SBAS991 February 2021 ADC3663
The PDN/SYNC pin can be used to synchronize multiple devices using an external SYNC signal. The PDN/SYNC pin can be configured via SPI (SYNC EN bit) from power down to synchronization functionality and is latched in by the rising edge of the sampling clock as shown in Figure 8-35.
The synchronization signal is only required when using the decimation filter - either using the SPI SYNC register or the PDN/SYNC pin. It resets internal clock dividers used in the decimation filter and aligns the internal clocks as well as I and Q data within the same sample. If no SYNC signal is given the internal clock dividers will not be synchronized, which can lead to a fractional delay across different devices. The SYNC signal also resets the NCO phase and loads the new NCO frequency (same as the MIXER RESTART bit).
When trying to resynchronize during operation, the SYNC toggle should occur at 64*K clock cycles, where K is an integer. This ensures phase continuity of the clock divider.