Problem with Boost Converter(LM5158 Q1) - Page 1
Forum section: electronics / projects

author: mechorican
author_rank: Newbie
timestamp: October 30, 2024, 09:37:49 pm
content: Hello everyone, I need your help. I designed a boost converter using TI's Webbench tool (LM5158 Q1), see photos. Unfortunately, the inductance gets very hot from around 70mA and higher. Does anyone have any advice as to where my design error lies? I want to convert 24V DC to 42V DC.

author: thm_w
author_rank: Super Contributor
timestamp: October 30, 2024, 09:54:14 pm
content: It would help to link the inductor:https://www.lcsc.com/product-detail/Power-Inductors_Sunltech-Tech-SLO1040H330MTT_C182163.html3.5A up to 3MHz, 80mR, it looks decent.Did you measure the operating frequency is as expected?Why is EP connected to nothing? From the datasheet: "Exposed pad of the package. The exposed pad must be connected to AGND and the large ground copper plane to decrease thermal resistance"

author: mechorican
author_rank: Newbie
timestamp: October 30, 2024, 10:04:31 pm
content: Quote from: thm_w on October 30, 2024, 09:54:14 pmOh, I didn't connect it because it isn't connected to the Webbench tool either. Could it explain the heating of the inductor?

author: thm_w
author_rank: Super Contributor
timestamp: October 30, 2024, 10:28:52 pm
content: Up to you to find out. Measure with oscilloscope as well.And layout is not ideal, I'm sure you'll get roasted for that. There should be a ground plane underneath this area instead of having a few ground tracks that don't connect directly and go off to nowhere.The next step after above would probably be to scratch up those ground traces on the bottom and connect them with jumper wire.

author: wraper
author_rank: Unknown
timestamp: October 30, 2024, 10:45:23 pm
content: This PCB layout is ridiculous for 2.2 MHz switching frequency. You're lucky it works at all.

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 31, 2024, 12:13:32 am
content: It could be improved massively for sure, but layout (or at least the general placement of things) itself isn't that bad imo. Other than the decidedly weak ground connection (that single poor via is taking the whole brunt of switching current!!!!) and maybe poor output caps selection.As we wait for your measurement, I have some observation rather unrelated to your problem: You don't need to go such length to match the exact component values. Especially not to the point of using 3 series resistor. Could've simply put 10k for RTand no one will ever notice the difference. Ditto 1k5 for RCOMP, and 82k : 2k0 for RFBdividers (heck, that one is actually exact, why are they recommending comparatively less common E96 values?)

author: wraper
author_rank: Unknown
timestamp: October 31, 2024, 12:21:26 am
content: Quote from: ArdWar on October 31, 2024, 12:13:32 amWeak GND is an understatement. Several GND traces are connected together somewhere outside of what's shown on the picture. And especially look on the path of output capacitors' GND. Feedback divider layout is absolutely ridiculous as well.

author: mechorican
author_rank: Newbie
timestamp: October 31, 2024, 08:41:08 am
content: Thank you for the feedback. I just do it as a hobby and have learned everything over the last 2 years. I will take your advice into account but go back to the LM5000 Boost Converter. That made it work. I tried to use the LM5158 because it was listed as more modern on the TI website. But it's a bit too complicated for my abilities. Thank you all.

author: tooki
author_rank: Super Contributor
timestamp: October 31, 2024, 10:46:04 am
content: Quote from: mechorican on October 31, 2024, 08:41:08 amLook at the example layout in the datasheet and above all the layout and schematic used in the evaluation kit. If you follow their example, you should do pretty well.Also take a look at this application note for the predecessor model. It explains the operating principles and how to lay out switching converters. The general principles apply to any DC-DC converter.