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LMX2594: Lock Failure

Oliver McConnell
Prodigy 160 points
Part Number: LMX2594

I have implemented two LMX2594 devices into a design and on multiple boards this works, but one board is failing where one of the LMX devices fails to lock. I have verified that all the passive components on the loop filter seem to be correct. All power pins have been probed and a steady 3.3V is getting to every power pin, we can communicate with the device via I2C and read and write registers, but I have noticed that all the bias voltages (pin, 3, 27, 29, 33, 36, and 38) are either a very low voltage that is not correct, or they are 0V. I cannot find any shorts to ground on any pins and I cannot figure out what could cause this type of failure. I need help understanding what would cause these bias voltages to be so incorrect and cause the part to be dysfunctional.

  • 0
    TI__Genius 11900 points

    Hello Oliver,

    What power consumption do you see?

    When you write POWERDOWN = 0 or POWERDOWN = 1 what do you see?

    Have you tried replacing the device or swapping devices on two boards to see whether the issue is with the board or device?

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Prodigy 160 points

    I don't have a method of measuring power consumption for that chip on this board. Are you suspicious that it is not fully powering up? I have tried replacing the device once and the failure is the same. What should be required for the device to begin showing correct voltages at the bias outputs?

  • 0 in reply to Oliver McConnell
    TI__Genius 11900 points

    Hello Oliver,

    So the boards are identical and the replacing the device did not help? Is this correct?

    The DC voltages of each of the pins are listed in section "9 Power Supply Recommendations" of the datasheet.

    Can you check to make sure you follow the recommendations listed here.

    You mentioned your SPI is working how do you know this? Are you able to see a difference in the chips behavior?

    If the bias pin voltages are 0 I suspect that part is not powered up.

    Thanks,

    Vibhu