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TPS54395: TPS54395 - Operation above 85C Ambient?

Kurt Schmidt
Genius 10945 points
Part Number: TPS54395

I would like to use this device in an application where the ambient temperature is above the maximum data sheet rating of 85C but the actual maximum junction temperature (less than 120C)  will be well bellow the maximum data sheet rating of 150C.

Which data sheet maximum dominates? In other words, are there any reasons (e.g., packaging, bonding, etc.) that would preclude using this device in the above application?

  • 0
    TI__Guru**** 191445 points
    A lot of the parts developed by the old digital consumer power group are specified that way. I looked in the original SCM and there is a pretty much inconsistent data set with regard to temperature. According to the data some specifications are all with respect to Tj not Ta. Many are only for Tj = 25 C. Some parameters are tested at Tj = 85 C, 125 C or 150 C. max. As you can see in the datasheet, the EC table is specified relative to Ta limits, but almost all of the individual line items are limited to Ta = 25 C only and many art "typical" only, so who knows how they will vary over temperature.

    The abs max operating Tj is 150 C. So at Ta > 85 C, you can operate at Tj up to 150 C without violating abs max. Some parameters may be out of spec, but as I said, the datasheet EC values are mostly at Ta = 25 C only or typical anyway. From a practical standpoint all this may be moot anyway. For a typical application Pdiss may be close to 2 W and temperature rise about 80 C. I ran a typical design in webench and for Ta = 30 C, Tj was 110 C. So bottom line is that at Ta above 85 C. the output current will be severely restricted. Also you should be aware that thermal shutdown is 155 C "typical". I would not be surprised if some parts shut down as low as Tj = 140 C (and there is 25 C hysteresis ). I would probably not design for Tj much above 125 C.