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TPS703: TPS70302 Junction temperature

Dong Ba
Intellectual 1055 points
Part Number: TPS703

Hi Team,

The customer use TPS70302 @85°C, and Tj=Ta+RθJA*Power=85+40=125 or some more. But when looking up Tj in the datasheet, it gives 2 different value. 

I understand the upper Tj is a mistake, it shall be Ta. If Tj=150, I think the customer can use this chip . If Tj=125, do you have any recommendation.

Thanks,

Eric

  • 0
    TI__Mastermind 37065 points

    Hi Ba,

    The maximum junction temperature is 150C, which is where the nominal thermal limit protection kicks in.  As this will have some variation, it is possible that thermal limit protection will engage a little below 150C.

    How is the customer determining their Tja and rise in temperature?  There is plenty of information in the datasheet starting on page 22, but as the application specific Tja is heavily dependent on the board layout, I want to be certain there is an issue here.  A great way to determine the customers actual Tja is described in the second app note link below.  If the customer still has an issue after reviewing their board specific Tja, we can discuss alternatives but they will likely be in a different package as this package is not heavily used for most of our devices.

    An empirical analysis of the impact of board layout on LDO thermal performance

    https://www.ti.com/lit/an/slvae85/slvae85.pdf

    Measuring the Thermal Impedance of LDOs in Situ

    https://www.ti.com/lit/an/slva422/slva422.pdf

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1055 points

    Hi Stephen,

    Nice to get your feedback. I would transfer the useful information to the customer.

    Further more question. You Mean Tja=Ta (ambient temperature) right? The customer's working environment is Ta=85°C. About temperature rise, the customer just follow RθJA in the datasheet and Power measurement. 

    And The maximum junction temperature is 150C as we confirmed, assumed that the customer get the right RθJA according to your method above, when Tj=Ta+RθJA*Power=85+40=125 or more but less than 150, so in this case the customer still can use this chip, right? 

    B.R.

    Eric

  • 0 in reply to Dong Ba
    TI__Mastermind 37065 points

    Hi Eric,

    By Tja I mean junction to ambient temperature, not Ta which is the ambient temperature.  By following the thermal resistance RθJA in the datasheet, the customer may be over estimating their thermal rise.  The apps notes I linked to previously will be very helpful in determining if the customer will experience as large of a rise in temperature as the datasheet RθJA would suggest.

    The temperature limit protection circuitry kicks in at nominal 150C, but there is tolerance to this just like everything. So it may kick in below 150C but the linear regulator will operate up to 125C without issues. 

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1055 points

    Hi Stephen,

    Thanks for the kind help. 

    -I got your point about RθJA. For Tja, we know Ta or Tj, You Mean Tja=Tj-Ta=RθJA*Power right?  If not, please help to provide more explanation about this, it is hard to understand "junction to ambient temperature".

    -"The temperature limit protection circuitry kicks in at nominal 150C, but there is tolerance to this just like everything. So it may kick in below 150C but the linear regulator will operate up to 125C without issues. "

    You mean, for this part, it is better to use below this value Tj=Ta+RθJA*Power=125, Right?

    B.R.

    Eric

  • 0 in reply to Dong Ba
    TI__Mastermind 18466 points

    Hi Eric, 

    Yes, you are correct about Tja and about operating under 125 to keep predictable behavior on the LDO. 

    Best,

    Juliette