TPS63031: TPS63031 Operation at 125C ambient

Hi Frank,

It is not recommended to operate the device at Ta 125 degC, because that is already the recommended Tj:
If you have 125 degC already on your board (if, as you are assuming, absurdly your board is made of a super thermal conductive material), and the device is off, that would be your Tj as well. When you turn it on, Tj will rise above it, even with no load condition, because of the Junction-to-board thermal resistance.

Talking about your calculation in genaral, it seems your max current is the one to reach the abs max temperature. I would use margin from it.
Most importantly this max current you calculated is not correct because you used the wrong parameter. You need to take into account the Junction-to-board AND board-to-ambient thermal resistances, which depends on the board material, pads and layout. Plus you need to consider the heat transferred form the other devices on the board, if there are.

I suggest you to read our appliucation not about the meaning and use of the thermal parameter you find on our datasheet:
www.ti.com/.../spra953c.pdf

Best regards,
Emmanuel

Yes, I understand what is being recommended, but I'm trying to push the envelope to the Absolute maximum specs, (beyond what is recommended, but not beyond the Absolute max)

So what does "Operating virtual junction temperature, Tj 150C" mean? (Not defined in the paper you reference), and how does that differ from absolute max Tj?

Yes, assuming everything is heat soaked at 125C and you turn it on, then there will be additional heat generation at the junction, the question is how much current can you pull at 125C to make the junction stay at or below 150C, of course you always provide margins when doing any design, but you want to know the max.