Hello Shay,
Welcome to the TI E2E community!
If you use bipolar supplies (AVSS=-2.5V and AVDD=+2.5V), then you can connect AINM to ground. In this case, you will be limited to a maximum input voltage of +/-1.25V on the gain=1 range. Since this is also the full scale input range when using gain=2, for best performance, you should use minimum gain=2.
If you want best possible performance from the ADC or you want to use a single +5V supply, then you can use a fully differential amplifier to convert your single-ended input to a fully differential output. The THP210 would be a good choice in this case. You can use the circuit in Figure 9-12 of the THP210 datasheet, and set Vocm=+2.5V when using a single 5V supply.
Regards,
Keith Nicholas
Precision ADC Applications
