What do you think about this USB‑C as a debug port during development and as a charging port in production?
I’m designing a board where the USB‑C port will act as a normal charging port in production, but during development I want to use the same connector as a UART debug interface together with a standard FTDI breakout board.
TX/RX are routed to SBU1/SBU2, and DTR is routed to D+ through jumpers (only populated during development).
For the auto‑reset pulse, I’m using this circuit:
- DTR/D+ → 4.7 µF series capacitor
- → 330 Ω series resistor
- → RESET pin
- RESET has a 10 kΩ pull‑up to VCC
Goals:
- DTR should generate a clean reset pulse when opening the serial port.
- In production the jumpers are removed, so D+ and the SBU lines are unused and the port behaves as a normal USB‑C charging sink.
- If someone accidentally plugs in a real USB‑C cable during development, the MCU should not be damaged (USB2 activity on D+ should be heavily attenuated by the series C+R).
What do you think about this idea?
Does this look electrically safe and reasonable? Any concerns about the RC values or the topology?
Posted Mar 5, 2026, 7:49 PM UTC
21