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LMX2571 LOCK DETECTION TIME USING INTERNAL VCO

Jerry Wanger
Prodigy 10 points

Other Parts Discussed in Thread: LMX2571

Using a LMX2571 with the internal VCO, what is the typical lock detection time?

Does attaching an external filter to CPout pin (Pin 25) affect the results and by how much?

Is the internal loop filter usually good enough?

I am planning on using this part in a DMR radio and I am worried about the TX to RX timing when doing handshaking when connecting to a repeater.

Jerry Wanger

  • 0
    TI__Expert 4085 points
    Hi Jerry,

    Thank you for your interest in our products. We received your question and will be answering it as soon as possible. We appreciate your patience.

    Best regards,
    Julian
  • 0 in reply to Julian Di Matteo
    TI__Guru** 121130 points
    Hi Jerry,

    With internal VCO, the total PLL lock time = register programming time + VCO calibration time + analog loop lock time.
    Register programming time depends on the programming speed as well as how many registers are required to write.
    Typical VCO calibration time is about 140us.
    Analog loop lock time depends on the loop bandwidth. For a 200kHz loop bandwidth, lock time is approx. equal to 20us.

    Please note pin 25 requires connecting to the first and second pole of the loop filter, they are not integrated.
    The switching time between TX and RX is very fast, please read the example in section 8.2.1 in the datasheet.