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DP83848C - I'm loosing lots of devices...

Andrew Frazer
Expert 2305 points
Other Parts Discussed in Thread: DP83848J

I'm using a DP83848CVV, with a POE circuit, and a    When it works it works very well, and i have no problems.   However from time to time the PHY dies..  Replacing it fixes the problem...     With non POE stuff they are rock soild.   I've put TVS diodes across the Line side of the transformer and that helped. 

I'm now thinking i shoudl put TVS didodes on both sides of the Transformer, so i can protect against both differential and common mode issues.

What else can i do to make things more reliable.

Is there a more roubust PHy?

  • 0
    TI__Mastermind 23675 points
    Hi Andrew,

    Could you provide more detail as to how the device is behaving when it "dies"? Any screen shots of the waveforms would help.

    What does RBIAS read before and after?
    Does the SMI work after?
    Do you see TX_CLK and RX_CLK after the event?
    What is the current consumption like before and after?

    Does a power cycle not work?

    Kind regards,
    Ross
  • 0 in reply to Ross Pimentel
    Expert 2305 points

    The faults generally occcur when the device is *unplugged* from a live Port.  I'm suspecting that whats happening is that when the connection is broken, one side of the transformer is disconnected before the other..   The result is that momentarily theres ~50V difference which makes its way across the transformer, hits the phy and kills it.     

    I get a variety of different outcomes;

    (1) High Current, is quite common, ( and it gets hot! )

    (2) Completely unresponsive.. nothing on teh CLKREF pin.. nothing on TX_CLK, RX_CLK

    Repowering does'n fix it. Replacing the PHY does.

    Do you happen to have a reference design for using the PHY with a POE? 

  • 0 in reply to Andrew Frazer
    TI__Mastermind 31600 points
    Andrew,

    We do have some reference designs for PoE. You can find them on our Ethernet reference designs page:
    www.ti.com/.../ethernet-reference-designs.page

    On that page, please see the information for the "DP83848J/K POE Board" and the "DP83848 Rock Hopper Demo II Board".

    Patrick
  • 0 in reply to Patrick OFarrell
    Expert 2305 points
    Hi Patrick

    I had a look at that reference design. What i did'nt see was any TVS diodes etc on the PHY or cable side of the transformer.. That did suprise me a little. How does this PHY protect itself against thigns like Cabl discharge, or hot disconnects? Is it somehow built into the phy itself?