SI5345 Datasheet, PDF (36/62 Pages) Silicon Laboratories – 10-CHANNEL, ANY-FREQUENCY, ANY-OUTPUT JITTER ATTENUATOR/CLOCK MULTIPLIER

Si5345/44/42
Figure 19. Example of Precise OOF Monitor Assertion and De-assertion Triggers
5.7.3.2. Fast OOF Monitor
Because the precision OOF monitor needs to provide 1 ppm of frequency measurement accuracy, it must measure
the monitored input clock frequencies over a relatively long period of time. This may be too slow to detect an input
clock that is quickly ramping in frequency. An additional level of OOF monitoring called the Fast OOF monitor runs
in parallel with the precision OOF monitors to quickly detect a ramping input frequency. The Fast OOF monitor
asserts OOF on an input clock frequency that has changed by greater than ±4000 ppm.
5.7.4. LOL Detection
The Loss Of Lock (LOL) monitor asserts a LOL register bit when the DSPLL has lost synchronization with its
selected input clock.
There is also a dedicated loss of lock pin that reflects the loss of lock condition. The LOL monitor functions by
measuring the frequency difference between the input and feedback clocks at the phase detector. There are two
LOL frequency monitors, one that sets the LOL indicator (LOL Set) and another that clears the indicator (LOL
Clear). An optional timer is available to delay clearing of the LOL indicator to allow additional time for the DSPLL to
completely lock to the input clock. The timer is also useful to prevent the LOL indicator from toggling or chattering
as the DSPLL completes lock acquisition. A block diagram of the LOL monitor is shown in Figure 20. The live LOL
register always displays the current LOL state and a sticky register always stays asserted until cleared. The LOL
pin reflects the current state of the LOL monitor.
Figure 20. LOL Status Indicators
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Rev. 1.0