• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 379 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DP83822I: LED_1 lights up weakly when reset

Shinichi Inoue
Guru 21626 points
Part Number: DP83822I

Dear Specialists,

My customer is evaluating DP83822I and has a question.

I would be grateful if you could advise.

---

I created a circuit by connecting an LED to the LED_1/GPIO1 terminal.

+3.3V is connected to the anode of the LED, the cathode is connected to a 1kΩ resistorI（RCL）, and the other end of the resistor is connected to the LED_1/GPIO1 terminal.
Since the VF of the LED is about 1.9V, it is calculated that about 1.5mA will flow.

At this time, when the DP83822IRHBR reset (+3.3V is supplied), this LED will light up weakly.

The voltage across the resistor is about 0.4V, and 0.4mA flows through the LED, making it dim.

It seems to be lighting up steadily (the cathode side of the LED was 1.8V and the LED_1/GPIO1 terminal side was 1.4V).

Could you please answer questions below.

①About circuit operation

Could you please tell me the circuit operation that causes the LED to dimly light?

P.7 Table6-1 The LED_1/GPIO1 pin is marked as internal pull-down (S-PD).

On the other hand, the datasheet LED_1/GPIO1 states that it is tri-stated by default.

Which one is correct?


②About the problem

Are there any problems with connection ?

The data sheet says to connect a resistor in parallel.

I wonder if the LED is weakly lit because there is no parallel resistor?


③ pull-up/pull-down values of LED_1/GPIO pin

According to actual measurements, the voltage across RCL is 1.8V/1.4V, and 0.4mA flows.

The internal resistance value of the IC is calculated 1.4V/0.4mA=3.5kΩ. Is it correct?

I would like to know the typical value and deviation %.

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Mastermind 39785 points

    Hi Shinichi,

    So this behavior only occurs when the PHY is held into reset? What happens during normal operation, is this pin acting normally?

    Rp is used to help establish correct polarity in the circuit, especially when the forward voltage of the LED is high to put the pin node in regions near the noise margin specifications.

    Both states are correct, as the S-PD is utilized when PHY is reset while in active mode it can be multiple states with default tri-state.

    Sincerely,
    Gerome

  • 0 in reply to Gerome Cacho
    Guru 21626 points

    Hi Gerome,

    Thank you for your reply.

    I think Rp is necessary to set Mode 4.

    In addition, I'll also ask the customer to confirm the CRS pin settings and register LED CFG1(0x0460) and LED_1/GPIO_1 control(0x0462) settings.  

    When the customer has an additional question, I consult you again.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi