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DP83867IS: Unused pins termination

Oba
Genius 17675 points
Part Number: DP83867IS


Hello

 

I have some questions for unused pins of DP83867IS.

 

Now the below pins are unused pins.

 

TX_D2, TX_D3, GTX_CLK : Interenal PD

JTAG_CLK, TMS, TDI PU : Interenal PU

 

There is some description on the datasheet about unused pins in section 6.1:Unused pins.

I understand additional Pull-up/down is not necessarily required but is good way.

 

What value of register is recommended for this additional external pull-up/down?

Few K ohm is reasonable?

 

I think when adding external pull-up/down, it should be the same direction(up or down) as internal pull up or down.

I checked EVM(DP83867ERGZ EVM), then I found JTAG_CLK is pulled down with 100 ohm.

JTAG_CLK has internal pull-up. Why is this pin strognly pulled down?

 

Is there any pin that have to be specially terminated for unused pins?

 

Regards,

Oba

 

  • 0
    TI__Mastermind 23675 points
    Hi Oba,

    You can add pull-downs or pull-ups in the few k ohm range.
    I do not have a good explanation for why 100 ohm was used. The pin already has an internal pull like you mention, which is sufficient.
    No unused pins have special termination requirements.

    Best regards,
    Ross