Problems when enable option IMMEDIATE of CMP Reg Load On ePWM block

Altair Forum User

Submitted by marcelmsl on Fri, 12/28/2012 - 18:26 

 

Hi,

I'm having problems when I enable the option IMMEDIATE CMP Reg Load On ePWM block. Attached are figures with example of where I'm doing and the block configuration ePWM.

In PWM output pin put an RC filter to reproduce the sinusoid. However, there pulses do not know where that's going, like failures when comparing sine and triangular waves, for example. The attached figure show the result of the sinusoidal and triangular waves PWM and reproduced.

I would appreciate your help to fix this. Urgent need of results, because I have to finish the project report.

Thank you.

Unable to find an attachment - read this blog

Altair Forum User

Submitted by Anders89 on Sun, 12/30/2012 - 00:04.

The problem appears to be your use of 'Immediate Update' to the PWM compare registers. Because the PWM waveform logic uses an exact match between the compare register and the count as a waveform switch event, and because you have chosen to update the compare register immediately, it is possible that you can update the compare register in such a way as to skip over the match event and lose a PWM switch, which can cause the PWM level to stay high or low for an entire cycle.