ZHCSN15B June 2020 – June 2021 LMK05318B
PRODUCTION DATA
Zero-delay mode synchronization can be enabled to achieve deterministic (+/-1 VCO cycle) input-output phase delay between the selected DPLL reference input clock and the OUT7 clock as shown in Figure 9-31. This is primarily used to achieve deterministic phase relationship between a 1-PPS input and 1-PPS output. This feature can be configured through registers by enabling ZDM (DPLL_ZDM_SYNC_EN bit = 1) and enabling OUT7 divider synchronization (CH7_SYNC_EN bit = 1). The OUT7 clock must be derived from the DPLL and APLL1 VCO domain (fVCO1).
When the DPLL is not locked and the DPLL reference input is invalid, the OUT7 clock is held in mute state (no clock). Once the reference input is validated and selected, the OUT7 channel divider is reset or SYNCed using the DPLL reference input clock edge to achieve a deterministic phase relationship between the reference input and OUT7 clock. OUT7 is not affected by normal output SYNC events, and OUT[0:6] are not be affected by a ZDM SYNC event. The input-to-output phase offset can be adjusted through the DPLL phase offset register control (DPLL_REF_SYNC_PH_OFFSET bits). If the DPLL phase offset is programmed on-the-fly with 1-PPS input, it can take a long time to adjust due to the narrow DPLL bandwidth (10 mHz typical).
Hitless switching between 1-PPS inputs is not supported when ZDM is enabled. If a switchover event between 1-PPS inputs occurs when ZDM is enabled, a soft-reset should be issued for the DPLL to relock and realign the 1-PPS output to the selected input.