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TMS320F28379D: Jitter on HRPWM output

Marton Kovacs
Prodigy 50 points
Part Number: TMS320F28379D

Hi everybody,

I have a problem with HRPWM on TMS320F28379D if the phase shift is enabled.

If the HRPWM feature is enabled only for one channel without the syncronisation between the modules it is working properly, but if the PWM modules are working in phase sift mode (PHSEN = 1) and the HRPWM feature is enabled in parallel the following jitter can be observed on the output:

  • PWM module: PWM2
  • duty cycle: 3%
  • pulse width: 0,03 * 10417 ns = 312,5 ns
  • target compare value: 15,625
  • target CMPA: 15
  • target CMPAHR: 0,625 * 216 = 40960
  • EPWM2SYNCI = EPWM1SYNCO: CTR=ZERO (SYNCOSEL = 01)

I tried a lot of settings regarding to the load configuration, shadow registers and phase shifting but only the location of the jitter moved the jitter was not eliminated just if I set back PHSEN = 0.

Could you please help me which setup is required for the HRPWM and Phase Shift to remove the jitter on the output?

Thanks you in advance!

Regards,

Marton

  • 0 in reply to Marton Kovacs
    Prodigy 50 points

    And the jitter if the phase shift is also enabled:

  • 0 in reply to Marton Kovacs
    TI__Intellectual 1360 points

    Hi Marton,

    Could you provide the following information:

    1. The phase value setting.

    2. Source of PWMSYNC, and the period of PWMSYNC.

    Regards,

    Srinivasa

  • 0 in reply to Srinivasa Chakravarthy
    Prodigy 50 points

    Hi Srinivasa,

    thank you for your reply!

    1. on PWM2:

    TBPHS = 260
    TBPHSHR = 0 -> for the test the fractional part of the phase shift register was not changed

    2. PWMSYNC is generated by PWM1 for the PWM2. PWM1 triggers sync signal if the CNT=ZERO, and PWM2 uses this sync signal for counter register loading and pass on to the SYNCO.

    Detailed settings

    PWM1 and PWM2 common settings
    EPWMCLK: 100 MHz
    CTRMODE = 0b10 -> up-down counting mode

    target frequency: 96 kHz
    target period: 100000/96/2 = 520,8333
    TBPRD (integer part) = 520
    TBPRSHR (fractional part in Q15 format): 0,8333 * 2^16 = 54613

    HRMSTEP = 66 -> 10ns / 150ps = 66
    HRLOAD = 0b10 -> Load on either CTR = Zero or CTR = PRD
    AUTOCONV = 0b1 -> Automatic HRMSTEP scaling is enabled.
    EDGMODE = 0b11 -> MEP control of both edges
    TBPHSHRLOADE = 0b1 -> Synchronize the high-resolution phase on a SYNCIN
    HRPE = 0b1 -> High resolution period enabled


    PWM1 settings

    PHSEN = 0b0 -> phase shift is disabled
    SYNCOSEL = 0b01 -> SYNCO = if(CTR=ZERO)


    PWM2 settings

    SYNCOSEL = 0b00 -> SYNCO = SYNCI
    PHSDIR = 0b0
    PHSEN = 0b1 -> phase shift is enabled
    TBPHS = 260
    TBPHSHR = 0 -> for the test the fractional part of the phase shift register was not changed

    Regards,

    Marton

  • 0 in reply to Marton Kovacs
    TI__Intellectual 1360 points

    Hi Marton,

    I suspect the following:

    * You are using hires period.

    * PWMSYNCOUT generation is based only on the integer value of period.

    which is probably why you see a jitter on PWM. Can you experiment, by not using hires period, to confirm  ?

    Regards,

    Srinivasa 

  • 0 in reply to Srinivasa Chakravarthy
    Prodigy 50 points

    Hi Srinivasa,

    thank you for your help! I disabled the continguous Phase shift loading on sync event, because it seems that was the reason of the jitter in HRPWM mode.

    Best regards,

    Marton