SNAS816C March 2022 – February 2025 LMK5B33216
PRODUCTION DATA
Figure 8-2 shows the PLL architecture implemented in the LMK5B33216. The ultra-low jitter channel consists of a digital PLL (DPLL3) and the BAW APLL (APLL3) with integrated VCBO (VCO3). APLL2 with integrated LC VCO (VCO2) can generate a second low jitter clock frequency domain. The APLL2 feedback N divider numerator can be controlled by DPLL2. APLL1 with integrated LC VCO (VCO1) can be used as a third clock generation domain. APLL1's feedback N divider numerator can be controlled by DPLL1.
The DPLL is comprised of a time-to-digital converter (TDC), digital loop filter (DLF), and programmable 40-bit fractional feedback (FB) divider with sigma-delta-modulator (SDM). The APLLs are comprised of a reference (R) divider, phase-frequency detector (PFD), loop filter (LF), fractional feedback (N) divider with SDM, and VCO.
Each DPLL has a reference selection mux that allows the DPLL to be either locked to another VCO domain (Cascaded DPLL Operation) of the APLL or locked to any reference input (Independent DPLL Operation) to provide unique flexibility in frequency and phase control across multiple clock domains. The cascading architecture provides unique flexibility for hybrid synchronization of frequency and phase control across multiple clock domains.
Each APLL has a reference selection mux that allows the APLL to be either locked to the XO input or to the cascaded divider output of another APLL (APLL Cascaded With DPLL).
Do not cascade one VCO output to both the DPLL reference and APLL reference of the same DPLL+APLL pair.
Each APLL has a fixed 40-bit denominator controllable by the DPLL when locked to an input reference. When one or more of the APLL are operating without DPLL control in APLL only mode, a programmable 24-bit denominator is also available for selection to synthesize exact frequency ratios. TI recommends the programmable 24-bit denominator when implementing hybrid synchronization or cascading between frequency domains to maintain 0ppm frequency error without DPLL control.
Any unused DPLL or APLL must be disabled (powered-down) to save power. Each VCO of the APLL drives the clock distribution blocks using the respective VCO post-dividers. If the post-divider setting is 1 for the VCBO, then the post-divider is bypassed and the VCBO feeds the output clock distribution blocks directly.
The following sections describe the basic principles of DPLL and APLL operation. See DPLL Operating States for more details on the PLL modes of operation including holdover.