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
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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
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