Hello everyone,
I am planning to create a battery supply board that will connect to the Arduino Nano 33 BLE Sense Rev 2 using header connectors as seen in the image below. The device is intended to be very compact to be used as a wearable.
This battery supply board will have a battery charging circuit and a coin cell holder attached to it.
I am currently looking at the TP4056 Li-Ion battery charging module to be responsible for preventing over charging and over discharging. My plan is to battery power the board through the “Vin” pin of the Arduino, as recommended by the Arduino website.
The issue I am running into is that the Arduino documentation states that the Vin input voltage must be greater than 5V, and lithium-ion cells only provide 3.7V each. I thought about using a boost converter to boost the voltage to 5V, or attaching to cells in series. Although when looking more into the voltage limits of Vin, I didn't fully understand why the voltage limit was a minimum of 5V.
The datasheet for the Arduino says that Vin needs to be greater than 5V due to the regulator specifications of the voltage input.
Arduino data sheet: https://content.arduino.cc/assets/NANO33BLE_V2.0_sch.pdf
Although, I looked up the voltage regulator (MP2322GQH) datasheet and it seems that it can handle an input voltage of 3V – 22V.
https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP2322/
I thought maybe the issue may be with the diode in the Arduino regulator circuit shown below allowing both Vusb and Vin to feed into the same node if the USB was plugged in AND Vin was less than 5V. Although I am not sure….
I have come up with a possible “load-sharing” circuit to switch the regulator input of the Arduino to the USB power when the Arduino is plugged into the USB and cut-off the Vin battery power supply. So, when both the USB is plugged in and the battery is connected to Vin, the board will use the USB voltage to power the board while also allowing the battery to be charged by the USB voltage. When the USB is disconnected, the board will switch to the Vin battery voltage input. We would use a P-Channel MOSFET and added resistor to implement this. Our plan was to implement the TP4056 module circuit and P-channel MOSFET circuit on one external board that will connect to the lithium-ion battery as well as the Arduino board as seen below:
This design is based off some Arduino forums we found linked below:
As well as the schematic of another microcontroller evaluation board called “ESP8266 FEATHER HUZZAH” that has integrated battery charging shown below:
My main goal is to maintain a small form factor by removing the requirement of a boost converter and being able to share 1 USB port to both charge the battery and upload sketches to the board.
Would this design approach work to switch regulator input from Vin to Vusb once the USB is plugged in while also charging the battery? I would love any feedback or suggestions!
Thanks!