I have a requirement for a XIAO nRF52840 running on battery to use as a BLE sensor node. It is reading multiple DS18B20 temp sensors using OneWire.
It works well with a 18650 battery connected to the battery pins, with a sleep current of 5.6uA.
I would like to use a physically smaller battery but the DS18B20 Vmin is 3.2v so I can’t use a single CR2032 coin battery, I did think of using two in series but as this would produce between 4-6v I would need to connect to the VIN pin.
My testing has shown that when supplying 5V, via my Power Profiler Kit 2, to the VIN pin I am seeing a sleep current of 5.4mA, this appears to be way off what I was expecting.
Looking at the SGM2040 voltage reg data sheet it shows a Load Regulation of 3 to 15mA. Does this mean that using the VIN pin the best case sleep current will be in the 3-5mA range?
The power supply circuit of the XIAO nRF52840 is probably as shown in the link below, and looking at the PPK2 current waveform, I suspect that the battery charge controller is consuming a large amount of current to detect whether the battery is connected.
(The load regulation of the voltage regulator is 3-15 mV)
Can you use a 3.7V rechargeable button-type lithium battery?
‘Charging characteristics of XIAO_nRF52840 and XIAO_ESP32C3 - #2 by msfujino’
The module is not designed to work with CR2032 (or other battery). It is better to use small battery, let said 150mAH, which is almost the same size as the CR2032 (and smaller that CR2x2032)
Forcing voltage on VIN as high than 6V (2 times CR2032) will probabely be kiling for some part when you are going to connect the USB (for downloading your FW for example).
Ah yes, I misread the Power regulation as mA not mV, good catch.
I had looked at that post but was focused on the power regulator, but it sounds possible that the charge controller is burning current even without the battery being connected.
I will look for a 3.7v that fits the form factor.