i.MX6DQ Junction to Case.

[satoshishimoda]

Hi community,

I have a question about i.MX6DQ thermal resistance.

Please see Table 5 in IMC6DQCEC Rev.3.

I understand junction temperature is present by the following equation.

"Junction to Case" (< 0.1) = ("Junction Temperature" - "Case Temperature") / "Power consumption" : [equation 1]

=> "Junction Temp" = "Junction to Case" / "Power consumption" + "Case Temp" : [equation 2]

Then, should I assign "0.1" to "Junction to Case" in equation 2 to calculate "Junction Temp"?

Or can I think "Junction Temp" = "Case Temp" because "Junction to Case" is small value sufficiently?

Best Regards,

Satoshi Shimoda

[Yuri]

Generally You are right. But please note, Theta-JC parameter is suitable for estimations

during heat sink selection, since it is measured by the cold plate method.

Please look at side 83 (Appendix D, Heat Sink Selection) of AN4579 “i.MX 6 Series Thermal

Management Guidelines”

http://cache.freescale.com/files/32bit/doc/app_note/AN4579.pdf

Have a great day,
Yuri

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[satoshishimoda]

Hi Yuri,

> Generally You are right. But please note,

Excuse me, did you said which my understanding is correct?

> Then, should I assign "0.1" to "Junction to Case" in equation 2 to calculate "Junction Temp"?

> Or can I think "Junction Temp" = "Case Temp" because "Junction to Case" is small value sufficiently?

Best Regards,

Satoshi Shimoda

[Yuri]

Please look at my comments below.

1.
> Excuse me, did you said which my understanding is correct?

Yes.

2.
> Then, should I assign "0.1" to "Junction to Case" in equation 2 to calculate "Junction Temp"?

> Or can I think "Junction Temp" = "Case Temp" because "Junction to Case" is small value sufficiently?

You may apply any mentioned approach.

3.

Again, I would like to emphasize the point, that Theta-JC parameter is used in context of thermal model,

mentioned in the side 83.

[satoshishimoda]

Hi Yuri,

Sorry, I have not understood yet.

> 3.

> Again, I would like to emphasize the point, that Theta-JC parameter is used in context of thermal model,

> mentioned in the side 83.

OK, I should use this equation to calculate Tj.

Then, which value (0 or 0.1) should I assign to R theta-JC?

Best Regards,

Satoshi Shimoda

[Yuri · Accepted solution]

For assurance, please use R theta-JC = 0.1 , especially when thermal estimations are provided for

board, that should work under "hot" environment; when the results of the calculations violate the design

requirments (if the resulting junction temperature is more than 105'C). In these case, you might use special

CFD software (e.g. FloTHERM) to make thermal analysis.