LM5148: LM5148RGYR output loss Vs high load

Hi Doron,

Please share the schematic of your design and share the filled in design calculator with me: https://www.ti.com/tool/LM5148-LM25148DESIGN-CALC

Thanks,

Best Regards,
Taru

Dear Taru,

Thanks for your reply and good will.

i used the webench tool, so i guess the best way is sending its report. 

+ i add the layout (Allegro) if needed. 

Thanks in advance

Doron

https://wetransfer.com/downloads/bb83f006f96802aaa13b46285c10ee5f20250317103207/2e17b78431d0ae4c1d8d70272b2ca23020250317103344/e03d00?t_exp=1742466727&t_lsid=dbed91aa-7b6f-4eaf-ad0a-c36ee91f2d56&t_network=email&t_rid=YXV0aDB8NjFhNzg1MDg0MDkzNTQwMDY4YzdhZGJj&t_s=download_link&t_ts=1742207624

Hi Doron,

The actual passives that you have used impact the loop stability of the design (DC Bias derating and ESR of the caps, etc.). Are the passives used in the WEBENCH design the SAME as the ones on your actual design? If not, I would request you to share the actual schematic and fill in the calculator accordingly.

Also, what is the input voltage supply to your board? Does it have enough current sourcing capabilities? 

Thanks,

Best Regards,

Taru

Dear Taru,

it seems i cant provide a good answer. The Chinese manufacturer probably used the caps he got in his stock.

i didnt specified a full part number for the caps, or limit its type (X5R/X7R/COG etc..), cause the pcb quantity was just samples for testing.

I only asked ceramic & low ESR caps.  i havnt realized how important it can be in such current... 

very good lesson... :-) 

WBDesign152.pdf - Google Drive

Can you please guide me on which cap(s) I should change in order to improve the situation.
Thanks again, and thanks in advance.

Doron

Hi Doron,

If you use the passives suggested by WEBENCH and the design was stable, I dont see a reason why the design wouldn't work. Inductor saturation is a probable cause here. The other reason could be the loop instability. Please check the current rating of the inductor being used here. 

Also, do you see any drops in the input power supply (insufficient power sourcing capability from the supply to the buck can be an issue)? 

Thanks,

Best Regards,

Taru