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TPS54325 TA vs Output current Data

Genius 4155 points
Other Parts Discussed in Thread: TPS54525, TPS54325

Hi,

Does anyone have the "OUTPUT CURRENT vs AMBIENT TEMPERATURE" graph

same as in TPS54525 D/S page12 figure13 ?

If not, Would it be possible to make the graph for TPS54325?

Thanks

Go

  • For TPS54325, the graph is not needed.  TPS54325 can support 3 A output for the entire operating ambient temperature range of -40 to +85 C on a well designed pcb.  So essentially the graph would just be a straight line at 3 A.

  • Hi, John

    Thank you for your comment.

    I tried doing the WEBENCH simulation for TPS54325 under the following conditions.

    (Vin=12V , Vout=3.3V , Iout =3A , TA=85℃)

    but I couldn't do that due to the over junction temp. 

    In TPS54325 D/S, THETA-ja=55.6℃/W with High-K board.

    so we need over 90% efficiency under the condition that described above.

    Is it really possible to support 3A output current for a general assumed conditions like that?

    Thanks

    Go

  • can you post your exact inputs to webench?  I'll see if I can duplicate it.

  • Hi, John

    Here is the info about WEBENCH simulation that I did.

    please see the attached file.

    Thanks

    Go 

    Webench Simulation result.pptx
  • I'll see what i can find out.  it may take a few days.

  • I checked this circuit on the bench.  To summarize the webench results:

    Theta JA = 55.6 C/W (JEDEC standard coupon)

    Pdiss = 1.34 W

    Ta = 30 C

    Tj = 30 + 1.34 * 55.6 = 104.5 (webench actually calculated 105.6 C, probably some rounding error)

    Bench result, Vin = 11.98 V, Iin = 0.956 , Vout = 3.327 V, Iout = 3.00 A

    T top of case = 52 C.

    Ta = 25 C

    Pdiss (minus inductor conduction loss) = 1.3 W (pretty close to the calculated webench Pdiss1.34 W)

    Tj = Tc + psi JT*Pdiss = 52 + 1.8 * 1.3 = 54.34C.

    T rise = 54.34- 25 = 29.34

    Theta JA for EVM = 22.57 C/W

    So the actual EVM thermal performance is better than 2 x the JEDEC coupon.  JEDEC coupon results are really more for comparison purposes rather than actual results.  It allows devices to be compared using identical standard conditions.  For a well designed PCB, the TPS54325 should be able to deliver full output up to Ta = 102.4 C, well above the recommended operating temp of 85 C