LMX2594: LMX2594 Frequency drift spec when Lock Detect is high?

Derek,

The MUXout pin for measuring calibration time is good for automatic modes, but I don't know if you can fully trust it for manual modes. We have seen calibration down more like 3 us, but this depends on write speed.

Let's first talk about lock detect in automatic VCO calibration mode ...
VCOCal lock detect is supposed to go high when VCO calibration is done, regardless if the PLL is locked or not. For instance, if you lock the LMX2594 and lock detect goes high, then you can change the input reference frequency or do something else to make it go out of lock and lock detect stays high. Only when you re-run the calibration does it let the lock detect go low

Now Vtune and VCOCal lock detect does look at the phase as a gross indicator and if you were consistently off by 100 Hz, it would tell you, but the frequency was transitioning, then it might not catch this.

In other words, lock detect is only intended as a gross indicator of lock.


Now in Full assist mode, I'm not sure what VCO calibration lock detect means. It is likely going high after you write some register. Vtune and VCOCal lock detect should go high when you are close in frequency but this includes some of the analog settling time of the PLL loop, which depends on external components.

Regards,
Dean