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How to use fastlock and lock detect LMX23**

SF Cillari
Prodigy 10 points
Other Parts Discussed in Thread: LMX2541

I'm using a LMX23** pll to control a vco and want to use the fastlock option and the lock detection. Both options are using the same pin. So it's either fastlock or lock detect. 

When in lock I want to switch back the pin to LD and the Cp to 1ma and  feed back the status to the microcontroller.

 The problem is how do I detect when the loop is in lock when the pin is assigned to fastlock?

Simon

  • 0
    TI__Mastermind 28021 points

    Simon,


    The LMX23** series is a very old series of devices that does not have dedicated lock detect pins.  However, all our devices since this tend to have dedicated fastlock and lock detect pins.  So you might consider going to one of these devices, such as the LMX248X, LMX243X, or a device with an integrated VCO, such as the LMX2541.

    If you stick with the LMX23** series, then you do have a challenge.  You can change the charge pump current only, but you need to be careful with this because if it is not well-designed, then the loop filter can become unstable.   Another approach is to monitor the loop filter voltage.  The problem is that you also need to be very careful to this because loop fitlers are very sensitive to any kind of leakage currents.   So without switching to a newer device, there really isn't a very elegant solution for the LMX23** devices.

    Regards,

    Dean