LTC2449 can't read low voltages (1mV)


I want to read ADC at high speed (Conversion Time=1.1ms) using DC742B Board and Linduino One Board. I connected the DC742B Board and the Linduino One Board with a ribbon cable. I have uploaded the DC590B code to Linduino One Board on github. Then I can apply voltage to any channel with the QuikEval K114 interface and read it through the interface. Also, when I select low value=206mV, high value=2.495V and calibrate two points, I can read 10mV and above with 1mV precision. When I apply a value below 10mV I see a constant value of around 9mV on the QuikEval Interface display. Also, when I do two point calibration with low value=0V, high value=2.495V values, the result does not change. When I try with different conversion time values, the result does not change.

I want to read correctly when I apply a value as low as 1mV and anything above it to the input of the ADC. What should I do for it?

Thank you.