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DP83822I: Disturbances on LED 1 pin

Anders Wikström
Prodigy 60 points
Part Number: DP83822I

Tool/software:

Hi,

I have found a strange problem that I can't totally explain. The PHY does not answer on the MDIO interface.

Everything seemed to be correct (power, bootstrap, power-up, signal integrity and so on), however pin "LED_1/GPIO1" and "LED_0" are both connected with a 22k resistor to  LEDs. The LEDs could of course not light up due to the low current(high resistor value).

For pin "LED_1/GPIO1" this also contributed to the main problem. When removing the LED (D68) connected on this pin or lowering the resistor to a more reasonable value(~500Ohm), the chip starts to respond on the MDIO interface.

For pin LED_0, regardless of the connection, the chip worked(except for the LED).

Can you find some kind of explanation for this? I'm guessing that the ~30uA flowing through the LED on pin "LED1" is somehow disturbing the chip. This pin must also be more sensitive since the same configuration on LED_0 does not have the any affect on the chip.

Looking forward into getting more clarity to the root cause here.

Br

Anders

  • 0
    TI__Genius 15696 points

    Hi Anders,

    What is the purpose of having the 22kΩ resistor in the first place if the LED will never turn on? My first guess would be that LED1 is getting strapped into Mode 2/3, which are not recommended for use. 

    Regards,

    Alvaro

  • +1 in reply to Alvaro (Al-vuh-roe) Reyes
    Prodigy 60 points

    Hi,

    No purpose, the resistor value is wrong. In my version of the datasheet LED_1 is not a bootstrap option?

    Edit: I had an old version of the datasheet..

    Measuring the LED_1 pin during reset since it is also a bootpin showed a voltage of ~0.45V. The reason LED_0 does not contribute to this problem since it has an internal PU during reset and LED_1 a PD.

    Thanks for the input!

    Br

    Anders