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DP83848Q-Q1: About RBIS pin

Tomoaki Yoshida91
Genius 5255 points
Part Number: DP83848Q-Q1

Hi team,

I have some qustions about RBIAS pin.

Our customer designed the board mounted DP83848Q-Q1.

The boards were assembled, but with mistake it was supposed to connect a resistor of 4.87 kΩ to the RBIAS pin, but 20 Ω was mounted.

At this time, turning on the power will cause a large current to flow through the device, causing large heat generation?

They say that the device got very hot.

Could you explain the function of the RBIAS pin and why it should be connected to GND 4.87 kΩ?

Best regards,

Tomoaki Yoshida

  • 0
    TI__Mastermind 18425 points
    Hello Yoshida-san,

    RBIAS resistor is a critical design requirement and is used by the IC to set the correct biasing for internal blocks. It should be 4.87kohm 1% tolerance resistor. 20Ω is too low and should be changed to 4.87kΩ 1% tolerance resistor.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Genius 5255 points
    Hi Aniruddha-san,

    Thank you for your reply.
    Yes, they should switch to the correct 4.87 kΩ as soon as possible.

    In the case of 20 Ω by mistake, the IC became very hot.
    Is this possible?

    We can think that the problem that IC becomes hot is solved if we know the reason that large current flows when RBIAS pin is connencted 20 Ω.


    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida91
    Genius 5255 points
    Hi Aniruddha-san,

    Is there any update?
    Our customers may have caused the device to heat up and be broken by mistaking the resistance of RBIAS.
    They are considering reworking chips, but they would like to confirm in advance that the cause of device heat generationr is RBIAS.

    In the case of normal 4.87 kΩ, how much current flows to the RBIAS pin?
    If it is mistakenly attached 20 Ω, how much the current?

    Best regards,
    Tomoaki Yoshida
  • 0 in reply to Tomoaki Yoshida91
    TI__Mastermind 18425 points
    Hello Yoshida-san,

    We do not characterize the current flowing through RBIAS pin. For our validation, we connected the 4.87kohm resistors in the circuit and perform all our testing using that value. It is highly likely that the large heat dissipation is due to incorrect RBIAS value. Kindly ask the customer to make the change to the correct RBIAS value and test again.

    -Regards,
    Aniruddha