I need to increase the CM5 5V rail, not decrease it. If you increase the CM5 5v rail to 5.3V, it will boot everytime, but that is just a bandaide over a bigger problem. One that I was using before I found the actual problem. But now I'm running the ragged edge of the HDMI spec at 5.3V and it's now touching everything else in my design.You could a load resistor on the 5v rail on the CM IO board to see if you can blead off the excess power.
Solutions I've considered:
5.1V 1% precision clamping zener, but with 300pF, it's going blow the HDMI 50pf source limit. I can require my device to use only short cables in application, but that is less ideal.
There are a couple HDMI port protection devices that have backdrive protection, ex. TPD12S521. But they are old and a lot of them are going obsolete. More importantly trying to solve this in the late stages of my design means redoing all of my hdmi. I not particularly thrilled with that idea.
Statistics: Posted by sel_lab — Tue Feb 03, 2026 11:13 pm