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TAS5630 and EMC problems

trond inge wang
Intellectual 385 points
Other Parts Discussed in Thread: TAS5630

 

Hi TI,

we have EMC problems which we think origin from the TAS5630. We have copied the evaluation kit and the frequency is now set by a resistor. We see that the part has an external clock input. Could this input be used for a spread spectrum clock oscillator? Oscillators like this are in sale to help solve EMC problems.

Trond Inge Wang

 

 

 

  • 0
    TI__Guru**** 189399 points

    Hi, Trond,

    I'm thinking our chip will not like having the clock being jerked around, and you might end up with audio artifacts from that.

    We usually just fix EMC problems with PCB layout and filtering techniques.

    I have asked one of my colleagues to work further with you. You can either post your schematics and layout here, or we can go offline if you prefer.

    -d2

  • 0
    TI__Mastermind 37045 points

    Hi Trond,

    I sent you a "add a friend" request. After you accept it, you can share your schematic and layout with me privately.

    reg,

    Paul.

     

  • 0 in reply to Don Dapkus
    Intellectual 385 points

    Hi Ti,
    wanted to have our equipment with the TAS5630 EMC certified, but ran into a problem with the frequency component at 400kHz. The component was picked up by a magnetic loop antenna. We use PBTL mode and BD mode. On our board the 4 toroids in the LC filter are in parallell mechanically. Back to the lab I discovered that if the winding direction was reversed for 2 of the coils, the 400kHz component was drastically reduced due to cancellation. I also tested with coils that looks like the 7G17-100M from Sagami in the same way and they are even better.


    Do you have any experience in reducing the emitted magnetic field at 400kHz from the filter coils?
    On the TI evaluation board it is not possible to make a cancellation since the coils are mounted 90 degr. to each other.


    best regards
    Trond Inge Wang

  • 0 in reply to trond inge wang
    TI__Mastermind 37045 points

    Hi Trond,

    Did it pass the EMC test with the new inductor placement to cancel the field? Did you use toroid inductor similar to the EVM?

    Increase the output LC filter order or double the inductance  (with the same current rating) can also help 

    reg,

    Paul.

     

  • 0 in reply to user5276421
    Intellectual 385 points

     

     

    Hi Paul,

    we did not pass the test (14dbuV/m above limit) , but will try again next week to see if the cancellation trick  works out. We are using toroid inductors similar to EVM.

    In the testhouse, I noticed that the emission was not influenced by a resistive load (loudspeaker connected). I think this is because the cap (680nF) in the filter is nearly a short for 400kHz and that the toroid works as a "magnetic" antenna for the current that runs through it. That makes me also think that an additional filter section will not help (I have not tried this).  Your comments are appreciated.

    They tested with methods specified in CISPR 16-1 with a magnetic loop antenna at a distance of 3 meter.

     best regards

    Trond