I was having this issue with a RPi 5 powered via the 40-pin header from a custom carrier board. The 5V supply is generated using the CM4IO 12V to 5V circuit with the inductor changed to support the full 5A output the AP64501 is capable of. The system would randomly throw "hwmon hwmon3: Undervoltage detected!" dmesg warnings and running "stress -c 4" would cause a system shutdown within seconds (power LED turns red with no dmesg or console warnings about shutting down).Hello, our Raspberry Pi 5 has been experiencing undervoltage `dmesg` warnings and system shutdowns under certain loads. We've tried to diagnose this problem with an external power supply and found some surprising results.
The 5V regulator was about 150mm away from the RPi header, connected via a 1mm wide PCB trace which did not provide enough current carrying capability. The 5V rail at the regulator was fine, but on the 40-pin header I was seeing 100 mV drops when running "stress -c 4". Adding an 18ga wire from the 5V supply directly to pins 2 & 4 on the 40-pin socket for the RPi 5 seems to fix things. I've been running "stress -c 4" for several days now without a dmesg undervoltage warning or having the system shutdown.
The next PCB revision will move the 5V regulator to be much closer to the RPi header and use a copper pour instead of a trace for the 5V rail.
Statistics: Posted by cdsteinkuehler — Mon Jul 08, 2024 12:17 pm