TMS320F280039C: Using Enhanced Pulse Width Modulator (ePWM) Module for 0-100% Duty Cycle Control Application Report

Hi Wayne,

I am looking into your query, will respond before thursday.

Best,

Uttam

Dear Uttam,

Is there any update?

The user has seen unexpected waveforms when setting CMPA=0 (supposed to be 0% duty but 100% intermittently for a PWM cycle), so they are analyzing this and want us to clarify conditions and symptoms of this boundary issue.

Wayne

Hello Wayne,

Sorry for the delay, this thread has been re-assigned to Luke. He will get back to you as early as possible.

Best,

Uttam 

Hey Wayne, apologies for the delayed response on this thread, I am looking into this now.

Hey Wayne,

Is this the issue from the thread you are referring to?

"On type 0 EPWM, like device F2808, it seems CMPA will be loaded as 0 once TBCTR=0, and then the comparison action will be ignored thus CAU event will NOT occur so output high will not work"

If this is correct:

"ONLY when CMPA/CMPB is from 0 to a non-zero value"

Do you actually mean from non-zero value to 0, or was this intentional?

"ONLY for up-down count (that is, excluding up-count and down-count)."

I believe this condition is independent of the count-mode but rather whether the counter is incrementing or decrementing. So for example a load of CMPA = 0 in up-count mode could result in the same ignored event.

Thank you,

Luke

Dear Luke,

We are still confused.

In fact, the user just wants us to clarify all the conditions and considerations when using CMPA/CMPB=0 in up-count and up-down count and what are the symptoms and their occurrence freq. (always or intermittent) because TRM 20.6.5 Waveforms for Common Configurations and the post in the original post confuse us.

For example, TRM 20.6.5 Waveforms for Common Configurations says:

"To achieve 0-100% asymmetric PWM use the following configuration: Load CMPA/CMPB on TBPRD. Use the Zero action to set the PWM and a compare-up action to clear the PWM. Modulate the compare value from 0 to TBPRD+1 to achieve 0-100% PWM duty."

Why it asks to Load CMPA/CMPB on TBPRD rather than on ZRO? Isn't ZRO and PRD at the same cycle on TBCTR=0 for up-count mode? Is load on TBPRD a must when using CMPA/CMPB=0?

For example, the referred post says, it is only for up-down count which implies up-count does not have this concern. But does F28003x type-4 PWM still the same as that on the post?

For example, the app note "spraai1" says, this would happen from CMPA/CMPB = 0 to non-zero as well as from non-zero to CMPA/CMPB = 0, and in TRM 20.6.5 Waveforms for Common Configurations, it includes this app note. Why?

All these confuse the users, who just wants to confirm how to use CMPA/CMPB=0 in a right way.

Would you please help clarify?