NRF51 ADC max input resistance

[e.plotkin]

Hello, I red a Reference manual v3.0 for NRF51, chapter 31.1.3 (Input impedance). And I did not understand information about impedance. What maximal input resistance can be for correct ADC measurement data?

[Vidar Berg]

The RM states that the series resistance from the measured source should be less than 1 kΩ. This is because the ADC will draw some current while sampling and therefore causing a significant drop on the measured voltage if the series resistance is too high.

One alternative, if the resistance in your case exceeds 1kΩ, is to add a charging capacitor to the circuit. More details on this approach can be found in this blog post.

[Hardik]

Values used is in Megaohm to reduce current drain during Sampling.

Simply adding capacitor will help in matching source impedance less than 1K.

Is it true for all scenario for monitoring battery voltage???

Please clear these doubt.