so we would rather work in mode "1", which says, when the duty cycle goes under a threshold, the duty is forced down to "0".

However, when we build the firmware with that setting, when we go under the duty threshold, the IC is outputting HIGH from the PWM pin, instead of "0".

Any ideas what might be wrong?

  • 0
    Intellectual 470 points

    Any help?

    OFF-TOPIC QUESTION:   Is there any way to get support for the UCD31XX series outside of these support forums? It is very frustrating that this is the only support channel and slows us down to a crawl. (paid support from an expert is also on the table).

  • 0 in reply to hakan aydin
    Expert 2600 points

    Hi,

    run into the same Problem. Didn't see that Output is high, just see, there is no *** anymore, doesnt matter if the filter Output is below or above the threshold. Switch Min_DUTY_MODE = 1 and DPWM stops.

    Also tried 'Light Load' module, doesnt work ....

    Support here is very slow, yes- It  is a shame for a Company as TI is (or will be).

    With best regards

    Gerhard

  • 0 in reply to Gerhard Kreuzer
    Expert 2600 points

    Hi,

    maybe I found a reason.

    First I give up but after playing around I set my converter to a operating Point and suddenly the min duty mode works.

    But here the whole strory:

    It was just luck to find an operating Point, where the mode works. Not very stable but .. To find out more I tried to use MIN_DUTY_MODE = 2, and now I get quite wide pulses ??? I expected small pulses, as the Content of the DPWMMINDUTYLOW Register determinds the polse width in this mode. Ahhhh.

    So I used the Memory Debugger and reduced the value of this Register until I get the smallest possible pulse. I also adusted the DPWMMINDUTYHI to this value with a very small threshold and ... works.

    My converter has smooth transitions between hiccup mode and normal mode, Output voltage is ok, no Problems any longer.

    I set the new values into relation to the old values and ==> / 16. Oh my god, just a scaling Problem.

    Fazit: The DPWMMINDUTYLOW and DPWMMINDUTYHI Registers Need scaled values. If your filter Output delivers values around 5000 at the border Hiccup mode- normal mode, than use about 320 and 322, set MIN_DUTY_MODE=1 and ist done.

    Hope this helps you also.

    My additional Problem was, that I use gate transformers and the Output of the DPWM delivers just junk if the values wern't set correct, so you see a H at the Output but I see strange Levels cause my gate transformer saturates and the current Limit of the Driver shut the Driver down, and I end up with totally messed up signals.

    With best regards

    Gerhard

  • 0 in reply to Gerhard Kreuzer
    TI__Expert 4970 points

    Hakan / Gerhard,

    This is a very interesting question. I have brought it to the attention of one of our other systems engineers who will work in the lab to understand this more. I will get back to you soon. Thanks!

    Regards,

    Brandon Vonk

  • 0 in reply to Brandon Vonk
    Expert 2600 points

    Hi Brandon,

    thanks for the Response.

    I will be out from tomorrow to saturday (electronica 2014 @ Munich), but can probably check my mails. If you Need detatils, you have to wait to next week, sorry.

    With best regards

    Gerhard