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DP83848K: design

Ahmed Tuna
Prodigy 115 points
Part Number: DP83848K


Hello TI Engineers,

I have a service request which the customer asks the questions below. Can you please provide some answer for the customer?

Customer’s request;

“ I am using DP83848K Ethernet transceiver interface with the MCIMX6U6AVM08AB Processor.

1.Mode selected for my application is MII . The clock for Ethernet transceiver is 25Mhz which can be sourced from Clock or oscillator.

My question is  Can this 25MHz to the Ethernet transceiver be sourced from the clock generated in the Processor? Will it work?

2. I hope the Rbias resistor is used to set-up critical bias currents. In my design , I have used an RJ45 connector(J0011D21BNL) with integrated transformer. The recommended resistor and capacitor are used for TPI network

Please clarify how should I calculate power consumption ? How to calculate ICT

3.My design uses external PI and RC filters between the PHY and RJ45 . Is it recommended  to have it for filtering ?

Additional question;

In Datasheet the maximum power dissipation is 264mW. The Idd10 current is 92 mA(typical). VDD is 3.3V. The calculated power is 303.6 mW which is exceeding the datasheet limits . How is the maximum power calculated? "

Thank you.

Best regards,

  • 0
    TI__Mastermind 23675 points

    Hi Ahmed,

    A1) You can source the clock from a processor so long it does not have excessive jitter. Check with the processor team to see if they have successfully used their output clock with PHYs before. The DP83848 clock requirements are in the DS.

    A2) Consumption is both in the PHY and on the CT. Please review this app note: 

    A3) Please send a schematic and we can have a look. 

  • 0 in reply to Ross Pimentel
    Prodigy 100 points

    HI ,

    Please find the screenshot of the schematics below.

    Some RC combinations and Pi LC filter is used

  • 0 in reply to Ross Pimentel
    Prodigy 100 points
    Hi,

    Considering the worst case from App note, the maximum power dissipation at 100base- T mode is 337.8mW. The datasheet shows the maximum dissipation as only 264 mW. Please clarify if the Power dissipation in datasheet is rated for worst case or base line.
  • 0 in reply to Gkarthik
    TI__Mastermind 23675 points
    Hi Gayathri,

    The application note is correct. There should not be a max power rating in the ROC portion of the DS.
    Sorry for the confusion.

    As for the PI filter, please ensure it is a low pass with the knee around 10MHz.
    When in 10Mbps operation, the signaling is Manchester and the frequency is 10MHz.
    When in 100Mbps operation, the signaling is MLT3 and the frequency is 125MHz.