nRF52840: What is the input impedance of the ADC inputs ? In spec it is greater than 1M but how much.
We would be happy with 5M ohms mean value.
nRF52840: What is the input impedance of the ADC inputs ? In spec it is greater than 1M but how much.
We would be happy with 5M ohms mean value.
Hi Thierry,
The input impedance, when SAADC is IDLE, is much greater than 5 Mohm.
When a ADC conversion is on-going, you switch in a capacitor as well as the input impedance and pin-capacitance, which will lower the impedance (see figure 8 here for more details).
Kind regards,
Håkon
As Håkon stated, it is just switched capacitance input. As are most ADC's.
You just use the e^(t/RC) relationship to figure out the sample time vs. input impedance appropriate for your design. R is of course the source thevenin equivalent from whatever your source is.
Unfortunately, for my application, this is not enough information. Our source impedance is 600k, so 5M input impedance would be too low. Can you please provide a better figure for the input impedance. It needs to be much bigger than 5M; hopefully it is.
See this post, this applies for the nRF52 as well.
Thank you for the white paper on battery measurement. It is exactly what we want to do.