Measuring Vbat (2xAAA cell) with nRF52

[yulya]

Hello, I tryed to find in Q&A something that can help me understand how it is possible to measure battery voltage with nRF52, but i am not sure i found the exact explanations. I am using primary 2xAAA cell (meaning 3v when fresh and it is going low until ~ 1.6v , although we will probably stop system operation below 2v). I would like to perform as accurate measurements as possible with A/D of nRF52. Do i need to add additional hardware? Basically, usually A/D demands low impedance input to operate properly and some capacitor is recommended at its input. If i had higher voltage, i would probably add some resistor devider network with some N-MOS in order to save energy and have the lowest current consumption possible, but what about the case where the power voltage is the same as Vcc of the chip?

thank you for your help. BR, Yulya

[AmbystomaLabs]

Well, not really sure where you are looking and not finding the info.
This search alone brought up 226 answered questions on measuring battery voltage. devzone.nordicsemi.com/.../

But to answer it again, no you do not need additional hardware to measure Vdd. The SAADC can be configured through its registers to measure Vdd internally. See the nRF product spec in the SAADC section on how to configure this. The SAADC uses system voltage 1.3V as Vref. It has an internal prescaler to put voltages above Vref within its fullscale range.

With regard to operating at 1.6V, this is prohibited by the nRF. Vdd below 1.7V triggers a brownout reset. Refer to the power supply section of the nRF product spec for info on brownout behavior.