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LM5000: EMC test fail

Tommy Tzeng
Genius 5400 points
Part Number: LM5000

Hi Sir,

when testing EMC, there will be fail when testing the cinduction test(ISN 100M), where in the schematic can the situation be improvde?

may we learn from you, thanks.

  • 0
    TI__Mastermind 18655 points

    Hello Tommy,
    Thanks for reaching out to us via e2e.

    I assume that the 798 kHz is the switching frequency.
    Can the 334 kHz be caused by the motor / motor driver?
    Would selecting the 300 kHz mode (connecting the FS pin to GND) be a possible option?

    The layout plays an important role to avoid radiation of the switching frequency.
    All power loops (on the input side and also on the output side) have to kept as small as possible.

    Things to try to reduce the radiation of the switching frequiency:
    - Select a different diode which is slower than the diode you are currently using (You can also try a faster one, but I am not sure about that)
    - Add a smaller (maybe 100 nF) ceramic output capacitor (Low ESR, Low ESL and RF capable) as close to the diode as possible
    As a first step, maybe replace C60 or C61 (whichever is closer to the diode) with this capacitor mentioned above.
    - Also add a Low ESR Low ESL ceramic capacitor on the input side (as close to the inductor as possible)
    - Try adding a snubber (RC filter) from SW to GND.

    Please let me know your results.

    Best regards,
    Harry

  • 0 in reply to Harry Hofner
    TI__Mastermind 18655 points

    Hello Tommy,

    As this is a conduction test, which is failing at the switching frequency (798 kHz), you can tell that the signal is going back through the cable to the source. If the measures mentioned above do not help to improve the situation you may need to add an input filter.

    Best regards,

    Harry  

  • 0 in reply to Harry Hofner
    TI__Mastermind 18655 points

    Hello Tommy,

    I have not seen an update from you for nearly two weeks,

    Did you manage to pass the test?

    Was it enough to change some components or will you need to add a filter?

    Thanks and regards,
    Harry