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Webench/LM3424: LM3424/LM3424BKBSTEVAL Thermal problem with MOSFETS driving 8 LED's @ 3A

Mario Jimenez
Prodigy 200 points
Part Number: LM3424

Tool/software: Webench

Hello,

I want to use the LM3424 to drive 8 LED's @ 3Amps (Cree® XP-L2, 8x2 series-parallel arrangement)with a 24V battery. I bought the LM3424BKBSTEVAL, which already gives 1A output.

I tried an alternate design provided on datasheet (AN-1967), which gives 2.5A output. It indeed worked, but the PCB, MOSFET's(Q1) and main diode (D1) gets hot as hell.

I ran webench but it couldn't suggest a part number for Q1.

I already changed the inductor and diode to a bigger ones, but Q1 keeps getting hot with barely 5 seconds on. I even tried two power mosfets in parallel. I changed Q1 to IRFP048NPBF,  IRFS4115TRLPBF, but both had the same problem.

I also attach my LED array:

8484.SIN000065-01_Helios_2x8_SCH.PDF

Could you suggest me some power mosfets to use in my design? Some thermal dissipation tips/ layout guidance with copper area would be useful too.

Thanks.