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TMS320F280049C: Hrpwm: question of duty cycle adjustment in up-down mode

Green Deng
Expert 4490 points
Part Number: TMS320F280049C

Dear team:

Routine: hrpwm_ex4_duty_updown_sfo.c

SFO enabled

My customer wants to generate centrosymmetric hrpwm waveform in up-down mode. How to adjust the duty cycle in high-resolution mode? The customer tried the following ways:

(1) In "both edge" mode, CMPAHR will phase shift the waveform instead of changing the duty cycle

(2) In "falling edge" mode, there is high-resolution duty cycle adjustment, but it cannot represent all duty cycles

Is there any better way?

Best regards

  • 0
    TI__Guru 52010 points
    Green Deng said:
    (1) In "both edge" mode, CMPAHR will phase shift the waveform instead of changing the duty cycle

    This should not shift both edges in the same direction. It will shift the two edges towards/away from each other causing change in duty cycle only.

  • 0 in reply to Nima Eskandari
    TI__Expert 4490 points

    Hi Nima:

    My customer tested it and found that the duty cycle can be modified with high accuracy in the asymmetric mode. But in symmetric mode, the two edges will move in the same direction.

  • 0 in reply to Green Deng
    TI__Guru 52010 points

    What is the action qualifier settings your customer is using?

  • 0 in reply to Nima Eskandari
    TI__Expert 4490 points

    Hi Nima:

    This is the action qualifier settings:

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    EPWM_setActionQualifierAction(ePWM[j],EPWM_AQ_OUTPUT_A,EPWM_AQ_OUTPUT_HIGH,EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(ePWM[j],EPWM_AQ_OUTPUT_A,EPWM_AQ_OUTPUT_LOW,EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    HRPWM_setMEPEdgeSelect(ePWM[j], HRPWM_CHANNEL_A, HRPWM_MEP_CTRL_RISING_AND_FALLING_EDGE);
    HRPWM_setMEPControlMode(ePWM[j], HRPWM_CHANNEL_A, HRPWM_MEP_DUTY_PERIOD_CTRL);
    HRPWM_setCounterCompareShadowLoadEvent(ePWM[j], HRPWM_CHANNEL_A, HRPWM_LOAD_ON_CNTR_ZERO);
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

  • +1 in reply to Green Deng
    TI__Guru 52010 points

    HRPWM_setCounterCompareShadowLoadEvent(ePWM[j], HRPWM_CHANNEL_A, HRPWM_LOAD_ON_CNTR_ZERO);

    Change this to LOAD on CNTR ZERO AND PRD.

    IT must be CNTR ZERO AND PRD. 

  • 0 in reply to Nima Eskandari
    TI__Expert 4490 points

    Hi Nima:

    In addition, I would like to ask a question.

    Note in the routine: The loading method of CMPA must also be ZERO and PRD.

    In the manual: The loading modes of HRPWM are ZERO and PRD, but actually only the value of the shadow register is loaded at ZERO, and PRD is used for internal logic.

    So will CMPA load the value of the shadow register at ZERO and PRD, or will it follow HRPWM to load only the value of the shadow register at ZERO?

  • +1 in reply to Green Deng
    TI__Guru 52010 points

    So it's a bit tricky. The user must set the load mode to ZERO AND PRD. BUT the user shadow value will only be loaded at ZERO. THE PRD load is used internally to update some internal settings hidden to the customer.