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AM5728: IDK Ethernet connector LED

Colombo Carlo
Mastermind 25525 points

Part Number: AM5728
Other Parts Discussed in Thread: TLK105,

Hi everybody , 

I am on IDK kit  and  have some questions on Ethercat LED  activation :

1--

The COL pin of the PHY (U15, TLK105) is pulled down by 2.2KΩ for setting PHY address to 0x00.

But it seems that in parallel it is connected to the green LED.

According to this I believe that the voltage on this COL pin will be 3.3V - VF (RJ45 LED forward voltage).

Is it enough for resetting the address at power-up (The VIL of the TLK is 0.8V)?

2--

I can see that the green LED is also connected to RXLINK pin.

What is the functionality of this pin?

 

thank you 

regards

Carlo

  • 0
    TI__Guru**** 393215 points
    The factory team have been notified. They will respond here.
  • 0 in reply to Biser Gatchev-XID
    TI__Mastermind 46460 points

    Carlo,

    Please see the following Known Issue from the Appendix at the end of the AM5728 IDK User Guide for an explanation:

    A.18 PHY address LSB for U9 and U15 can be latched incorrectly
    The PHY address LSB for U9 and U15 gets determined by the signal level at the PHY's COL pin during
    reset release. The PHY has a pull-down resistor connected to this pin to enable latching the value of 0.
    Unfortunately, this pin is also connected to one of the RJ-45 connector LEDs that pulls the signal to an
    undefined voltage of about 1.4V during the reset time. Therefore, the PHY address can incorrectly latch a
    value of 1. The LED circuit should be configured for active-high indication and the connections to the LED
    reversed with the cathode connected to ground. This allows the LSB of the address to be properly latched.
    Please refer to Section 6 of the TLK1XX Design and Layout Guide Application Report (SLVA531) for more
    information. The current software workaround programs the RXLINK pin with a pull-down resistor and then
    pulses the PHY reset from a GPIO, to cause it to latch the PHY address correctly.

    Tom