Linux/ADS42LB69: Purpose of SYNC signal?

Hi Val
The primary use of the SYNC input is when the Input Clock Divider is being used, and the ADC needs to be synchronized to other converters or other activity in the system. The SYNC input would be used to set the input clock divider to a known phase with respect to the other system activity.
If the Input Clock Divider is not being used or synchronization to other activity is not needed, then the SYNC input is not required and the inputs can be terminated as described in the Pin Functions table.
I hope this is helpful.
Best regards,
Jim B