Can I use a button in place of a clock crystal?
Page 4 of the datasheet you posted a link to. Note (3):


  Because the sample cap will eventually lose charge, effective clock rates below 10 kHz can affect linearity.


It then says "Refer to Section 6.2" which is on page 22.

From that section it says that the clock rate doesn't need to be constant for conversion, but at effective clock rates lower than 10kHz the charge on the sample capacitor leaks away and the result is inaccurate.

Basically this could work, but you won't get a sensible conversion result.



I'm tempted to just say, if it is just for debugging, "Try it and see". But don't do it for anything sensible.