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TPS7A26: TPS7A26 thermal simulation

Masaharu Takahashi
Expert 4170 points
Part Number: TPS7A26
Other Parts Discussed in Thread: LM317

Hi, Team.

Could you simulate how much thermal would be with below condition?

・Vin：12.7±4％

・Vout：5.0V

・Iout：250mA

・ambient temp：70℃

as my calc, (12.7-5)*0.25*73.3=141℃+ 70℃=211℃

Customer wants to know how much is the thermal resistance and how much thermal IC generates with specific soldering coverage from -% ~ 100% to know how much they need to make soldering at least.

could you show the graph which shows the thermal resistance from 0% ~ 100% soldering coverage on its flip side ?

  • 0
    TI__Guru 50190 points

    HI Takahashi-san,

    Your calculations are correct. Here is a very good application note showing how different layouts can affect thermal performance.

    I hope this answers your question.

    Regards,

  • 0 in reply to JCHK
    TI__Expert 4170 points

    Hi, John-san.

    what customer expects us is to simulate how much temperature raises.

    could you please ?

  • 0 in reply to Masaharu Takahashi
    TI__Guru 50190 points

    HI Takahashi-san,

    Any thermal simulation would need to be based on their specific layout. Our TJA comes from simulation based on a JEDEC standard High-K board. While this is clearly an impractical layout, you can see from Gerard-san's application note, a good layout could actually have slightly better thermal results. 

    It would not be easy for any Linear Regulator to sustain a 7.7V drop at 250mA. Even with a TO-220 package (i.e. LM317) you are looking at 7.7*0.25* with a TJA of ~30C/W we have 7.7*.25*33.5+70=134.5C  which would be over the recommended maximum junction temperature. 

    Is the 250mA maximum or nominal current?

    Please let me know.


    Regards,

  • 0 in reply to JCHK
    TI__Expert 4170 points

    hi, John-san.

    Is the 250mA maximum or nominal current?

    ->constant is 250mA and its max is 500mA.

  • 0 in reply to Masaharu Takahashi
    TI__Guru 50190 points

    HI Takahashi-san,

    A linear regulator supporting a 7.7V drop at 500mA (3.85W) is thermally very difficult.  Normally at these high VIN-VOUT and load currents, a buck converter is used to pre-regulate the input for an LDO which are optimized for smaller VIN-VOUT differentials. 

    I hope this helps.