4.3.2 PLL Operational Modes

PLL operational modes depend on how feedback is received by the PLL. The VCO frequency varies based on the feedback mode that the PLL is currently in. The VCO operating frequency ranges from 800 MHz to 5000 MHz. The following are the three PLL operational feedback modes:

• Internal post-VCO
• Internal post-divider
• External

The frequency presented to the output dividers (OUTDIVx) is VCO/4. The CCC configurator configures all the internal dividers (RFDIV, FBDIV, and OUTDIVx) with appropriate values based on the reference clock frequency and the requested PLL output frequency. If the requested PLL output frequency is not achievable, the CCC configurator calculates the two nearest (lower and higher) possible output frequencies to select from, and sets the dividers accordingly.

The total feedback divide value (FBDIV) is equal to:

• FBDIV, when PLL is configured for Integer mode
• FBDIV + FRAC/2^24, when PLL is configured for Fractional mode