Battery level less than 3.6V: is a resistor necessary?

[Daniel Reisfeld]

Hi,

I would like to check battery level using the SAADC of the nrf52840.

Assuming the voltage is less than 3.6V, do I need to have a resistor between the battery and the analog pin? If not, should the acquisition time be 3 micro-seconds?

Thanks,

Daniel

[Nguyen Hoan Hoang]

If your nrf is directly powered by the battery, you don't even need to connect to the analog pin.  Do the acquisition from internal VDD.  If nrf is powered by a regulator then you need to add a resistor divider to match the voltage of your VDD.

[Daniel Reisfeld]

Thanks!

I guess the answer for my second question is indeed 3 micro-seconds - right?

Daniel

[Nguyen Hoan Hoang]

It is not related to whether you have a resistor or not.

[Daniel Reisfeld]

If there is no resistor?

[Einar Thorsrud]

You can see from the SAADC electrical specification that a acquisition time of 3 µs is sufficient as long as the source resistance is <= 10 kΩ. And that is certainly the case when you measure directly without any resistor.