SAADC measuring below max when connected to VCC (when supplied by 3.0V)

[Maipei]

HI all,

I'm working on the nrf52840, and I've tested this on the devkit as well as on-board on the product I'm working on. Using the saadc, if I tie my AIN line to VCC, I consistently get readings of ~853 when the supply voltage is VCC=3..0V. The weird thing is that, if I use a 5V supply, I get VCC = 5V gives a saadc reading of 1023, as I would expect. I get a reading of 0 for ground in both cases, as I would expect. Any ideas on what might cause this? I thought that the adc readings were always relative to the input voltage, but it seems like these readings I get with the 3.0V supply are relative to 3.6V.

[Maipei]

I was being silly; I've figured it out. after reviewing the product spec, I see that the saadc example is likely using the internal 0.6V reference and a gain of 1/6, meaning that the highest measurement would be 3.6V.