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TLK105 / Bob Smith Termination

Ryuji
Guru 20090 points
Hello,
 
I would like to know about Bob Smith termination.
Please see the attached file as  bob smith termination schematics.
 
Page 1 is our schematics and Page 2~4 is Bob Smith termination from some application note or user's Guide.
I could found some pattern of Bob smith termination.
Could you please let me know whether our bob smith termination is correct or not ?
 
Best Regards,
Ryuji Asaka
 
 
  • 0
    TI__Mastermind 31600 points

    Asaka-san,

    There are two topologies that I commonly see for Bob Smith terminations. For standard Ethernet applications, 75 Ohm resistors connect to a common point that is coupled to ground via a capacitor.  For Power over Ethernet (PoE) applications, the 75 Ohm resistors are individually capacitively coupled to prevent DC current flow. 

    Your termination appears to be a blend of these two approaches.  The 75 Ohm resistors to the RJ-45 connector include the additional coupling capacitors, but the 75 Ohm resistors to the transformer do not. 

    Are you designing for PoE?  If so, I would recommend adding coupling capacitors for the 75 Ohm resistors to the transformer.

    Patrick

  • 0 in reply to Patrick OFarrell
    Guru 20090 points
    Hello Patrick san,
     
    Thank you for your prompt reply.
     
    RJ45 is used for PoE alternative A
    And transformer  is used for data only.
    Thus, the schematics is blend of two approaches.
     
    Best Regards,
    Ryuji Asaka