ARM JTAG USB-TINY-H - device not recognized after some replugs

[kubeqz]

Hi, in the company where I work we ordered few of USB-TINY-H JTAG adapters. Already we have at least two showing the same problem with 'device not recognized' in device manager (code 43, VID=0, PID=2). It looks like the FTDI chip is broken, it cannot enumerate properly on the USB.

I wonder if that might be caused by the fact that we are connecting PCs with other HW (like dev boards, etc.) and each side is powered from separate power supply. Connecting with JTAG results in connecting grounds and some charge might flow until grounds are at the same level. That in result might induce some voltage on USB data lines going to the FTDI and destroy it (in fact, I saw there are no TVS diode on the data line in the USB-TINY-H).

Did you observe similar issues ? Any advice how to avoid it ?

[LubOlimex]

Yes, entirely possible to have voltage difference if you have more than one GND.

You may first want to measure it - just disconnect everything and measure the voltage between the GNDs of PC's USB and the GND of the adapter or variable power supply in question. I've seen voltage difference of 100V and more in that scenario which is dangerous.

Since we have this same scenario often while testing each board here (where a target board has multiple power supplies applied simultaneously) - we have connected the GNDs of computers and voltage adapters beforehand. So that is the best solution I can recommend - tie all power supplies GNDs before connecting the supplies and the JTAG to the target!

Another worth-a-try solution is using USB insulator like USB-ISO without external power supply: https://www.olimex.com/Products/USB-Modules/USB-ISO/ - while it won't eliminate the problem completely it should make it harder to manifest and will protect your PC.