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TPA3138D2: Issues getting design through EMC conducted emission test.

hb
Prodigy 20 points
Part Number: TPA3138D2

Tool/software:

Hi,

We have a PoE powered LoudSpeaker using the TDA3138D2 as the audio amplifier into a 4ohm load, in PBTL mode.

The test house has reported -

With the unit not emitting any audio, there is little noise near the limit, however whenever the amplifier is enabled, the noise generated and injected back down the Ethernet cable exceeds the higher Class A (higher) limit 

This is pointing obviously at the Class D amplifier generating noise around 350kHz, which is escaping the unit.

I followed the datasheet with the circuit used, see attached, but i just cant get the design through testing. Any pointers as to what i might have done wrong or need to do? Sorry, having issues understanding how to add the schematic file, if this isn't readable, please provide an email and i'll send it over.

Thanks,

  • 0
    TI__Guru** 108755 points

    Hi,

    I'll review your problem description and get back to you with further comments early next week.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    TI__Guru** 108755 points

    Hi,

    You can try adding an inductor or ferrite at the +12V line, before the decoupling capacitors, to try filtering down the switching noise of the Class-D from the supply.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0 in reply to Ivan Salazar
    Prodigy 20 points

    Hi,

    Are there any app notes that deal with this and the solution. I'm surprised that there is no mention of this issue, which must be present on all designs using this device? 

    I can add a LC filter on the 12V supply but id like to see more detail on this and perhaps approved solutions.
    Thanks.

  • 0 in reply to hb
    TI__Guru** 108755 points

    Hi,

    You may treat the design of a Class-D amplifier similar to that of a buck/boost converter. It follows similar principles of EMI/EMC due to PWM switching.
    I'll double check on previous documentation (although not specific for this amplifier) and share with you soon.

    Best regards,
    -Ivan Salazar
    Applications Engineer