TS3A5018: TS3A5018 unused pins

Hi Andy,

The short answer is its not recommended and it is best practice to terminate unused analog I/O pins on these types of multiplexers with a 50 Ohm resistor to ground.

Long answer you can but there are consequences for doing so, however they may not provide much impact. Essentially if a system undergoes transmission line effects (which as a general rule of thumb this is to take path length, L,   from source to load and compare it to the wavelength of the signal which can generally be approximated as λ = c / f (speed of light divided by signal frequency) and if  λ/16 < L than transmission line effects are going to occur) then there is the possibility of reflections due to the unterminated floating analog I/O pins as there are parasitic connections between I/O pathways. When these are terminated it helps mitigate issues due to reflections. However if the path length of the circuit is less than 1/16 of the wavelength you can ignore any transmission line effects and leaving pins floating is okay. If the path length is between 1/16 and 1/10 of the wavelength the transmission line effects may be negligible enough where floating will not cause a large issue either. So it depends on the exact application setup including physical geometry on which way you want to proceed. 

If you have any other questions please let me know!

Best,

Parker Dodson