Why do my Trinket M0s die?

[0x3c33]

Dear nice electronics people,

I'm working on a Eurorack module based on a Trinket M0. Somehow I managed to kill three Trinkets already and I don't know how. Could you please take a look at my attached schematic? Maybe you can see what I'm doing wrong.

Screenshot 2023-03-19 at 16.25.32.png (78.52 KiB) Viewed 77 times

Normally the power supply of the module are the -12V, +12V rails of the Eurorack power bus. But when I plug in USB there is also +5V from USB. So there are three different possible constellations of power "supply".

• -12V, +12V from the Eurorack power bus (driving the Trinket MO from a LM78L05 voltage regulator)
• +5V from USB only (maybe not so healthy? I try to avoid this, but sometimes it happens)
• -12V, +12V from power bus and +5V from USB at the same time

Do you see my mistake? Are you having tips for me to get this thing a bit more robust?

Thanks a lot!

[CGrover]

"It's likely that the C_In/Out that uses D5 for overvoltage protection could place > +3v on the Trinket’s 3.3v pin, back-charging the on-board 3.3v regulator and overpowering the MCU. A series resistance of 1k to 4.7k ohms should be sufficient. Also, recommend increasing R12 and R17 similarly since the outputs of IC1B and IC1D could easily exceed +3.3v and create a similar issue. I'll post this observation to the forum, as well."

-> from my post in Adafruit Discord: help-with-hw-design https://discord.com/channels/3272547085 ... 5431368835

[0x3c33]

Thank you very much. I'll try that.