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LMX2572LPEVM: On-board crystal oscillator not working

Amrita Kothari
Prodigy 40 points
Part Number: LMX2572LPEVM
Other Parts Discussed in Thread: LMX2572

Tool/software:

Hi all,

We are trying to use the TI LMK60E2-100M00SIAT to provide 100MHz reference clock for our EVM board. We soldered the IC on to the board by following the connections provided in the datasheet. Attaching the screenshot from the datasheet below

                                                                                                         

The above design, however, is not working as we aren't getting any output. Kindly let us know if the chosen IC is the right one or if we are missing anything in the set-up.

Thanks in advance,

Regards,

Amrita

  • 0
    TI__Guru* 98400 points

    Hi Amrita,

    LMK60E2 is a LVPECL oscillator, you should do the following modification.

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Hi Noel,

    Thanks a lot for the reply. Before making the changes, want to confirm that:

    1. resistors 26 and 31 need to be replaced with 0.1uF capacitors

    2. need to connect 150ohm resistors for 7 and 28.

    can you confirm this once ?

    Thanks again.

    Regards,

    Amrita

  • 0 in reply to Amrita Kothari
    TI__Guru* 98400 points

    Hi Amrita,

    That is correct.

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Hi Noel,

    I made the above changes to the circuit and on giving the signal config through SPI from PRO board, i see that the LMX board is getting shorted. Voltage is dropping to 2.8V. Continuity and short circuit checks were done across the newly soldered components and things seemed fine.

    Kindly let me know if we can find out why is it not working or we missed something.

    Thank you.

    Regards,

    amrita

  • 0 in reply to Amrita Kothari
    TI__Guru* 98400 points

    Hi Amrita,

    Did you provide enough current to the board, the oscillator may consume up to 110mA. 

    Can you identify if the short is due to the synthesizer or the oscillator?

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Current limit was set to 0.1A. When I use the default config which is single tone output, there is no short even though the frequency is shifted to 1.8GHz instead of the programmed 1.5GHz. So I think the oscillator is causing the short.

  • 0 in reply to Amrita Kothari
    TI__Guru* 98400 points

    Hi Amrita,

    100mA current limit is too small. LMX2572 already consumed 75mA. Try again with current limit set to 500mA.