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TUSB211: EMI problem with TUSB211

Peter te Vaarwerk97
Prodigy 50 points
Part Number: TUSB211

Hello.

In our application (a camera with USB2.0 interface) we have serious problems with emissions on 480MHz and 960MHz.

The camera has a 3 meter cable connection to the USB interface.

The USB connector is mounted on a PCB where we added a current protection circuit and a TUSB211 signal conditioner.

The signal conditioner is required to have a good eye pattern, especially at the moment we will be using an extension cable (1 or 2 meter).

The emission levels are approximately 10 dB above the limits. The equalisation factor is set to level 1.

The PCB layout is according the datasheet proposal.

The signal conditioner is mounted very closely to the USB connector. We believe that the emission is coming from injecting current into the datapair.

We tried several PCB layout concepts, shielding concepts but nothing seems to work properly.

We tried to add common mode coil, this improves about 10dB (we need to have some more).

Any suggestions would be highly appreciated .... 

  • 0
    TI__Mastermind 36085 points
    Hello Peter,

    I am reviewing the issue and I will try to provide a suggestion soon, I just need to know whether the EMI issues are during HS transactions, or while the TUSB211 is trying to detect a HS signal (no connection or FS/LS connection). Also please share the eye diagram, it will be useful to plan a next step.

    Regards,
    Diego.
  • 0 in reply to Diego Cortes
    Prodigy 50 points

    Hello Diego,

    Answer to your questions:

    Below is also the eye diagram. In this diagram you can see some jitter (we think it is caused by the cable).

    Some more info during evaluation we did yesterday. Common mode coil between the TUSB211 and USB connector seems to help.

    We think the problem is caused by the current injections towards the laptop. There is also differences if different laptop usb ports are used.

    We made a perfectly shielded EMC-HUB, and if we connect this EMC-HUB between laptop and camera then the emissions are within the limits.

    Thanks

    Best regards

    Peter

  • 0 in reply to Peter te Vaarwerk97
    TI__Mastermind 36085 points

    Thanks for the feedback,

       I would try two things:

    1. change the EQ level to 3.
    2. Try to decrease the drive strength on the USB port.

    Show me your findings using both options.

    Regards,

    Diego.