LM3481 efficiency drops at higher load HELP please??

Liam Bowman

Other Parts Discussed in Thread: LM3481, CSD18537NQ5A

Hi,

I am currently using the design that was simulated in the WeBench software (attached). I have used every item in the BOM and have taken the LM3481 demo board and have changed it to the components in the design. When I go into the higher loads 100W+ the efficiency drops. Is this because of the diode losses? What can I do to overcome this issue?

over 10 years ago

0 Liam Bowman over 10 years ago

Intellectual 520 points

0 John Bowie over 10 years ago

TI__Intellectual 890 points

Hi Liam, I think the limiting factor maybe your choice of external FET, can you check the specification of the one your using, maybe resize it if required.

regards

John

0 Liam Bowman over 10 years ago in reply to John Bowie

Intellectual 520 points

Hi John,

The current one being used is a BSC042NE7NS3 G Qg=64 nC, Rdson = 4.2mohm(max)

Howard chen suggested:

CSD18537NQ5A: Qg=14 nC, Rdson = 13mohm
BSC100N06LS3 G: Qg = 15nC, Rdson = 10mohm
BSC340N08NS3 G: Qg = 6.8nC, Rdson = 34mohm
Suggestion of a more efficient diode with lowest Vf in our
STPS20M100SG-TR, Vf= 0.455V

I thought that a higher Rds(on) value would make the efficiency worse, why is the Qg being low an important factor?

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LM3481 efficiency drops at higher load HELP please??