LPC824, loading effect of ADC really that high?

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Apr 7, 2017 by vojtechhavlicek
Content originally posted in LPCWare by rayhofmann on Wed Jun 03 05:19:48 MST 2015
I am not sure if there is something wrong in my circuit or the software because the loading of the ADC looks a bit strong.

The loading effect varies with what other channels it is sampling, it may be coming from low or high voltages. The example is with no other channel active. It does two identical conversions in sequence on one channel only, both loading effects look the same.

The source impedance is about 2KR, the added probe capacitance maybe 10pF plus 5pF stray on the board.

Or did i damage my part? There definitely was one incident where i shorted some power supply with the probe, but not directly the 3.3V supply of the LPC, so it was a bit isolated behind a regulator that obviously survived.

Maybe i just need a really low source impedance lower than 500R?