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UC2843: EMI issue

Kiyong SON
Intellectual 545 points
Part Number: UC2843

Dear TI-er

My customer have EMI issue.

UC2843 is occured to EMI issue in the board.

Normal case is from 95kHz to 96kHz frequency.

Worst case is from 100kHz to 105kHz frequency.

How I correct it ?

plz help me.

  • 0
    TI__Genius 13660 points

    Hi Kiyong,

    I need more details about the specific of iuuse:

    1, is a conduct or radiated EMI iuuse?

    2. is adc-dc or ac-dc application?

    3. what does worst case mean? Fsw variation?

    4. is the issue local noise issue?

    Besides, the free oscillator is 95~96 kHz in the schematic, and the sync pulse signal should has a larger frequency than free oscillator. 

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Intellectual 545 points

    It is correct the word.

    Good sample - EMI pass case is from 95kHz to 96kHz frequency.

    Bad sample - EMI fail case is from 100kHz to 105kHz frequency.

    He is try to A-B-A swap test.

    Bad sample is occured the issue at Good board.

    Is it the frequency in the deviation ?

    I will check your question to my customer.

  • 0 in reply to Kiyong SON
    Intellectual 545 points

    Hi TI-er

    1, is a conduct or radiated EMI issue?  It is not EMI issue.

    2. is dc-dc or ac-dc application? AC-DC SMPS.

    3. Fsw variation? N/A

    Good sample - Good pass case is from 95kHz to 96kHz frequency.

    Bad sample - Noise issue case is from 100kHz to 105kHz frequency.

    4. is the issue local noise issue? It is noise issue on the screen and the UC2843 gives direct impact to the noise.

    Besides, the free oscillator is 95~96 kHz in the schematic, and the sync pulse signal should has a larger frequency than free oscillator. Yes, of course.

  • 0 in reply to Kiyong SON
    TI__Genius 13660 points

    Hi Kiyong,

    Do you solve this issue?

    May I know what is the frequency of sync signal? Typically it should be 20% higher than the free frequency.

    Because according the datasheet, there maybe be 15% maximum error of  free oscillator, 10% at 25C, and 5% over temperature. You can check the free frequency of good and bad device.

    Regards,

    Teng