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TSB81BA3D IEEE1394 Firewire cable connection questions

Bryan Busacco
Expert 1215 points
Other Parts Discussed in Thread: TSB81BA3E

In looking at the TSB81BA3D datasheet ( SLLS559E ) page 22, we have questions regarding cable/connector connections.

Is chassis GND on this diagram connected to the frame of the connector ( thereby connecting it to the outer cable shield )?

On the diagram, are all GND symbols ( pictured the same on the diagram ) really chassis GND? We ask because only one instance is actually labeled chassis GND.

We are trying to understand the grounding scheme for the cable, connector, signal GND and Chassis GND. Any input would be appreciated.

 

Thanks, Bryan.

  • 0
    TI__Guru* 76130 points

    Hello Bryan,

    Please see the attached picture. The symbols in the red circle are signal grounds, and the symbols in the green square are chasis grounds.

    By the way, the TSB81BA3D is not recommended for new designs, we recommend the TSB81BA3E.

    Regards.

  • 0 in reply to Elias Villegas M.
    Expert 1215 points

     

    Is it proper to assume that "CHASSIS" GND is the frame of the connector?  This would make the shield of the cable a CHASSIS GND connection, in addition to the shield of CABLE PAIR A and CABLE PAIR B.

    Thanks, Bryan.

  • 0 in reply to Bryan Busacco
    TI__Guru* 76130 points

    Hello Bryan,

    I apologize if the above figure is a little confusing, here is the propper connection:

    1) The shield of the signal twisted pairs should be connected to the VG pin of the connector.

    2) The shield of the 1394 cable should be connected to the plug shield shell.

    Regards.

  • 0 in reply to Elias Villegas M.
    Expert 1215 points

     

     

    Three more questions, then I think we'll have it.

    1) How do you recommend we deal with the traces passing between the TSB81BA3D and connector? Should we have traces on the top layer with a GND plane on the layer directly beneath it? Or should we have a void in the layers of the PCB?

    2) In this dsign we have 3 seperate Firewire links with 3 connectors on the board edge very close to each other. Should each connector have it's own "CHASSIS" GND, or should we connect all 3 shells together ( for example with 1 solid  CHASSIS GND plane under all 3 connectors ).

    3) I just had a thought. Is there a TSB81BA3D eval board? If so we could probably learn all we want by looking at it's board layout.

     

    Thank you,

     

    Bryan.

  • 0 in reply to Bryan Busacco
    TI__Guru* 76130 points

    Hello Bryan,

    1) You can find a design guide in the following link: http://www.ti.com/lit/an/slla117/slla117.pdf

    2) It is OK to connect all the shell's shields together.

    3) The TSB81BA3D is NRND (not recommended for new designs),  I recommend you to use the TSB81BA3E which is active and evaluation boards are available to order.

     

    Regards.