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TMS320F28379D: PWM synchronization signals

Aditya Ghule1
Intellectual 450 points

Part Number: TMS320F28379D

Hi,

I am trying to synchronize the TBCTR for multiple PWMs.  I was able to get the system working for ePWM1 and ePWM2 where ePWM1:SYNCOSEL  = 0  and  ePWM2:SYNCOSEL  = 2.  I want to setup a similar synchronization with ePWM5 and ePWM6.  The synchronization works properly when the SYNCOSEL on both 5 and 6 is 0 and PHSEN is 1.  But does not work with ePWM5:SYNCOSEL  = 0  and  ePWM6:SYNCOSEL  = 2 . I was curious if it is not possible to have two PWM channels providing separate synchronization signals  ( syncosel = 1 or 2).  

Thank you,

Aditya

  • 0
    TI__Mastermind 26340 points

    Hi Aditya,

    Can you please describe what your SYNCOSEL for epwm 4 is as well as EPWM4SYNCIN, are they just set to the default?

    What is your complete sync chain? 

    Aditya Ghule1 said:
    But does not work with ePWM5:SYNCOSEL  = 0  and  ePWM6:SYNCOSEL  = 2

    SYNCOSEL simply determines what would be the Sync pulse coming out of the module. Are you seeing that epwm6 is no longer in sync with epwm5?

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    Intellectual 450 points

    Hi Marlyn,

    The SYNCOSEL for epwm4 (and all others which I am not using) is just set to default (0).

    I also realized I made a mistake above.  The system works when But does not work with ePWM5:SYNCOSEL  = 2(or1)  and  ePWM6:SYNCOSEL  = 0.  When I select this I see approximately a 2 EPWM cycle ( 20ns) delay between the signals.

    The complete sync chain that I am trying to implement is ePWM2 synchronized with ePWM1 and ePWM6 synchronized with ePWM5.

    Thank you,

    Aditya

  • 0 in reply to Aditya Ghule1
    TI__Mastermind 26340 points

    Hi Aditya,

    Are you using high resolution period mode? Note that we have comments in the Technical Reference Manual that address the synchronization SYNCOSEL options when in this mode.

    Aditya Ghule1 said:
    When I select this I see approximately a 2 EPWM cycle ( 20ns) delay between the signals.

    Do you get the same results for both SYNCOSEL 2 and 1? What phase value are you setting for ePWM6?

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    Intellectual 450 points

    Hi Marlyn,

    I am using phase value of 1 as I need the PWMs to be synchronized exactly.  I went through the documentation for SYNCOSEL options in the Technical Reference Manual, so I am guessing using the ePWM 1 to synchronize all PWMs would be an option.  However I was not able to find information about operating two PWMs on independant time counters with their own sync signal.

    Thanks,

    Aditya

  • 0 in reply to Aditya Ghule1
    TI__Mastermind 26340 points

    Hi Aditya,

    Do you have any configuration differences between epwm 1/2 and epwm 5/6?

    Also, do you get the same results for both SYNCOSEL 2 and 1?

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    Intellectual 450 points

    Hi Marlyn,

    The TBCTL configuration for 1/2 and 5/6 is the same (except the syncosel = 1) for pwm 1 and 0 for others. I had to make a few changes to how the PWM was used and so the SYNCOSEL =2 cannot be used due to a varying CMPB so I could only test the case for SYNCOSEL =1. I forgot mention before that I am not using the high resolution mode.

    Thanks,
    Aditya

  • 0 in reply to Aditya Ghule1
    TI__Mastermind 26340 points

    Hi Aditya,

    Thank you for providing the information. I tested it on my side and I do not see any issues with trying to synchronize epwm2 to epwm1 and epwm5 to epwm6 when SYNCOSEL=1.

    Would you please check your clock prescalers?

    Below is the setting that I have. If you are not using a divider then you may need to increase your phase value. 

        EPWM_setClockPrescaler(base,
                           EPWM_CLOCK_DIVIDER_8,
                           EPWM_HSCLOCK_DIVIDER_1);

    Also, keep in mind that if you are using up-down count then you will have to take this into account as well.

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    Intellectual 450 points

    Hi Marlyn,

    Thanks a lot for the help.  I realized that I had not properly configured TBPHS register.   I am using a lower clock divider, I am not sure if that was making the problem worse.  Setting the correct TBPHS according to 15.4.3.3 to account for the delay between the channels solved the issue and I am able to independently configure the two sets of PWM.  

    Thanks again for all the help,

    Aditya