How to read in a 4.2V battery reading on a nRF51822

[tyler]

I am using a lithium polymer 4.2V battery to power an nRF51822 (as a side note the power goes through a voltage regulator before going to Vdd).  I want to be able to check if the battery is low by checking the voltage using an analog input pin on the nRF51822.  The problem I'm having is that the lowest prescaler value I see is for 1/3 which will still be too much voltage for the chip to handle.  Is there a way I can work around this in software?  If not am I going to have to implement something in hardware to make this reading?

[Martin Lesund]

Hi Tyler,

  Please take a look at the answer in this thread. I think that should answer your question. 

(updated links: Reference manual v3.0.1 Chapter 31  and Product specification v3.3, Chapter 7)

[Martin Lesund]

This Blog should also be helpful for you

[tyler]

Ok that blog is very useful.  I noticed that the maximum voltage the nRF51822 can read is 3.6V after a 1/3 prescaling with a reference to Vbg.  What I am wondering is if I put in a higher voltage (say 4V) will it actually damage the chip or will it just read the wrong voltage value?

[Martin Lesund]

I recommend you to stay in the recommended voltage range. 

If you go outside this specter it can result in unwanted behaviour. 

[tyler]

Ok that makes sense.  I happen to have a 3.3V voltage regulator on the board.  Could I use this as a reference for the battery instead of the 1.2V Vbg for the same 4.2V battery?