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multiple LMX2581E Eval boards operation

Youngho Suh
Intellectual 540 points
Other Parts Discussed in Thread: LMX2581E

Hi,

I would like to use LMX2581E eval board around 8 units for generating different output frequencies for my system. I found in manual, I can set output frequency through computer interface. If I want to set frequencies for 8 different eval boards, what is the best way? Can I program unit by unit by plug/unplug in interface connector to each board? Or, as soon as I unplug it, will it lose program information? Would you please recommend what is the best way to operate multiple LMX2581E units? FYI, my application does not need to turn on the signals simultaneously.


Second question is, do you have any DDS (Direct digital synthesizer) for ref clock in? My application may need some fine number of ref clock such as 5.xMHz, 5.yyMHz, or 5.zzzMHz. So to implement that, I may need DDS rather than XVCO.

Thanks in advance.


Youngho

  • 0
    TI__Mastermind 28021 points
    Youngho,
    The simplest thing to do is to program one device and then unplug the header and then plug into the next device. The LMX2581E does have a CE pin and BUFFEN pin, but you can configure the software so that these pins have no impact. If you do this, you do not lose program information or power down when the cable is disconnected.
    If you try to share lines, then you need a separate LE signal to each device, which is harder than the plug/unplug method. Also, if you want to program a device and don't want noise to accidentally program it, you can use the uWireLock bit which will ignore all further programming to the device, except reading back and programming this uWireLock bit.
    Regards,Dean
  • 0 in reply to Dean Banerjee
    Intellectual 540 points
    thank you so much. I will try plug/unplug for programming.
  • 0 in reply to Dean Banerjee
    Intellectual 540 points
    I could successfully program 4 different LMX2581EVMs with 4 different frequencies using uWireLock bit as you recommended. I have another issue with external 10MHz reference sync. Now, I am using external 10MHz by reconfiguring EVM board registers as described on user's guide section 3.3 "OSCin Input". It performed well and verified with spectrum analyzer. Originally I was using four signal generators to provide sample clocks to ADC and sync'ed with 10MHz reference signal (all systems are synced with it). Now, I replaced signal generators with four LMX2581EVMs with external 10MHz reference. I assumed this would sync with other signal generator and DRO in the system as it worked with signal generators. BUT found data are very crappy and it seems not syn'ed. I replaced back to signal generators and found data returned to good one. Can you explain what is going on? I expect if we have the same 10MHz reference, all LMX2581EVMs and other signal generator and DRO should be synced. Would you please let me know your suggestions for the next steps?
    Thanks, Youngho
  • 0 in reply to Youngho Suh
    TI__Mastermind 28021 points

    Yongho,

    I can't be sure, but check out section 3.3, page 11 of the operating instructions.   I have found that if you use the on board XO, this works great, but with a signal generator, change component L3 to a 0 ohm resistor and the performance improves.

    It might depend on if the signal generator shares the same ground with the power supply on your bench setup.  Maybe this is what is going on.

     

    Regards,
    Dean