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UCC28070A: UCC28070A

Abhiman Hande47
Prodigy 60 points
Part Number: UCC28070A

We are noticing an abnormal current spike on input current waveform at higher loads. Here is a picture of the waveform (Ch8=IinAC). We can see some distortion towards the top of current waveform.

This issue only occurs at higher input currents. Here is another picture with current sense signal (pin 9 of UCC28070A). Ch5=CS pin 9 of UCC28070A, Ch8=IinAC. The current sense signal seems to be lower than peak current limit.

Things tried so far. Increased peak current limit. Added more filtering on CS signal. Modified current loop to reduce cross over frequency. Issue still persists. Please advise on possible causes of this distortion and things to check/modify to eliminate this.

Thanks

Abhiman

  • 0
    TI__Mastermind 26225 points
    Hi Abhiman,

    I suggest checking IMO and VINAC pins. Check to see if you see the same distortion. VINAC is the sampled rectified AC voltage and IMO is the output of the current multiplier. Distortion in these signals could distort the reference used by the CA1/CA2 amplifiers.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    TI__Mastermind 26225 points
    Hi Abhiman,

    Just wanted to check if you were able to make any progress in your debug efforts. Please let me know if this issue needs further attention.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 60 points

    Hi Ben,

    Thanks for your suggestions. We tried checking VinAC and IMO. But adding probes there distorted the reference signal and current waveform.

    We decreased the sense resistor value on our current sense transformer to increase the peak current limit. This solved the issue.

    But the current sense waveform didn't appear to be hitting the peak current limit (3.6V) before the fix. Also, the peak power limit (RIMO) is set for much higher power. So, I am not sure why increasing the peak current limit fixed the issue. If you have any insight on this, please let us know.

    Thanks for your help.

    - Abhiman

  • 0 in reply to Abhiman Hande47
    TI__Mastermind 26225 points
    Hi Abhiman,

    Based on your description, I think perhaps the larger sense resistance was allowing for more noise to couple into the CS signal. I don't think the issue was caused by the peak current limit setting.

    Best Regards,
    Ben Lough