Nano 33 BLE: Powering via Vin

[sebulba20]

I am planning to power the Arduino with a power supply via VIN because I have a lot of other peripherals that also need to be powered. The NANO33BLE_V2.0 schematic shows that to connect VIN to the board jumper SJ4 needs to be shorted, resulting in 3V3 being generated by MPM3610.

What I do not understand is how one can then safely connect a USB cable. When the USB cable is connected the NINA-B3X sub-circuit also generates 3V3 on the power bus. The two supply voltages will clash as they cannot be identical.

[Klaus_K]

If I am not mistaken SJ4 is the closed jumper at the bottom of the board labeled 3.3V. It allows you to disconnect the regulator from the device so you can power the board by a battery connected to 3.3V. You would need to remove the battery and connect the jumper when you want to reconnect USB again.

There is a diode between Vusb and Vin to stop a reverse voltage into Vusb from Vin. So, when Vin is larger than Vusb the board is powered by Vin and Vusb is disconnected.

[sebulba20]

Thanks for your reply. I am getting back to this project after a very long delay!


In my application VIN  = 5V. So I will need the regulator to generate 3.3V. The diode between VUSB and VIN is D2 and I see how it works provided that VIN > VUSB. But, ignoring the diode drop, when that is not the case then the VIN supply will be driven hard by VUSB.

I figure that to be safe I would have to disconnect D2. Alternatively, when a sketch is uploaded then VIN should be disconnected. Is there any other solution?

[Klaus_K]

I am not entirely sure what issue you are foreseeing.

You should be able to connect a USB cable even when you power the board trough Vin. D2 will stop a reverse voltage onto VUSB.

You should not power any large load from the Arduino. Any large load should be powered by a separate power supply. This is regardless of using Vin or VUSB. The MPM3610 should only be used for the Nano and a few sensors and other low power stuff. The converter has a large current rating, but the rest of the PCB and thermal design are not sufficient.

[sebulba20]

I attached a figure that might help.

The case you are thinking about is Case 1, which works fine. I am worried about Case 2, where the result is two power supplies being connected in parallel. VSUB will be trying to change VIN. I am not sure what will happen to the computer or the VIN PSU.

Thanks for the waning concerning the power capabilities of the PCB. I am using the 3.3V from the Arduino to drive low-power electronics. I need the 5V to drive a couple of sensors and wanted to use the same PSU to drive the Adruino.

[CrossRoads]

Use a diode from each Vsource to p16. Then neither one can backdrive the other.
My PC doesn't like when a board has the same or higher Vusb, it reports Surge Current and shuts down the port, requiring a PC restart to get it back.

[sebulba20]

Well of course! Why didn't I think of that? Thank you!