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DP83848J: Risk of damage when RBIAS is 4.87ohm

Shinichi Inoue
Guru 20361 points
Part Number: DP83848J

Dear Specialists,

My customer wrongly connected 4.87ohm resistor to the RBIAS(20pin). It should be 4.87kohm.

In this case, what kind of impact is expected.

We are concerned that the resistance of the RBIAS pin is lower than expected and there is a risk of damage.

I appreciate your great help in advance.

Best regards,

Shinichi

  • +1
    TI__Mastermind 20786 points

    Hi Shinichi, 

    This configuration has not been tested, but there is a possibility it could cause damage. Please switch the resistor back to the 4.87kohm and replace the device if necessary. 

    Thanks,

    David

  • 0 in reply to David Creger
    Guru 20361 points

    Hi David,

    Thank you for your reply.

    I sent your suggestion to the customer and has an additional question.

    Could you please advise.

    ---

    To consider the answer and other threads about RBIAS,

    RBIAS speculated that it was determining the reference voltage for sending and receiving data.

    In our board, although DP83848 is mounted on the board, the Ethernet circuit is not used (because it is an option), and the cable is not connected.

    Therefore, there is no change in input / output, and we consider that there is no effect on the device.

    We think that the worst case you mentioned is for all cases when a resistance value other than the specified one is connected.

    Our conclusions are as follows, are these correct?

    1) Since the reference voltage is abnormal, the transmission / reception judgment criteria will change, and normal judgment cannot be made.

    2) Since the operation cannot be guaranteed, if it is operated, it may lead to the failure of the device in the worst case.

    3) At our company, DP83848 is mounted but not used, and the cable is not connected. There is no risk of damage in this state.

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Mastermind 20786 points

    Hi Shinichi, 

    I agree with your conclusions. There is no way for us to know whether the device is damaged, so you can replace the devices proactively or continue using it to see if operation is still normal, but we cannot guarantee normal operation. 

    Thanks,

    David

  • 0 in reply to David Creger
    Guru 20361 points

    Hi David,

    Thank you for your reply.

    I'll share your answer with the customer.

    It's strange to me the device is  mounted on a board and doesn't use any circuits, but the customer will be relieved that there is no risk of damage.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to David Creger
    Guru 20361 points

    Hi David,

    The customer satisfied with your suggestion.

    Let's close this thread.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 20786 points

    Good to hear. Closing this thread. 

    Thanks,

    David