TPS54560: compared to Ψjb=23.4℃/W, θjb=23.4℃/W and θJCtop=45.8℃/W

Hirotaka Matsumoto

Part Number: TPS54560

Hi all

Would you mind if we ask TPS54560?

Ψjb=23.4℃/W and θjb=23.4℃/W are the same value.
However, compared to θJCtop=45.8℃/W, there is big difference about value.
So, why is there significant difference?

Kind regards,

Hirotaka Matsumoto

over 8 years ago

0 Hirotaka Matsumoto over 8 years ago

Guru 27585 points

Hi team

If you have some comments, could you let us know?

Kind regards,

Hirotaka Matsumoto

0 JohnTucker over 8 years ago in reply to Hirotaka Matsumoto

TI__Guru**** 191445 points

I am looking into this. It will likely take a few days or more. I am inclined to take the published value as is, but I will let you know if I find anything to the contrary.

0 Hirotaka Matsumoto over 8 years ago in reply to JohnTucker

Guru 27585 points

John san

I am looking into this. It will likely take a few days or more.
->We are waitting for your reply.

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 8 years ago in reply to Hirotaka Matsumoto

Guru 27585 points

John san

If you have some update, could you let us know?

Kind regards,

Hirotaka Matsumoto

0 Hirotaka Matsumoto over 8 years ago in reply to Hirotaka Matsumoto

Guru 27585 points

John san

Could you let us know your circumstance?
Of cource, you don't have the reply, it is no problem.

Kind regards,

Hirotaka Matsumoto

0 JohnTucker over 8 years ago in reply to Hirotaka Matsumoto

TI__Guru**** 191445 points

Just to clarify, your question is:

"Why are theta JB and psi JB equal but theta JC and psi JT greatly different?"

It is because the thermal resistance between junction and top of case is large. For packages with thermal pads, it is assumed that almost all the heat is transferred from the die to the thermal pad thru the low resistance theta JC bottom path. So even though top case temperature is very close to the junction temperature (low psi JT), the actual thermal resistance is still high.

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TPS54560: compared to Ψjb=23.4℃/W, θjb=23.4℃/W and θJCtop=45.8℃/W