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DP83848I: Max. recomended junction temperature

Daniel Gregor
Prodigy 90 points
Part Number: DP83848I

Hello,

we are using the DP3848I in extreme temperature conditions. The housing of the PCB is very small and the ambient temperature measurement is not representative in this case. So we have decided to measure the case temperature und calculate the junction temperature. Tj = Tc + Rjc*P  (Rjc=30,9°C/W, P=0,267W).

The chip is used in an industrial application where a lifetime of 10years is required. What is the recommended maximum junction temperature?

  • 0
    TI__Mastermind 18425 points
    Hi Daniel,

    Junction temperature is not characterized in the datasheet so it would be difficult to provide a number. As long as the ambient temperature stays within the operating range of the PHY then it should be ok. Is there a way for your to check the ambient temperature in the housing?

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 90 points

    Hi,

    in our case it is very difficult to measure a representative ambient temperature. In the housing, where the PCB is placed, we have a lot of heating sources and a very large temperature gradients. Hence it is very difficult to measure the “real” ambient temperature. This is the reason why we decided to measure the case temperature of the ICs and calculate the junction temperature.

    We also have an STM32F407 on the board. The maximum junction temperature is 125°C. The operating junction temperature is only 105°C.

    Do you think , we can proceed in the same way with the DP83848I? This means 105°C for the operating junction temperature? Tcmax= 105°C-(0,267W*30,9W/K)=96,7°C

     Regards,

    Daniel

  • 0 in reply to Daniel Gregor
    TI__Mastermind 18425 points
    Hi Daniel,

    Using the junction to ambient coefficient, we can estimate that the junction temperature at 85C and max power is around 105C. You can use this to calculate the case top temperature. You equation above seems correct. However, since this is not a datasheet parameter we can only provide estimates and this cannot be guaranteed.

    -Regards,
    Aniruddha