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Original question:

DP83867E: Strap configuration and Unused Pins treatment

DP83867E: Purpose of external PU/PD resistors

Ella KIM
Expert 4212 points
Part Number: DP83867E

Hi expert,

I'd like to ask for your help to understand the PU/PD configuration. As per the related thread :

Device has internal PU/PD of 9k , hence can be left floating. However if you want to be have extra safety on design, you can always have external PU/PD. Hope this is clear. You can use PU/PD thru 2.2K resistor.

1. Could you kindly give me more information why external 2.2k of PU/PD resistor adds extra safety on design? I wonder why the device requires the external PU/PD resistor even though the device itself already internally support it.

2. Additionally, I'm going to use 10kohm PU resistor on INT/PWDN pin and RESET_N pin instead of 2.2k which is recommended in DS. Could you advise the possible effect here?

Thank you for your help!

  • +1
    TI__Genius 17260 points

    Hi Ella,

    For your first question, this section highlights adding a pull-up or pull-down to strongly tie the pin to gnd or vddio. Let's say that the default pin has weak 9k pull-up and there is a connected device that has its own internal PD, the strong external pull-up will negate any contention, adding extra safety.

    For your second question, the recommended values ensure logic high. The change you mentioned on the INT/PWDN pin to a 10k should be okay as long as vih voh levels are reached.

    Kind Regards,

    Joe

    All information in this correspondence and in any related correspondence is provided “AS IS” and “with all faults”, and it is subject to TI’s Important Notice (www.ti.com/.../important-notice.shtml).