• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 81 subscribers
  • Views 503 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F28035: Analog Comparator giving False Trigger to EPWM module

Siddharth Sharma1
Intellectual 445 points
Part Number: TMS320F28035

Hi all,

I am are using Analog Comparator for detecting Short Circuit fault (OSC) in my application. My application is to make PSFB controller and switch off EPWM(which drives mosfets) whenever current rises more than threshold range(60 Amps in my application). PWM will be switched-off by generation of Trip Zone signal (OST action) by the Comparator. The reference value for the Comparator is given by DAC. 

The problem I am facing is that many times OSC is getting falsely triggered. Even though current has not reached to 60 Amps(By probing verified it), still OSC is getting detected. On debugging the problem, we also saw that this problem is more frequent when we switch off the PWM. We normally do hard switching off of the PWM.

For example, Current getting pumped around 10 Amps and in some event we switch off PWM. In that case, we find OSC getting falsely triggered.Although current is well below the threshold.

We have tried following solutions to make this work :- 

  1) Make Current Zero and then after 20 ms switch off the PWM.

  2) Make Comparator Logic Disable before switching off the PWM. 

Both the solutions didn't worked. For getting OSC status , i am using TZFLG[OST] bit status.

I am not able to understand why it is getting falsely triggered. Anyone please suggest me possible solution for that. 

Is there any Chip Level problem in Analog Comparator?    Sir can you please guide me regarding it.?

Thanks

Regards

Siddharth 

  • 0
    TI__Guru 62975 points
    Siddharth,

    Are you seeing this behavior with just one device or multiple?

    I recommend that you set aside the full PSFB application for a moment and focus only on a small debug program to observe the comparator output when you drive arbitrary voltages onto the comparator input. This should allow you to verify that the comparator is behaving as you expect on your device/board before continuing with more complex debug.

    -Tommy
  • 0 in reply to tlee
    TI__Guru 62975 points
    Siddharth,

    It has been over a week since your last update. I assume that you were able to resolve your issue. If this isn’t the case, please reject this resolution and reply to this thread. If this thread is locked, please make a new thread describing the current status of your issue.

    -Tommy
  • 0 in reply to tlee
    Intellectual 445 points
    Tommy,

    Sorry for late reply. I tried above solution by giving arbitrary voltages, but comparative behaves correctly.

    Currently, i am out of any options.
    One thing i am pretty sure whenever we are switching PWM off then only comparator is getting false triggered.

    Let me know if you need some code snippet for the easy identification of the problem.

    Thanks
    Regards
    Siddharth
  • 0 in reply to Siddharth Sharma1
    TI__Guru 62975 points
    Siddharth,

    Are you able to put a scope probe on the comparator input and output pins when the OSC trips? It would be worth checking to see if there might be noise coupling onto the comparator input that causes the trip.

    -Tommy
  • 0 in reply to tlee
    TI__Guru 62975 points
    Siddharth,

    Did you find anything?

    -Tommy
  • 0 in reply to Siddharth Sharma1
    TI__Guru 62975 points
    Siddharth,

    It has been over a week since your last update. I assume that you were able to resolve your issue. If this isn’t the case, please reject this resolution and reply to this thread. If this thread is locked, please make a new thread describing the current status of your issue.

    -Tommy