SNAS689A October 2017 – July 2019 LMK04228
PRODUCTION DATA.
To ensure proper JESD204B operation, the timing relationship between the SYSREF and the Device clock must be adjusted for optimum setup and hold time. The tsJESD204B defines the time between SYSREF and Device Clock for a specific condition of SYSREF divider and Device Clock digital delay. From this point, the SYSREF_DDLY. SDCLKoutY_DDLY, DCLKoutX_DDLY_CNTH, DCLKoutDDLY_CNTL, and DCLKoutX_MUX, SDCKLoutX_ADLY, and so forth, can be adjusted to provide the required setup and hold time between SYSREF and Device Clock.
It is possible to digitally adjust the SYSREF up to 20 VCO cycles before the SYSREF. So for example with a 2949.12-MHz VCO frequency, tsJESD204B + 20 × (1/VCO Frequency) = –80 ps + 20 × (1/2949.12 MHz) = 6.7 ns.