TMS320F28379S: TBCTR is increasing unexpectedly when changing TBPRD during run time.

Pratyush Pandey

Hello,

I have made an algorithm where the frequency of PWM has to be changed while running, I have made the algorithm by changing TBPRD of the EPWM in regular intervals. At lower frequencies, the PWM is working as expected but when trying to switch at high frequencies the TBCTR is increasing unexpectedly (as shown in the figure.)

over 3 years ago

0 Kier over 3 years ago

Mastermind 9850 points

Are you using shadow load mode? If not, then using shadow load mode might prevent this.

0 Pratyush Pandey over 3 years ago in reply to Kier

Prodigy 50 points

Hi Kier,

Thank you for your response. I'm quite new in CCS, so I'll need a bit more help. Can you suggest a literature or source from where i can learn how to implement shadow load mode. Thanks in advance.

+1 Kier over 3 years ago in reply to Pratyush Pandey

Mastermind 9850 points

You're welcome.

If you're already getting a PWM output then you're nearly there. Please refer to chapter 14.4.3.1 Time-Base Period Shadow Register in the TRM: https://www.ti.com/lit/pdf/spruhx5

Having said that I just read that shadow load mode is enabled by default so it's unlikely that you aren't using it and therefore this probably won't solve the issue.

0 Marlyn Rosales Castaneda20 over 3 years ago

TI__Mastermind 27190 points

Hi Pratyush,

Pratyush Pandey said:
when trying to switch at high frequencies the TBCTR is increasing unexpectedly

How are you monitoring the time-base counter?

Would you please provide the value for the TBCTL register as well as the TBCTL2 register?

There is no reason the TBCTR value should be increasing beyond the value defined by TBPRD.

Best Regards,

Marlyn

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TMS320F28379S: TBCTR is increasing unexpectedly when changing TBPRD during run time.