Is my buckboost inductor running too hot?

[treez]

Hello,

I am using the coilcraft.com LPS6235 , 10uH inductor in my buckboost design (led driver)

The inductor IRMS = 2.1A
The inductor di = 0.92

Led driver spec

vin = 11.3v
vout = ~33v
iout = 0.
fsw = 926khz
max ambient = 30degc
PCB is potted in tube the size of a thick pen......then outside this its the ambient.

The coilcraft inductor loss calculator says i will dissiapte 522mw total , and get a 64degc temp rise.

Will this be too much?

LPS6235
**broken link removed**

Inductor loss calculator
**broken link removed**

 

[mtwieg]

You need to have some estimate for the thermal impedance of the inductor in the potted tube. Otherwise it's really impossible to say for sure.

But at a glance you are probably pushing that inductor too hard. According to your own numbers it will be saturating slightly, and ones it heats up it will saturate even more. I wouldn't believe any temperature rise numbers the calculator gives, since it doesn't explain how the thermal impedance is derived. Also it says it neglects skin effects, which is pretty absurd.

 

[ccrafter]

Hi,

A 64°C temp rise is too much if you intend to operate at the maximum ambient temperature for the LPS6235 series (85°C). The datasheet shows a current derating curve from which it is evident the max. part temperature is 125°C. If you ambient does not exceed ~60°C it will be ok.

For the small wire used skin effect is not significant as shown by the calculator (AC winding loss is less than 1 mW). Thermal resistance is just the temp rise (40C for the rated current) divided by Irms^2*DCR

Coilcraft always responds quickly to questions so don't hesitate to call or e-mail them with any questions.