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DP83826I: Tj spec confirmation

Allen Lu
Intellectual 2130 points
Part Number: DP83826I
Other Parts Discussed in Thread: DP83826E

Hi team:

 As check with the D/S via TI.com. it did mentioned about the Tj spec, but i found the answer via e2e as below reply: Max recommended Tj for the DP83826 is 110°C for the E version and 90°C for the I version.

 But there are something want to double confirm is that the ambient temperature of I version can reach 85 degrees Celsius. Why is the T junction temperature only so low as 90 degrees Celsius? According to the thermal resistance of 52°C/W and the power consumption of 45mA & 0.148W, at an ambient temperature of 85°C, the junction temperature has exceeded 90°C, which is inconsistent with the specification that it can be used at an ambient temperature of 85°C.  

 Your comments will be very appreciate.

 BTW, why the DP83826E and I version have such a big temperature difference? DIE reason or design margin?

  • 0
    TI__Mastermind 36830 points

    Hello,

    Thank you for your query. We are checking with the internal teams on this, but as there is holiday, please expect delays in response. I will look to update at latest EoD 11/2.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 2130 points

    Hi Gerome:

     Tks for the comments, your reply is really appreciate .

  • 0 in reply to Allen Lu
    TI__Mastermind 36830 points

    Hi Allen,

    After checking with the team, there are wide amounts of literature regarding thermal resistance calculations. The most relevant to you:

    - Theta_J_A is used to compare between devices, but not for actual temperature calculations

    - PSI_J_T is used for application calculations, using formula Tj = Tc + PSI_J_T * Sigma_Power. Tc is the temperature of the case top where customer would physically measure using a thermocouple.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 2130 points

    Hi Gerome:

     tks for the comments, but as i check, when we work at 85C°， using formula Tj = Tc + PSI_J_C * Sigma_Power = 85 + 42 *（3.3V*0.045mA)=85+6.237=91.237 > 90°C for the I version.

    Does it exceed the specification requirements?

  • 0 in reply to Allen Lu
    TI__Mastermind 36830 points

    My apologies Allen, it was not PSI_J_C, but PSI_J_T. I have corrected my previous post to correct this typo. This would add .14C above the case temperature.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Intellectual 2130 points

    Noted,

     so Tj = Tc + YJT * Sigma_Power = 85 + 2.1 *（3.3V*0.045mA)=85+0.311=85.311, am i correct?

     but weird is that how the .14C comes?

    Gerome Cacho said:
    add .14C above the case temperature.
  • +1 in reply to Allen Lu
    TI__Mastermind 36830 points

    Hi Allen,

    The .14C comes from a total power contribution of 67mA maximum between VDDA/VDDIO at 3.3V. This would be added onto the measured temperature of the top of the IC from using a thermocouple.

    Sincerely,
    Gerome