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DP83822I: Could you tell me how to configure LED_0?

Kazuya Nakai59
Guru 21595 points
Part Number: DP83822I

 One of my customers is drawing PCB schematic to design their own PCB to evaluate DP83822.

 Then they got the following questions. Could you please tell me your answers?

Q1. Is LED_0 pin a strap pin? (I think it is yes because the LED_0 is described in Table11-4level strap pins)

Q2. Is LED_1 pin a strap pin? (I think it is no.)

Q3. Is LED_0 and LED_1 active level set by Rp (pull-down or pull-up resistor) automatically? (I think it is yes.)

Q4. If LED_0 is a strap pin and we want to set LED_0 pin to low active (LED ON: LED_0 pin level = Low),

      how are strap pin setting resistors, LED current series resistor and LED_0 pull-up resistor for low active

      setting connected?

 Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.   

  • 0
    TI__Mastermind 23675 points
    Hi Kazuya-san,

    You are correct that LED_0 and LED_1 are both strap pins with internal pulls.
    For LED_0 to be an active LOW you need to set the pin with an external pull-up resistor.
    The PHY will detect the HIGH on that pin during power-up/reset.

    Please add a pull-up resistor in parallel to your LED and current limiting resistor.
    This will ensure that you are strapping to MODE 4 state.
  • 0 in reply to Ross Pimentel
    Guru 21595 points
    Hi Ross,

    Thank you for your reply.

    Could I ask you a few additional questions as the follows?

    Q1. How should external resistors be connected when LED_0 is set to MODE0 and low actve?
    Table9 on page 47 says that RH=open and RL=1.96kohm should be connected for MODE0 setting.
    But in the case, I think LED_0 will be set to high active mode.

    Q2. The following E2E reply said that LED_1 is not a strap pin. You said LED_1 was a strap pin.
    e2e.ti.com/.../560419

    Which is correct?

    Thank you and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 23675 points

    Hi Kazuya-san,

    A1) If you use that method, you will be sinking current even in a non-illuminated state (because of the pull-down) are you sure you want that?

    What you have to do is override the polarity automatically set using register 0x18 bit[7].

    A2) It is a strap pin, but the pin is for internal use only. This is why the pin must be strapped to either MODE1 or MODE4. MODE2 and MODE3 are not allowed.

  • 0 in reply to Ross Pimentel
    Guru 21595 points
    Hi Ross,

    Could I have your help again?

    1. I think both bit 7 of 0x0018 LED Control Resiter(LEDCR) and pull up/down resistor setting as Figure 31 can be used for LED_0 polarity setting, . Is this correct?

    2. Do you mean that the bit 7 setting of 0x0018 LED Control Resiter(LEDCR) is high priority than the pull up/down resistor setting?

    Thank you very much and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 23675 points
    Hi Kazuya-san,

    A1) Register setting will determine polarity at power-up and reset. This can be overridden through register access using bit[7].

    A2) Bit[7] is the result of the bootstrap on the LED pin, but this value can be overridden and forced to a different polarity.
  • 0 in reply to Ross Pimentel
    Guru 21595 points
    Hi Ross,

    Thank you for a lot of your supports.

    Best regards,
    Kazuya Nakai.