LM5146: No load current

NIcolas Gallardo

Prodigy 40 points

Part Number: LM5146
Other Parts Discussed in Thread: LM5145, CSD19534Q5A

Tool/software:

I've implemented the below circuit with the following specs:

1. Input voltage: 43V-58V

2. Output voltage: 24V

3. Max Current Output: 8A

When connected to a benchtop power supply with no (very small) load, I am seeing ~100mA @ 43V. Is it normal for this converter design to dissipate 4W with little to no load?

3 months ago

0 Timothy Hegarty 3 months ago

TI__Guru 55472 points

Hi Nicolas,

I suspect you have huge inductor core loss and/or FET switching loss.

Send on a completed quickstart calculator file so we can examine the power losses: https://www.ti.com/tool/LM5146DESIGN-CALC

PS: given the max Vin of 58V, the LM5145 75V version is sufficient here. Note we have a 24V output application circuit example in the LM5145 datasheet.

Regards,

Tim

0 NIcolas Gallardo 3 months ago in reply to Timothy Hegarty

Prodigy 40 points

Hi Tim,

I've completed the quick start calculator and attached it, along with the inductor core loss specs, and the original Workbench circuit output I based this design off of. I believe you are correct about large inductor core core losses. Is there a way to reduce this loss, should I just search around for a similarly spec'd inductor with less loss characteristics?

Thanks for your help,

Nico

WBDesign1 (2).pdf

LM5146-Q1 Quickstart Tool r2 - 48Vin 24Vout 8A 255kHz.xlsm

0 Timothy Hegarty 3 months ago in reply to NIcolas Gallardo

TI__Guru 55472 points

Try Cyntec VCHA105D series inductors for much lower core loss.

https://www.cyntec.com/CoreLossCalculator.aspx?id=7

0 Timothy Hegarty 3 months ago in reply to Timothy Hegarty

TI__Guru 55472 points

The quickstart looks looks okay. You may want to use 80V FETs for better efficiency (see the family of FETs on the LM5145 EVM as an example). And go with asymmetric FETs, i.e. higher Rdson for the high side. The Qrr of 275nC is huge, so you may want to use higher Rdson for the low side as well. I went with CSD19534Q5A in apps example #3 in the LM5145 datasheet.

Also, you could crossover at a higher frequency, e.g. 30kHz.

If you can't find an inductor with lower core loss, go ahead and increase the inductance to 22uH (lower ripple current = lower core loss).

Tim

Power management

Power management forum

LM5146: No load current