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DP83826E: DP83826E LED Configuration

Yang Wu
Expert 3170 points
Part Number: DP83826E

Hi Team,

I have a question on the LED configuration for the basic mode. The DS says if strap selecting 0, a 1 kΩ pull-up resistor in series with the LED should be used and a 5 kΩ pull-down resistor. does there still need the 1.5KkΩ pull-down resistor to be parallel with the 5kΩ resistor?

In addition, since the the LED polarity will always be active low, does it means the LED will be always ON (because it's pulled up to 3.3V)? thanks a lot.

Best regards,

Yang

  • 0
    TI__Mastermind 37380 points

    Hi Yang,

    The 1.5k PD for the LED is required as this helps bias the voltage at strap sampling if intending to turn a default PU pin low. 

    For polarity, as this will be a low strap, this would be active high due to auto-polarity detection and correction.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Expert 3170 points

    Hi Gerome,

    thanks for your reply. But I am confused here, the DS says basic mode doesn't have auto-polarity detection, right? if it doesn't have, I think the LED will be always ON. thanks.

    Best regards,

    Yang

  • 0 in reply to Yang Wu
    TI__Mastermind 37380 points

    Yang,

    My apologies. Basic mode does not have polarity detection/correction and is active low. The datasheet has a typo, and the PD value should be 1.5k, not 5k. The LED should be connected to VCC for proper operation of active low LED polarity.

    Sincerely,

    Gerome