Sensitivity to power sequence

My Seeeduino XIAO is driving a stepper motor using TMC2209 in step-direction mode.
The power arrangements are:

  • External power supply of 12V feeds, through protection serial diode, the TMC2209 VM inputs and an on-board DC/DC converter that generates 5V.
  • The 5V feeds the Seeeduino, TMC2209 and some other components
  • The Seeduino generates 3.3V, that feeds some pull-up resistors with less than 10mA.
  • All the power sources are DC coupled and havew common ground.
  • The Seeeduino may also be connected to a PC through USB port for debugging.
  • Both the 5V and the 3.3V lines are filtered with electrolytic capacitors.
  • Edit: The strapping pins (D0, D8, D9) are connected to pull-up resistors.

I tested the various voltages:

  • With the 12V source on and USB connected
  • With the 12V source on and USB disconnected
  • With the 12V source off and USB connected
    I measured the voltages related to the external 12V return line and related to the Seeeduino GND pin. In all the cases all on-board voltages were within the tolerances (3.2V, 5.1V).

I downloaded the application - the motor cycled quitely to the correct direction, as expected. I noticed thet the 12V PSU may be on or off - the motor keep turning. I measured VM and found that when I switch the 12V off the VM drops to 4.9V. I am learning from this that the DC/DC feeds back the USB voltage. The protection diode protects the circuit from driving the external input line so I am OK with it.

  1. If I disconnect the USB the motor stops. The application will run again only if I close the IDE, disconnect the USB, shut down the 12V supply, then run the IDE, connect the USB, then compiles the sketch, upload it to the Seeduino and run it.
  2. Furthermore, it looks like the Seeeduino doesn’t keep the sketch.

Did anyone meet such phenomena? Since I experienced unsolved issues also with the ESP32 studio I reconsider using the Seeed products.


Sounds like the Seeeduino is not receiving power from the USB connection alone. The Seeeduino may require a separate power source (5V) to operate correctly, even when connected via USB.

Thank you for the reply. The Seeduino is fed from on-board DC/DC converted.I measured this with disconnected USB.