Hi Nordic HW support team,
In our product we have an analog input that can vary in a large range, e.g. from 0V to 1.2V.
In order to have a good resolution in the SAADC measurement while the input is at the lower end, vs. on the higher end, we'd like to implement a "dynamic gain" feature (in firmware), to change the gain accordingly to get the best resolution. We're using internal reference on nRF52840, i.e. 0.6V.
i.e.
if SAADC measured counts exceeded max -> reduce gain and sample until we have a measurement that's not exceeding max counts. (proper gain was found)
if SAADC measured counts that's a small fraction of max -> increase gain and sample until we have a good resolution.
Since the signal is changing randomly we don't know how large input*gain would be, but we know input is below VDD of course.
My question is if input*gain exceeds the reference voltage (i.e. internal ref in our case) VDD does that damage the processor?
e.g. if gain is set to 2x. and AIN is connected to 1.2v, that's 2.4V and above the 0.6v ref. is that damaging anything?
copied this from datasheet where "input range" is calculated
if we go by this calc then with a gain of 2x, input range is limited to 0.6/2 = 300mv? is this just to get a count below full scale or is there a hardware part that could get damaged if input was above 0.3V?
