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LM3481 The method of calculating the junction temperature from the actual temperature measurement

Tomoaki Yoshida
Expert 2200 points

Hi,

My customer will measure the case temperature actual boards that are designed, they want to estimate as accurately as possible junction temperature.

Since the board condition is different, they're thinking θia in datasheet is different from their design.

They try to estimate Tj as follows using θ jc.

Tj＝Tc＋Pd(worst)＊θjc

Pd(worst)＝Vin(Max)×（Ｉsupply＋fsw×Qg）

Is it no problem by idea like the above?

Please tell me, if there is a way to make an estimate more correctly.

Best regards,

Tomoaki Yoshida

  • 0
    TI__Genius 13700 points
    Hello,

    While there might be some variation the parameters that define the thermal resistance between the junction and the case are not influenced by the design.

    Have you had a chance to review the document referenced in the datasheet about applying thermal metrics correctly? Here is a link. It is a pretty good read.
    www.ti.com/.../spra953b.pdf


    If you can get a thermal image or a temperature sample from the top of the case of the device you should be able to estimate the junction temperature with relative accuracy seeing as thermal resistance between the junction and the top of the case is defined in the datasheet. You would want to use the RθJC(top) parameter. Read section 3 of the linked document above to properly determine the junction temperature for the temperature of the top of the case.