I have a project where I would like to power an Arduino Nano 33 BLE Sense with USB and Vin at the same time.

The idea is to charge an external LiPo 3.7V through a charger module that would take the load from the 3.3V pin (that would be powered through USB) and at the same time keep powering the Arduino through Vin because I want to avoid a power interruption when I unplugged the USB cable that would interrupt the writing operation (on a text file on an SD card).

So the goal is to prevent data corruption on a writing operation on a text file. I know text files are supposed to be less corruptible (compared to a database) but I want to be sure the operation would be uninterrupted.

I've seen this post: What happens if I power the Arduino with both the USB and external power voltage simultaneously? But it's related to the Arduino UNO R3.

It basically says: When Vin >6.6V the opamp turns the mosfet off.

so the USB disconnects.

When Vin <6.6V the opamp turns the mosfet on.

so the USB stays connected.

On Arduino's website: https://store-usa.arduino.cc/products/arduino-nano-33-ble-sense it says:

Vin: This pin can be used to power the board with a DC voltage source. If the power is fed through this pin, the USB power source is disconnected.

It does not mention from what voltage it would disconnect the USB power.

I did not find the same schematic for the Arduino Nano 33 BLE Sense. Just this:https://docs.arduino.cc/hardware/nano-33-ble-sense

Interactive Viewer Interact with the schematics, the PCB and a 3D model of the product.

and this: https://docs.arduino.cc/static/353d3c445c28b1da1fe1f9d6eafa948d/ABX00031-schematics.pdf

I'm not very familiar with reading schematics but I could not find similar information about vin and USBVCC.

That'd be great if somebody had some insight on that.

I would welcome any suggestion.


If I connect a battery charger/controller on VIN, my battery would be protected.

And I could connect a booster 5V and add a shottky diode so its connection to VIN would be closed if booster+ < VIN

Like this ?

charger + booster

1 Answer 1


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In this power block you can see there is only one Schottky diode with the voltage drop under 0.5V@2A. That means D2 is closed around the condition: VUSB < VIN.

On the other side if you add 3.6-4.2V battery on VIN there will be current flowing from VUSB to battery.

Basically you need another shottky diode Bat+ -> [A|K] -> VIN so when there is bigger voltage on the VIN it'll "shut off" the battery (otherwise it'll be charged by almost 5V)

Depending on the application and sensors you are planning to use, you might want to consider for example Seeed Studio XIAO nRF52840 Sense that has battery charging circuit and pads for the battery on the bottom (although it's not the "bread board" pins)

  • That's awesome! Thanks for the details. I thought I had to charge the battery through the 3.3V. But what you are showing is that VUSB feeds VIN. So if I connect a battery charger/controller on VIN, my battery would be protected. And I could connect a booster 5V and add a shottky diode so its connection to VIN would be closed if booster+ < VIN I even like the option with Seeed Studio XIAO nRF52840 Sense better. It's smaller than the Arduino 33 BLE Sense and it's got a USB-C connector.
    – Lguapo
    Apr 7 at 14:55
  • Do you even need booster? If you don't need 5V, you can use VIN for charging only and 3V3 output from accu. Definitely not step up connected to charging input
    – KIIV
    Apr 7 at 15:17
  • I need a booster because the minimum operating input voltage on VIN is 4.5V (on the Arduino 33 BLE). And I want to use a small 3.7v LiPo battery.
    – Lguapo
    Apr 7 at 15:49

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