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AM3352: AM335x with DP83822

paddu2017
Expert 2885 points
Part Number: AM3352
Other Parts Discussed in Thread: AMIC110, DP83822I

Hi,

Our AM3352 based application will be using DP83822 as Ethernet PHY(CPSW).
And there is a little confusion about Ethernet Resistor Strapping.

We couldn't find EVMs other than ICE board to refer AM335x + DP83822 schematics.
In case of AMIC110 ICE, the user guide mentions that Software should turn off internal pull resistors
of these pins to prevent AMIC110 internal pull resistors from interfering with the bootstrapping of Ethernet PHY.

In our application both AM335x and PHY would be powered-up at the same time
so it would be difficult to control the AM335x internal pull resistors in software.

So it would be easy for us if we can add external resistor to overcome the internal pull,
could you please let us know if there is any suggestions on the values of external pull resistors
that could be used to overcome internal pulls of AM335x ethernet related pins.
It would be very helpful if there is any reference schematics of AM335x + DP83822 (CPSW mode).

Best Regards
paddu

  • 0
    TI__Mastermind 18425 points
    Hi Paddu,

    Since there are internal pull resistors for both PHY and the processor, it would be difficult for me to directly give you a resistor value. The Internal resistor value for DP83822 strap pins are listed in the datasheet. Some pins have 50kohm pull up resistors and some pins have 9kohm pull down resistors. You will need to check in the AM335X datasheet/reference manual for the internal pull resistors for the processor. Based on the combination of internal resistors of both PHY and Processor, you can select external pull resistors to strap the PHY in the desired mode.
    The target voltage range for each strap mode is listed in table 10 of DP83822I datasheet. Use that table when calculating the external resistor values.

    The recommendation to disable internal pulls of the processor allows to simplify the design by relying on the internal resistors of the PHY.

    -Regards
    Aniruddha