• Resolved

hi, TI

If developers measure the case temperature and the board temperature,
do they obtain the junction temperature from the equation below?

Thanks and Best Regards,

OHTA

• OHTA:

The equations did not come through the post. Regardless, you can calculate the junction temp by:

Tj [degC] = Tc [degC] + theta-jc [degC/W] * Pdiss [W].

Alternatively you can substitute board temp and theta-jb.

--RJH
• In reply to RJ Hopper:

Hi, RJH

I confirmed SPRA953C”Semiconductor and IC Package Thermal Metrics”.

It says that the equation(Equation 4) is invalid.

Also, SPRA953C says that Ψjt should not be used when application of a heat sink is intended. Instead, Equation 5 and Equation 6 should be used.

but, I cannot measure θsa. so, I cannot calculate the junction temp by Equation 5 or Equation 6.

For that reason, I deduced that equation( I thought that equation with the idea of a two-resistance model)

which equation should I use for calculating correct junction temperature?

• In reply to RJ Hopper:

hi, RJ Hopper

sorry, I did not notice that the equations did not come through the post.

I have attached files(the equation and Equation4~6 of spra953c)

Thank you and Best regards

OHTA

spra953c says that Equation 4 is invaild.
Because, a very small percentage of heat energy in a typical plastic package is convected and radiated off the top surface of the package.
so, I deduced the equation with the idea of two-resistance model.

OHTA
• In reply to RJ Hopper:

Spra953c says that Equation 4 is invaild.

Because, a very small percentage of heat energy in a typical plastic package is convected and radiated off the top surface of the package.

Tj [degC] = Tc [degC] + theta-jc [degC/W] * Pdiss [W] _______Equation 4

So, I deduced a equation below with the idea of two-resistance model.

Is the equation below correct?