TMS320F280049: PCMC for PSFB topology: Abnormal CTRIPOUTH signal

Sheldon He

Hi expert,

Happy holiday. My customer have issue doing peak current mode control in PSFB. We narrow down the issue and find CTRIPOUTH gives out strange pulse occasionly which is not expcted.

As shown above:

Yellow：outputXbar to indicate CTRIPOUTH

Blue：EPWM5A

Pink：Primary side Current

Typically CTRIPOUTH will have a length of 200ns in high level, while sometimes it gives a very small signal. We are using event T1 to trigger two EPWM modules (4 and 5) action qualificaiton submodule while only one of these two get triggered (It could be primary side current was shut down so the other is not triggering).

Key point: We only meet this when we are using ASYNCH mode, if we are using digital filter of CMPSS, everything will be fine, as shown below:

What are the differences here for ASYNCH and signal after digital filter?

Why we get this stange pulse?

Thanks

Sheldon

over 5 years ago

0 Himanshu Chaudhary60 over 5 years ago

TI__Expert 3720 points

Hi,

The subject matter expert assigned to this thread is out of office this week due to the end-year holidays so you may not get a qualified answer until Jan first week. I apologize for the delay.

Regards,

Himanshu

0 Frank Ankapong over 5 years ago

TI__Mastermind 28275 points

Hi Sheldon,

Asynch is the raw un-synchronized output from the comparator. Unless you need the fastest trip possible and have a relatively noise free system, it's better not to use the Asynch output. The filter as the name says synchronizes the asynch signal and also filters it to remove noise. This is documented in the TRM.

0 Sheldon He over 5 years ago in reply to Frank Ankapong

TI__Expert 8585 points

Hi Frank,

Thanks for your response.

But we still like to know in what conditions could we see output like this? (Very narrow output pulse) Does that mean the signal we compare to reference is not monotonic? Or does that mean comparator reference has some fluctuation?

My customer need to explain this to their manager and make some record on our devices.

Thanks

Sheldon

0 Frank Ankapong over 5 years ago in reply to Sheldon He

TI__Mastermind 28275 points

Sheldon,

Yes, the compdac reference can have fluctuations if it is connected to VDDA as any noise on VDDA will directly couple to it. Can you confirm that the compdac reference is set to VDDA?

0 Sheldon He over 5 years ago in reply to Frank Ankapong

TI__Expert 8585 points

Hi Frank,

Yes, they are using VDDA which is by default.

Thanks

Sheldon

C2000™︎ microcontrollers

C2000 microcontrollers forum

TMS320F280049: PCMC for PSFB topology: Abnormal CTRIPOUTH signal