Thank you, Kai!
Your comment is very clear and helpfull.
I am using a Vref=2.048V, so LSB is 2mV. Given the maximum input current of 1uA, I was thinking of using a 470ohm resistance (voltage drop accross it would be at max 0.47mV, which is less then 1/4 of LSB), and a polarized (electrolytic) capacitor of 1uF. Is the electrolytic capacitor poor in performance? Should I try to use a smaller nonpolarized capacitor?

Thank you!