I have designed a PCB based on Arduino MEGA 2560 and RAMPS, with some differents:
- It works at 24V with drivers drv2580
- The communication is based on FTDI driver and an USB connection.
- There is a comparator which selects the 5V from USB or power supply, based on a PNP transistor. The 5V is obtained from 24 V using this DC-DC converter: OKI-78SR-5/1.5-W36H-C.
- The 5V pin from USB has a fuse of 500mA, whereas the two pins of 24V have a fuse of 5A.
- The case of the USB connector is connected to ground through a ferrite core.
- There is an unique GND plane both USB and power source.
Recently I had a problem in my machine where the USB heats up and is burnt and the computer crashes, when it has been connected to the PCB and the 24V power supply turns on.
After this problem, I made the next analysis:
The origin of the USB cable heat is due to the GND pin is absorbing too much current for some reason and this also causes that the computer crashes.
The origin of this high current can be a short circuit, and the current comes from power source, not from USB connection, because it has a 500mA fuse and this component is still working perfectly. The 5A fuses are also working, therefore, this short drifts the current through the USB GND and not to power source GND.
When I connect the PCB with the computer, the connection works correctly. Also when PCB with the power source. This suggests that the problem could be the 5V source selector, but as it is working correctly for both cases, I do not believe this is my problem. The source selector is similar to Arduino MEGA 2560 has integrated.
I have reviewed the machine design, but at first it not seems something is causing this problem.
I keep waiting some help of you, I really appreciate it.
Thank you very much. Best regards, Antonio.