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LMX2594EVM: Problem with the channel divider

user3764392
Prodigy 60 points

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594, LMX2582

Hello there,

I got this evaluation board and after some initial problems its now working, but I cant get any output frequency below 156.25 MHz. The cause for that is, if I set divider SEG3 to more then 1, I got no signal anymore. I´ve reseted the device and programmed it again, but that has changed nothing. Am i doing something wrong?

Regards

Alex

  • 0
    TI__Mastermind 28031 points
    Alex,

    I see a few possibilities:

    1. Bad RF connector center pin soldering
    Try another connector and ensure that this is the same for all. We had a batch of boards with the RF center pin not soldered well on all connectors. At higher frequency, it was OK due to parasitica capacitance between board and pin, but low signal at low frequencies.

    2. Bad Programming
    In the LMX2594, you can not program SEG3, although it does calcualte this value. Ensure that you are not using the LMX2582/92 software as the programming of the channel divider is different.

    3. Max Divide violation
    You can not use a VCO divider greater than 8 for a VCO frequency greater than 11.5 GHz.

    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 60 points

    Hey Dean,

    I´ve heard about the problem with bad soldered center pins, but this is not the problem in my case because this would lead in a 3 dB ramp from DC to any cutoff  frequency and would effect the noise floor too. Max Divide violation also is not the case. I´ve raed the datasheet of LMX2594 and Table 8 tells about frequency limitation and at the moment I´m working with 7.5 GHz. The same table shows the values of SEG1 - SEG3. What I mean is not to programm SEG3 seperatly, but as I switch from a equivalent division value of  48 to 64, I got no more output. And the same for all greater values. With switching from 48 to 64 SEG3 goes into the chain and is not bypassed anymore. For me it looks like there is an issue with this stage. Please tell me, how we can handle this problem.

    Regards,

    Alex

  • 0 in reply to user3764392
    TI__Mastermind 28031 points
    Alex,
    The LMX2594 output divider has been thoroughly tested over all divides and we have seen no issues.
    Here's what I would say:

    1. A long time ago, we had an error in TICSPro with the wrong divides in the drop down box and the values were off, but this was fixed.
    2. When you switch to the higher divide, is it possible there is a slight current increase and you are current limited, or the some issue to one of hte power supply pins.
    3. Could this be some software issue. In TICSPro, go to the Default Configurations and choose "Default Mode 2017-3-22". This will change some frequencies around that you can change back, but also it resets many test/engineering bits. Maybe one of these is powering down segment 3.
    4. Are you in SYNC mode? The IncludedDivide changes between 48 and 64 Maybe wrong output frequency if you have an older TICSPro.

    How many devices do you see this on?


    Regards,
    Dean