TMS320F280039C: Generic question about EPWM count mode selection

Johnny Chen

Part Number: TMS320F280039C

Tool/software:

Hi Champ,

I am asking for my customer for digital power doing server PSU.

It is a generic question about is there a rule of thumb to determine EPWM clock mode with up count mode or up-down count mode ?

In general, up-down count mode is mostly selected as TB clock counting.

There must be some reasons and pros. for selecting the up-down mode, is it because of TB resolution or depending on topologies to ease to configure the EPWM ?

Thanks for the comment.

Regards,

Johnny

over 1 year ago

0 Srikanth Yerra over 1 year ago

TI__Intellectual 1890 points

Hi Johnny,

With up-down count mode you can generate symmetric PWM centered around period, where as up-count mode gives asymmetric PWM. Symmetric PWM has advantages in specific applications like AC/DC converters and motor drives to reduce the harmonic content. In contrast some of the DC-DC converters may use asymmetric PWM. Overall it depends on the application needs.

In addition with up down count mode High Resolution PWM can be configured for both rising and falling edges, but up count mode allows HRPWM for rising edge only.

Thanks

Srikanth

0 Johnny Chen over 1 year ago in reply to Srikanth Yerra

TI__Expert 5090 points

Hi Srikanth,

Thanks for the input.

I also learned from this post which explained the harmonic reduction with symmetric PWM configuration.

https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/706160/tms320f28035-symmetric-vs-asymmetric-pwm

It is said that "Asymmetric mode is often used in things like DC-DC converters - using this you are able to get an extra bit of resolution in your ability to control the duty cycle (vs Symmetric). " from the post.

Is it true that the Asymmetric mode could get an extra bit of resolution (vs Symmetric) ? What's conceptual reason of this statement ?

Thanks and regards,

Johnny

0 Srikanth Yerra over 1 year ago in reply to Johnny Chen

TI__Intellectual 1890 points

Hi Johnny,

That statement maybe made in particular to the device mentioned.

But with F280039x, you can have high resolution of both rising and falling edges in Symmetric mode.

Thanks

Srikanth

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TMS320F280039C: Generic question about EPWM count mode selection