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DP83826E: Pull-up, Pull-down resistor value for bootstraps

?? ??
Prodigy 60 points
Part Number: DP83826E

Tool/software:

I have a question regarding the values of pull-up and pull-down resistors for bootstraps in the TI_DP83826E.

The datasheet recommends a pull-up resistor value of 2.49kΩ and a pull-down resistor value of 1.5kΩ.

It is also stated that the recommended tolerance is 1%.

On the other hand, the bootstrap has two levels, with VH minimum at 1.3V and VL maximum at 0.6V.

The internal pull-up and pull-down resistor values are both 10kΩ ±25%.

Considering the threshold values and internal resistor values, is it acceptable to use pull-up and pull-down resistor values other than 2.49kΩ and 1.5kΩ for bootstraps?

Why is a 1% tolerance recommended?

  • 0
    TI__Expert 5200 points

    Hi, 

    ?? ?? said:

    Considering the threshold values and internal resistor values, is it acceptable to use pull-up and pull-down resistor values other than 2.49kΩ and 1.5kΩ for bootstraps?

    As you mentioned, the internal pull-up resistor has a rather large tolerance. The TI recommended values have a low tolerance (1%) to make sure that in the worst-case scenarios involving the internal PU, as well as the operating temperature range, the device functions properly. These particular values have been tested across the temperature range of the device and ensures that the device reads the correct strap values.

    While other resistor values may be used, it is good practice to do the appropriate calculations to make sure that the voltage requirement at the pin will be met.

    Best,

    Vivaan

  • 0 in reply to Vivaan Jaiswal
    Prodigy 60 points

    Hi Vivvan

    Thank you for your reply.

    For a 3.3V power supply (with a variation of ±5%), the pull-up resistor is 5.1kΩ (±5%), and the pull-down resistor is 1.3kΩ (±5%), resulting in Vh being below 0.47V and Vl being above 1.82V.

    I believe this should be acceptable, but is there any issue with this?

  • +1 in reply to ?? ??
    TI__Expert 5200 points

    Hi, 

    As long as every corner case of your system meets the voltage requirements listed below at the PHY pins, the device should function as expected. Note: The internal PU resistor should also be included in the calculating the voltage

    Best,

    Vivaan