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TMS320F28335 EPWM6 problem

Georgios Lempidis
Prodigy 100 points

Hi to all

I use the ePWM 4,5 and 6 in order to generate the PWM signal for an 3ph Interleaved DC-DC Converter.I use up-down count mode and the channels have 120 degrees phase shift from each other.

The ePWM 4 and 5 work perfect but in ePWM6 if i increase the COMPA value more than the 65% of the TBPRD value i get a constant on in the output pin(off for the complimentary pin). This mean that i can have a minimum duty cycle of 35%

I have verified the values with the JTAG in the watch window and with CAN. Also the exact same code works perfectly if i use the ePWM 1,2 and 3 but the application need to use the 4,5 and 6.

I would appreciate if someone could help in this

Thank you in advance

  • 0
    TI__Guru 57255 points

    Georgios,

    If the same code works with PWM1-3, it should work on 4-6.  There isn't any real difference that I'm aware of.

    Giving us some information on the PWM setup (particularly up-count vs up-down count and how you've done phase synchronization) may help us.  However, from personal experience I'd recommend doing a quick search through your code for anything that may inadvertently be touching PWM6. 


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Prodigy 100 points

    Thanks for the responece

    I have 3749 PRD value. Everithis is sycnhornised with the Zero of the PWM4 and the the PWM5 has a phase *** in the shift register of 2499 stemps and the pwm 6 has a phase shift of 4998 steps.

    the PWM 6  works with COMPA up to 2499 steps.in 2500 steps is not working any more. 

    Now that i made converter anerithing in steps (in the software i have the 2/3 and 4/3 of the PRD )everithig in steps i realises that the piont that is not working is the same . as tha phase shift for 120 degrees. i will check if this effect the software and i will update it today.

    Thank you 

     

  • 0 in reply to Georgios Lempidis
    Prodigy 100 points

    The problem solved by changing the synchronization settings. Instead to synchronize all channels with the PWM4 and then use the Phase register to give to the PWM5 120° and to PWM6 240° I used sequential synchronization and in both PWM5 and PWM6i give a phase of 120°.

      THE QUESTION REMAINS!!! Why is the same code working perfect with channels 1, 2, 3 and in channels 4,5,6 is not working. I checked in the datasheet and in errata and i found no mention of a limitation to PWM6. The synchronization scheme i found from 4 day Workshop for 28335 i attended in Landshut a couple of years ago.

  • 0 in reply to Georgios Lempidis
    TI__Guru 57255 points

    Georgios,

    I'm glad that you were able to solve your problem. 

    However, I am puzzled with why PWM6 does not synchronize with the previous code.  As I mentioned previously, there is no known difference with PWM6.  I've also been able to synchronize PWM6 in previous projects.

    If you can send your PWM configuration (you can either attach it here or friend me on E2E & then send it via private message) from the older software, I'll take a look when I'm able.


    Thank you,
    Brett