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LMH1983: question of PLL1

Part Number: LMH1983

Hello Experts,

If the external VCXO does not work (i.e. it is broken.), how does LMH1983 work? It will work on holdover or free-run mode? Also LMH1983 will indicate LOR?

Best Regards,
Fujiwara

  • Hello Fujiwara-san,

    Happy New Year, hope all is going well for you!

    The LMH1983 by default is programmed to work in holdover mode but can be reprogrammed to free-run mode. This associates with Register 0x05 bit 2 [LOR Mode].

    By default PLL1 is programmed to 27 MHz - same as reference signal - which means PLL could be providing this frequency but not 

    We can monitor Pin 11 'NO_LOCK' indicates loss of lock status flag for PLLs 1-4 (active high). On the Users Guide we can see that TP23 can be used as well as LED D3 to monitor LOR.