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LMX2492 Reference Waveform

Michael Holyoak
Prodigy 120 points
Other Parts Discussed in Thread: LMX2492, CODELOADER, USB2ANY, TXS0108E

Hello,

What type of reference waveform is the LMX2492 expecting for its OSCin input i.e. square and/or sinusoidal?

Cheers,

Mike

  • 0
    TI__Genius 10320 points
    Hi Mike,

    Phase noise and spurious performance are directly related to the input clock edge rate, so typically square waves are recommended. Clipped sine waves are often used as well from signal generators using a limiter.

    Gabe
  • 0 in reply to Gabe Ayala
    Prodigy 120 points

    Hi Gabe,

    What is the purpose of the CE pin - the datasheet does not clearly state this i.e. does this serve as a chip select line (or is that the LE), and if it just for enabling the device, is this pin active high or low?

    Thanks,

    Mike

  • 0 in reply to Michael Holyoak
    TI__Mastermind 28021 points
    Mike,
    It's really not that exciting. It is just for enabling and disabling the device, that can already be done through software. In some applications, a pin might be desirable if you want to link it to other devices that also power down at the same time, like the VCO
  • 0 in reply to Dean Banerjee
    Prodigy 120 points

    Understood, but is the device enabled high or low?  And, which takes precedence - the hard or soft configuration?

    Thanks!

    Mike

  • 0 in reply to Michael Holyoak
    Prodigy 120 points

    Hello,

    I am still waiting on feedback from my previous question.

    Also, how do I configure register readback on the MUXout pin?  The datasheet says readback can be configured on the MOD, TRIG1, TRIG2 and MUXout pins.

    Thanks,

    Mike

  • 0 in reply to Michael Holyoak
    TI__Mastermind 28021 points
    The software takes precidence. POWERDOWN field can be set to powered down, powered up, or determine state based on CE pin.

    For readback, set:
    MUXout_MUX = "Output Readback"
    MUXout_PIN = "Output P-P"

    Then the idea is to connect the MUXout pin to pin 3 of the USB2ANY header, but the problem is that readback in codeLoader DOESN'T WORK.
    This is why I discourage customers from using Readback as the first step of debugging. Sure, you can still read back with an oscilloscope, but this is a lot of effort.

    I am planning to release the TICSPro software to the web this Friday (probably show up sometime next week) and the readback does work for this, so that is the long term solution. Currently, the web version of TICSPro does not have the LMX2492.
  • 0 in reply to Dean Banerjee
    Prodigy 120 points
    Hi Dean,

    First off, I am not using the demo board/codeLoader; I am using a custom board with the LMX2492 as part of a mmWave synthesizer circuit. According to the device's datasheet, the POR value for the MUXout_MUX is what it should be (Table 7) - correct me if I'm wrong. Regarding the MUXout_PIN .. what do you mean by "Output P-P" .. are you referring to Value 2 from Table 6 (Pullup / Pulldown Output? This pin is first being routed into a level translator (TXS0108E), and then into a CPLD pin. Prior to the level translator, does the physical MUX pin require a pull-up resistor of some sort?

    I am also trying to understand the proper write/read sequence for the device. It appears I can write to it by toggling the CE and RESET bits; however, I am not able to lock my VCO, so I am not completely sure that all bits are being written correctly.

    Does the device need to be programmed in a particular sequence? I cannot find any information on this in the datasheet.

    Do you have a direct line I could reach you at? This is rather pressing for my program schedule, and this online post is a bit inefficient.

    Thanks,
    Mike