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66AK2G12: how estimate junction temperature in early stage?

Part Number: 66AK2G12

On behalf of customer:

 

Dear,

May I have your advice how do I estimate junction temperature in early stage as following?

 

Device: 66AK2G12

 

I have read/checked spra953c.pdf, sbva025.pdf, sprabi3b.pdf, or some e2e, but I cannot decipher enough how I should estimate Junction temperature(Tjunction) in early stage.

Early stage mean I can have ambient temperature(Tambient) from previous product that not uses TI processor, while I will use TI processor for next product.

Therefore I don’t have case temperature(Tcase) for TI processor, even though the Tcase should be used in following equation:

 

Tjunction = Tcase + (ψjt x Power)  (from spra953c.pdf, page8, equation(8))

 

While I know also there is following equation, but as spra953c.pdf mention that usage of “Rθja” is misapplication.

 

Tjunction = Tambient + (Rθja x Power)  (from spra953c.pdf, page2, equation(1))

 

Question:

Should I use following equation when I have Tambient and don’t have Tcase?  Or is there another suitable equation/way when I have Tambient, don't have Tcase?

Tjunction = Tambient + (Rθja x Power)  (from spra953c.pdf, page2, equation(1))

 

I’m sorry if I overlook something, but may I have your advice?

 

Best regards,
Gou

 

  • Hi Gou,

    Question:

    Should I use following equation when I have Tambient and don’t have Tcase? Or is there another suitable equation/way when I have Tambient, don't have Tcase?

    Tjunction = Tambient + (Rθja x Power) (from spra953c.pdf, page2, equation(1))



    I’m sorry if I overlook something, but may I have your advice?


    My understanding is that you should follow www.ti.com/.../spra953c.pdf & www.ti.com/.../sprabi3b.pdf. That is use the above mentioned equation. However, you should take into account Table 1. Factors Affecting RθJA for a Given Package Outline from SPRA953.c. You should also consider Section 5.8 Thermal Resistance Characteristics for ABY Package from the device Datasheet, where RθJA is measured.

    I am also looping the design team to elaborate if necessary.

    Best Regards,
    Yordan
  • Hi Yordan,

    Thank you very much for your reply.  May I have your double-check for following?

    Current my customer would like to estimate with Tabmient=55℃, if this condition, should we estimate as following?  So far my customer estimate 2.631W for power consumption for 66AK2G12.

    Tjunction = Tambinet + (Rθja x Power) = 55 + (14.2 x 2.631) = 92.36℃

    I’d like to know above formula makes sense for us.  Because note (1) in “5.8 Thermal Resistance Characteristics for ABY Package from the device Datasheet” says following,

    These values were derived from thermal simulation using 1W of power dissipation and ambient temperature of 25

    Of course, we should consider above formula don’t consider power dissipation from PCB or other, that mentioned in spra953c.pdf

    I’d like to know above 92.36 is over-estimation or reasonable or under-estimation.

    Best regards,

    Gou

  • Hi,

    The calculation is correct. I am not sure about Rθja, which as stated is calculated for ambient temperature of 25 degrees Celsius.
    I've consulted the design team to elaborate on this. We'll get back with any feedback we have.

    Best Regards,
    Yordan
  • Hi,
    Thank you very much for your reply.

    Best regards,
    Gou