I'm trying to design a circuit with an ESP32-Mini that connects to a CAN bus via an SN65HVD230. I've added an MCP2221A as a USB/UART interface to the ESP32 so that I can program the chip while on board. The whole board is mean to attach to a BMW stick shift that requires a 12v supply.

I've breadboarded the circuit with all the different components on breakout boards, and the breadboarded version seems to work fine. However the whole circuit together doesn't seem to work and I can't find the problem.

The MCP2221A is responsive. I'm able to send it commands via USB and see responses. I don't see any information on the UART lines for the ESP32. Additionally, if I add 12v the board seems to get warm (which doesn't seem good).

I've got 5v from USB. The MCP2221A wants 5v. I've got an MCP1700 linear regulator for 5v->3.3v. The ESP32 and the SN65HVD230 want 3.3v. I've also got an MPM3610 buck converter to step the 12v down to 3.3v.

Clearly there is a problem with the circuit I designed, but I can't see the problem. Can someone please help?

Here is the schematic I designed:


Here is the PCB design:


Any help would be greatly appreciated, and if there is more information I can post to help debug the issue please let me know.


  • \$\begingroup\$ note - the esp32 module requires the 3V3 supply 22uF capacitor close to the module and the 3V3 track needs to be thicker. Pay close attention to your power distribution. \$\endgroup\$
    – Kartman
    Oct 1, 2022 at 23:41

1 Answer 1


That schematic makes the MCP2221A IO pins to use 5V logic levels. The ESP32 does not work with 5V levels but 3.3V levels. The ESP32 pins may be damaged with overvoltage. You likely want to use the MCP with 3.3V IO voltage, see datasheet for schematics. The VUSB pin capacitor is anyway about 10 times too small.

Also both regulators drive the 3.3V supply. Make sure the unused regulator can handle 3.3V being driven there.

  • \$\begingroup\$ Argh, you are totally right. I'm not sure how I missed the 5v levels on the MCP2221a. Thank you so much! \$\endgroup\$
    – Aaron
    Oct 1, 2022 at 20:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.