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LMX2594: OSC Off --> ON Test

user5163865
Genius 3970 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMK04828, TIDA-01022

Hi,

Our customer performed a test that intentionally shuts down the REF OSC, taking into account any errors, and complained that the OSC oscillation could be restarted and still be out of control.
1) Is there a way to return to normal operation by OSC Off-> ON?
2) The VCO shuts down when control is lost. Is this correct? Other PLLs return without any problems in the same test, and the VCO does not stop even when OSC is off (VCO is fixed at the upper limit frequency).

In customer testing, the LMX2594 did not restart without a RESET.
Best regards,
Hiroshi
  • 0
    TI__Guru** 106720 points

    Hi Hiroshi-san,

    If the ref clock stop working, LMX2594 will unlock, VCO frequency will be off but there will be signal output. When the ref clock is resumed, I believe it will track and lock again. If it does not lock, programming R0 once again shall bring it to the lock state. I've never seen out of control after losing the ref clock.

  • 0 in reply to Noel Fung
    Genius 3970 points

    Hi Noel-san,

    Thank you for your support.

    If it works properly, is ref clock off-> on and no special operation required?
    What if I need to write R0?
    For example, if the lock time is long due to the loop filter setting?

    Customers evaluate this system because the REF clock is supplied externally via the LMK04828.

    The output of the PLL is supplied to ADC12DJxx00.

    This system is similar to TIDA-01022.
    Best regards,
    Hiroshi




  • 0 in reply to user5163865
    TI__Guru** 106720 points

    Hi Hiroshi-san,

    Right, there should be no operation needed when the reference clock has came back, LMX should be able to track and lock again.

    Programming R0 will initiate a VCO calibration. The loop will be first get opened; VCO gets calibrated; and then loop closed again in order to lock to the reference clock. In other words, program R0 once will break (or reset) the close-loop.

  • 0 in reply to Noel Fung
    Genius 3970 points

    Thank you for your reply.

    I believe SPI control is incorrect because they say LMX2594 are out of control.

    So I'll mark this thread as resolved.

    Best regards,

    Hiroshi