TMS320F280049C: DriverLib PLL Configuration Delay

In the DriverLib file, sysctl,.c, there is a delay added in the PLL configuration.  There is no reference to this delay in the TRM/Docs.

                    //

                    // Turn off PLL

                    //

                    EALLOW;

                    HWREGH(CLKCFG_BASE + SYSCTL_O_SYSPLLCTL1) &=

                        ~SYSCTL_SYSPLLCTL1_PLLEN;

                    SysCtl_delay(3U);

                    //

                    // Write multiplier, which automatically turns on the PLL

                    //

                    HWREGH(CLKCFG_BASE + SYSCTL_O_SYSPLLMULT) = pllMult;

Also, no code comment explaining.  Can you please provide details on this delay?

Thanks,

Eric