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UCD3138A： Dpwm confugure。

Ford.Fang
Prodigy 90 points
Part Number: UCD3138A
Other Parts Discussed in Thread: UCD3138

Hi,Ti‘s Engineer。I would like to ask some questions about the use of UCD3138。

In the triangle mode, can the value of DPWM B Rising Edge exceed the center point (Period/2)?

For example: Period=16000, Filter Duty=200, Cycle Adjust A=200, Cycle Adjust B=200

Dpwm1Regs.DPWMCTRL0.bit.D_ENABLE = 0;

Dpwm1Regs.DPWMCTRL0.bit.PWM_B_INV = 0;

Calculated at this time: DPWM B Rising Edge = 8100, DPWM B Falling Edge = 7900

Does the duty cycle of DPWM output become 98.75%? At this time, DPWM B Rising Edge will exceed the center point of 8000.

If DPWM B Rising Edge cannot exceed the midpoint, is the dead time squeezed out, and the final output is 0%?

  • 0
    TI__Expert 6575 points

    Hi,

    In triangular mode the DPWM B Rising edge can not exceed Period/2.

    I think in the scenario described above, the dead time will be squeezed out and the final output will be 0%.

    The expert on Triangular mode on UCD3138 is out of the office till December 1st, 2020, and he will be able to review my reply and follow up on this question at that time.

    Regards,

    Swami

  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 90 points

    Thank you for the reply!

    I hope that the subsequent experts can further confirm my problem, because this has a great impact on the reliability of our product design.

  • 0 in reply to Ford.Fang
    TI__Expert 7310 points

    Hello Ford,

    In your example, the rising edge = 8100, the falling edge = 8300, the DPWM pulse width is still 200, the duty is 1.25%.

    Regards,

    Bosheng

  • 0 in reply to Bosheng Sun
    Prodigy 90 points

    Sorry, I missed one symbol for the value above.

    Cycle Adjust B= -200, DPWM B Rising Edge = 8100, DPWM B Falling Edge = 7900

    How is the duty cycle output at this time?

    Say sorry again, it added a lot of trouble to you.

  • 0 in reply to Ford.Fang
    TI__Expert 7310 points

    Hi Ford, in this case, the duty will be 98.75%. 

  • 0 in reply to Bosheng Sun
    Prodigy 90 points

    Thanks for your reply！

    As mentioned above, I did an experimental test today, the actual output of the duty cycle is 0%, and it will not output 98.75%.

    At the same time, I found a problem. In the calculation of the edge in the triangle mode in the technical manual, the filter is only provided as an output to the DPWM to calculate the duty cycle, but if the dead time is configured, when the above example occurs, The output value of the filter (FilterYnread) is always greater than the dead time. Theoretically, the DPWM dead zone as a later stage should not affect the output of the Filter. I think this may be why, the actual output value in the above routine is 0% instead of 98.75%.

    I hope you can verify it for me, because the duty cycle actually tested here is indeed 0%。

  • 0 in reply to Ford.Fang
    TI__Expert 7310 points

    Hi Ford, I just verified that the duty is 0, you are correct. We have never run triangle mode like this way. What do you mean deadtime? triangle mode only works for DPWMB, DPWMA is always off. 

    Regards,

    Bosheng

  • 0 in reply to Bosheng Sun
    Prodigy 90 points

    Thank you for helping me verify!

    I haven’t gone to work on vacation these days, so I can’t reply to your message in time.

    I am in the power supply industry, and for some reasons I chose to use the triangle mode. At the same time, the dead time I mentioned corresponds to Cycle Adjust A and Cycle Adjust B in the triangle mode.

    My English is not very good. Please forgive me if I say something wrong.

    Regards,

    Ford

  • 0 in reply to Ford.Fang
    TI__Expert 7310 points

    Hi Ford, no problem, I am going to close this thread.

    Regards,

    Bosheng