This photo shows the power conversion side of two versions of the same board. Input is up to 60V DC, board converts to 5V and then down to 3.3V.
The top board works correctly all the time. But the bottom board has strange issues. Everything works perfectly when I connect it to my bench power supply at 53V. The board powers up with no problems. When I connect it to the daisy chain of other boards, it suddenly will no longer power on, despite ~54V being passed through correctly to downstream boards.
This is a real head-scratcher for me, and I’m having trouble making sense of it. I’m not so much looking for The Solution as to what steps I should take to troubleshoot this. There were some issues attaching the image, so in case it doesn’t show up.
You can try checking whether the 54v supply has any voltage spikes if you haven’t already. 60-to-5 converter is most likely a switching converter and they draw high current instantaneously and can cause spikes if not filtered properly which may affect the functionality. This may not show up in DC voltage measurement, and daisy chained boards may still function if they are filtered well. One of the daisy-chained boards may be causing the disturbance too, and maybe top board is filtered well but bottom isn’t for some reason, maybe a soldering error(e.g. filter capscitor ground connection, poor soldering may be conductive but with high inductance, hindering filter functionality). So it is good to check supply quality. Also what do you mean by not powering up? Is 3.3v not working? What about 5v?
Correct, it’s a switching converter, the MAX17640. 5V is not powering up (getting ~2V out) and then the 3.3V LDO is not powering up.
I put an older variant daisy-chained board before and after the newer board. Both of the older ones come up, but the newer one doesn’t.
I will check soldering disturbances and put my scope on the input line to see if there’s a lot of noise. Thank you!