Basic problem description:
For a given voltage input the ADC code generated is greater than expected.
Detailed problem Description:
10uA Burn-out current was selected on AIN3 and AIN4 pins via the System Control register. These pins were connected to a 1500ohm resistor. As expected 15mV was developed across the resistor and between pins AIN3 and AIN4. However, the resultant ADC code was greater than what 15mv should give. After some investigation it appears as if there is roughly an additional fixed 850ohm within the ADC that the burn-out current also develops a voltage across resulting in a larger ADC code than expected. If I take this suspected internal 850ohm resistance into account, then my ADC codes are correct for whatever external resistance I use.
Does this ADC have internal resistance that the burn-out current develops a voltage across or is there some other reason for the larger ADC code?
If there is internal resistance, then what is the range of this resistance?