JAJSCX6B January 2017 – July 2019 LMK04610
PRODUCTION DATA.
The digital lock detect circuit is used to determine PLL1 locked and PLL2 locked. A window size and lock count register are programmed to set a ppm frequency accuracy of reference to feedback signals of the PLL for each event to occur. When a PLL digital lock event occurs the PLL's digital lock detect is asserted true.
EVENT | PLL | WINDOW SIZE | LOCK COUNT |
---|---|---|---|
PLL1 Lock | PLL1 | PLL1_LD_WNDW_SIZE | PLL1_LOCKDET_CYC_CNT * (1 + (31 * PLL1_LCKDET_BY_32)) |
PLL2 Lock (Initial) | PLL2 | PLL2_LD_WNDW_SIZE_INITIAL = 1 ns | PLL2_LOCKDET_CYC_CNT_INITIAL |
PLL2 Lock | PLL2 | PLL2_LD_WNDW_SIZE = 1 ns | PLL2_LOCKDET_CYC_CNT |
For a digital lock detect event to occur there must be a lock count number of a count frequency during which the time/phase error of the PLLX_R reference and PLLX_N feedback signal edges are within the user programmable window size. Because there must be at least lock count number of count frequency cycles, a minimum digital lock detect assert time can be calculated as lock count / count frequency where count frequency = PLL2 phase detector frequency. PLL2 lock time is the sum of the PLL2 Lock (Initial) + PLL2 Lock time.
By using Equation 1, values for a lock count and window size can be chosen to set the frequency accuracy required by the system in ppm before the digital lock detect event occurs:
The effect of the lock count value is that it shortens the effective lock window size by dividing the window size by lock count.
If at any time the PLLX_R reference and PLLX_N feedback signals are outside the time window set by window size, then the lock count value is reset to 0.