Hi,
I'm doing a new board based on the LM3410, basically the LM3410X SEPIC demo board, I'd like to shrink it a little too so I want to make sure I'm understanding the power dissipation paths.
LEDs
LED Vvf = 3V and I = 0.35A. I'll do a string of 8 which is 24V @ 0.35A
That makes output power 8.4W
Input Power
My input will be 5V. I don't know the efficiency but if it was a magically 100% that would mean I needed an input current of 1.68A.
Power Dissipation by LM3410
The LM3410 has a Rdson of 0.33 Ohm so at 1.68A that's 0.93Watts (way more than the SOT package can handle). I assume I'll have to do a little thermal simulation here and use the LM3410XMFX with the DAP.
Inductors
I think L1 takes the worst of it. The Coilcrafts you use have a 0.043Ohm DCR, but even at 1.5x the input current of 1.68A that's 0.273W. L2 I think only takes the load current so that would be 0.35A ^2 * 0.043 = 5mW.
Catch Diode
The catch diode from your design has a Vfw of 0.32 so at 0.35A load current that's 112mW dissipation.
Am I on the right track here despite not calculating the efficiency? Did I miss anything important? Also it looks like the SoT part is a no-go because it has a 400mW maximum power dissipation, and I assume the smaller parts power dissipation will be dependent on the size of GND plane I attach it to (and air flow etc.).
Thanks!
