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LMX2485

Sreelakshmi Radhakrishnan
Intellectual 315 points

Other Parts Discussed in Thread: LMX2485

Hi I am using  LMX2485 PLL with input freq 10 Mhz and VCO Frequency of 92.16 MHz.

Before the PLL is programmed when the supply is given the lock detect pin output is showing a pulse with a freq around 1KHz.It works fine when the chip is programmed with LD going high.Please help me with the issue.

 

  • 0
    TI__Mastermind 28031 points

    Sreelakshmi,

    If the LMX2485 is not programmed, you have to assume that the status of all the register bits is random;  there is no power on reset.   You might find that a particular chip on a particular day might exhibit some behavior, but you can not count on this to be consistent over devices, temperature, and voltage.

    The lock detect pin has many functions, including R divider output, N divider output, and so on.  So if you randomly get the R divider output then this could produce a signal.  Since you have not programmed the R divider, this R count could be anything.   It could also be the N divider output.

    In summary,  you can not predict the behavior of the device if it is not programmed.  Now once the device is programmed, or even if you program the N divider to a frequency that would cause the PLL to become unlocked, it should give a correct indication in this case.

    Regards,

    Dean