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DP83867CR: Unexpected LED_2 lights up during initialization

Mochi
Genius 4165 points
Part Number: DP83867CR

Hello,

Our customer plan to utilize DP83867 for new design.

Here is concern, when apply following LED driver configuration LED_2 will be turn on during initialization before start data communication. It will be depend on strap voltage setting.

Can we avoid this unexpected LED_2 lights up?

 

Regards,

Mochizuki

  • 0
    TI__Mastermind 39835 points

    Hello,

    It is likely that this is due to the strapping process. If mode 2 configuration is being used, then for the PHY to sample the pin, there will be voltage on the line. If that voltage so happens to activate the BJT which turns on the light, then it is a byproduct of having the strap network.

    Sincerely,

    Gerome 

  • 0 in reply to Gerome Cacho
    Genius 4165 points

    Hello Gerome,

    Thank you for your prompt reply.

    Here is extension of inquietly from the customer.

     

    In the case of mode4 with 1.8V VDDIO, Vmin reach to 1.25V.

    External BJT Vbe will limit the pin voltage at 0.7V, because there is not base resistor,

    Even though this condition, the device correctly identify Mode4 strap voltage?

    Theoretically, may be it difficult. Should we add base resistor?

     

    Regards,

    Mochizuki

  • 0 in reply to Mochi
    TI__Mastermind 39835 points

    Hello,

    If you would like to Mode 4 an LED pin, please look at figure 26 for example circuitry. 

    Sincerely,

    Gerome