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Original question:

BQ76952: Need your assistance in the schematic and layout

BQ76952: EMI/EMC test issue

Phanidhar M
Prodigy 60 points
Part Number: BQ76952

Tool/software:

Hello team,

We have a designed a BMS and it is detecting all the faults properly. However the issue is that it didn't clear EMI/EMC tests and the IC was going to shut down when the test is being performed. How the BMS IC was going to shutdown is something we failed to understand. What could be the possible causes for this?

Thank you

  • 0
    TI__Expert 8060 points

    Hello Phanidhar,

    Usually, EMI comes from a system level issue that is related to filter designs, PCB layout, components chosen, etc. Do you mind sharing your schematic? Some more filters may need to be added to help.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 60 points

    Hello Alexis_H,

    I have shared the schematic with you in direct message. Please check. And it is a two layer board. 

    Thank you

  • 0 in reply to Phanidhar M
    TI__Expert 8060 points

    Hello Phanidhar,

    Thank you for sharing your schematic. I will review it and get back to you as soon as I can. 

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    TI__Expert 8060 points

    Hello Phanidhar,

    Thank you for your patience. I apologize if I miss some connections, however from what we’ve seen of the schematic, here are our recommendations in general:

    1. D27 and D30 is better not populated
    2. R93 and R96, we recommend 5kOhms instead of 50kOhms
    3. R94 and R95, we recommend 10MOhms instead of 1MOhms
    4. Remove D45 and D44
    5. R82, we recommend 10MOhms instead
    6. Remove D31
    7. Connect D35 to the pin instead potentially
    8. Add more capacitors in parallel at REG18 potentially to help with EMI.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 60 points

    Thanks for your reply Alexis.

    I request you to elaborate point no. 7 and 8 more. What do you mean by connecting D35 potentially? Also, what capacitors do you suggest to connect in parallel? Currently we are using 2.2uF at REG18

  • 0 in reply to Phanidhar M
    TI__Expert 8060 points

    Hello Phanidhar,

    Sorry for the confusion on that point. After re-looking at D35, I realized I mistook where the connection was going. It should be fine as is.

    As for more capacitors in REG18, your 2.2uF is fine, however, because the part is shutting down during EMI/EMC tests, it might be better to add some other capacitors in parallel to help with different frequency ranges. As we don’t know where/why it is exactly failing at, it might be good to experiment with adding other values to see if that helps (.1uF, 1uF, etc.). Unfortunately, I don’t have specific values to provide that would help for sure.

    Best Regards,
    Alexis