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LMX2572: at low temperature LMX2572 loss of lock in Full Assist mode

Amy Luo
Expert 6895 points
Part Number: LMX2572

Hi team,

The LMX2572 VCO calibrated 150 frequency points at room temperature. Reads back the values of VCO_SEL_force, VCO_CAPCTRL_force, VCO_DACISET_force and saves them in the flash of the MCU. At low temperatures of -40 degrees, power up the LMX2572, setting 150 frequency points in turn, and finding that about one third of the LMX2572 had some points unlocked. What could be the problem?

Best Regards,

Amy Luo

  • 0
    TI__Guru* 98180 points

    Hi Amy,

    Did you mean one third of LMX2572 devices or one third of frequency points (i.e. 50 frequency points) have locking issue?

  • 0 in reply to Noel Fung
    TI__Expert 6895 points

    Hi Noel,

    The customer feedback is below:

    There are 8 boards, each with two LMX2572. Two of these boards, both LMX2572 had some frequency points unlocked; Two of these boards, only one LMX2572 had some frequency points unlocked. Each LMX2572 has a different number of frequency points that are unlocked for cold start-up at -40°C. Two lmx2572 found only one point unlocked; three lmx2572 found less than 10 points unlocked; and one lmx2572 found more than 10 points unlocked. Also, I suspect that more unlocked points have not been found. At -40°C, 150 points have been tested, and the unlocked points are all within the first 50 points. I suspect that the heating of the device itself has properly locked the lmx2572 when the latter frequency points are tested. I also tested at -30°C and all lmx2572 were normal.

    Best Regards,

    Amy Luo

  • 0 in reply to Noel Fung
    TI__Expert 6895 points

    Hi Noel,

    The customer feedback is below:

    There are 8 boards, each with two LMX2572. Two of these boards, both LMX2572 had some frequency points unlocked; Two of these boards, only one LMX2572 had some frequency points unlocked. Each LMX2572 has a different number of frequency points that are unlocked for cold start-up at -40°C. Two lmx2572 found only one point unlocked; three lmx2572 found less than 10 points unlocked; and one lmx2572 found more than 10 points unlocked. Also, I suspect that more unlocked points have not been found. At -40°C, 150 points have been tested, and the unlocked points are all within the first 50 points. I suspect that the heating of the device itself has properly locked the lmx2572 when the latter frequency points are tested. I also tested at -30°C and all lmx2572 were normal.

    Best Regards,

    Amy Luo

  • 0 in reply to Noel Fung
    TI__Expert 6895 points

    Hi Noel,

    Do you have any updata?

    Thanks,

    Amy 

  • 0 in reply to Amy Luo
    TI__Guru* 98180 points

    Hi Amy,

    Your suspicion is reasonable.

    what are the decoupling capacitors at pin 3, 27 and 38?

  • 0 in reply to Noel Fung
    TI__Mastermind 31880 points

    Hi Amy,

    This thread has been open for a long time. I'm marking it as TI Thinks Resolved, but please follow up if customer needs additional assistance.

    Regards

    Derek Payne