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DP83848I: about DP83848 input oscillation issue

Vera Mao
Expert 5065 points
Part Number: DP83848I

hi dear supporting team,

My customer is using DP83848IVV， and found there is oscillation happens  at the input, frequency measured as 2.5GHz.  detail as below, pls help suggest whether it is due to layout or other possible cause. . And customer hope TI could help reproduce the issue on our EVM by loopback TX to RX  and replace the transformer with a cap. Tks a lot!

  1. BCM5482 (PHY) connect to DP83848,  this is old brd, and in field they always found BER,  after trouble shooting, they found there is high frequency at Vih

    signal.  Topology as below:

  2. If test at BCM side, there is no such oscillation.

  3. Remove 3.3V bias, there will be no oscillation as well.

  4. If replace the 0.01u cap with a balun, the oscillation will also disappear.

  5. Disconnect BCM5482 by removing the 0.01u cap, there will be no oscillation as well.   (there is only DC voltage at 83848 SIDE)

  6. The layout of DP83848 is as below:  both DP83848 has the issue, the yellow portion is the DIFF  trace,  read is top layer, blue is bottom, the DIFF  trace is route through top, bottom and 10th layer.  

    attached is the sch they are using. dp83848-xxxx.pdf

 BTW, do you have the model of DP83848 that could be used to simulate the ethernet  electrical port?