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LMX2492EVM: LMX2492EVM continuous ramp

cleconte
Prodigy 210 points

Part Number: LMX2492EVM

Dear all,

I am currently using the LMX2492EVM Rev C with TICS PRO. My first step to use the board would be to observe continuous sawtooth. I followed the continuous sawtooth example described on $3.2.2 of the LMX2492EVM user's guide. Unfortunately, I can observe one ramp, but it doesn't restart. I verified next ramp was set to '0', and I also verified Register 92, to ensure it was correctly written. I read 0x5C04.

Could you tell me what I need to check, to ensure my ramps will be continuoulsy sent? Thanks for your answer.

Regards,

cleconte

  • 0
    TI__Guru** 121440 points
    Hi Cleconte,

    Could you provide the register setting .txt file or the TICS Pro configuration .tcs file? What is your OSCin clock frequency?
  • 0 in reply to Noel Fung
    Prodigy 210 points

    LMX2492_TICSPRO.zipHi Noel,

    Thanks for your answer.

    Please find attached the registers settings, and the tcs file. Our OSCin frequency is the on board 100MHz.

    Regards,

    cleconte

  • 0 in reply to cleconte
    TI__Guru** 121440 points
    Hi Cleconte,

    Although the on-board VCO can support 10.5GHz but the tuning voltage needed is about 7.5V which is higher than charge pump supply voltage.
    Please try again with 10GHz.
  • 0 in reply to Noel Fung
    Intellectual 295 points

    Dear Noel,

    I have a LMX2492EVM with REV E, populated with  the  VCO of  MACOM model MAOC-009265.

    The highest VCO freq is 9940 Mhz in CW mode, (CPM_THR_HIGH changed from 50 to 63) In Ramp mode I use max of 9900 MHz.

    The lowest VCO Freq is 8860 MHz in CW mode (CMP_THR_LOW changed from 10 to 1), in Ramp mode I use min of 8700 MHz.

    RST flag should be set for continous stable ramping.

    K R 

    Bert

  • 0 in reply to Bert van de Luijtgaarden
    TI__Expert 5370 points
    Dear Bert,

    Noel is on vacation until the 26. I would like your question answered before then.

    I loaded your TCS file and it show frequency selected as start and stop to be outside the range of the Vtune of the device perhaps. Could you try to change these? Otherwise it looks right.

    Regards, Simon.
  • 0 in reply to Noel Fung
    Prodigy 210 points

    Dear Noel,

    Thanks for your answer.

    I remade different tests using the LMX2492EVM, and I can only confirm the following:

    The LMX2492EVM is totally able to generate a ramp up or down. However, the only way I can achieve this ramp, is to check or uncheck the 'FL' box near of the 'RST' box. As a consequence, I can't achieve a continuous ramp. If I don't play with the 'FL' box, the LMX2492EVM stays stuck at a given frequency (start of the ramp, or end of the ramp).

    As I check or uncheck the 'FL', software indicates writing to  '0x00' or '0x40' into register 0x59.

    I used latest TICS PRO, version 1.6.7.0.

    Would you have any explanation about this behaviour?

    Regards,

    cleconte

  • 0 in reply to cleconte
    TI__Guru** 121440 points
    Hi Celconte,

    The FL check box is used to enable Fastlock during ramp. That is, you can use a different charge pump current between CW and ramping. For example, in CW mode, you use a charge pump gain of 10x. During ramp, you can enable fastlock and use fastlock charge pump gain (register R29) of 31x.
    TICS Pro default has set charge pump gain to 31x in CW mode. So, there should be no difference whether you enable fastlock or not.
    Are you ramping between 8700MHz and 9900MHz now? make sure you have set RAMP_LIMIT_LOW_FREQ to lower than 8700MHz.
  • 0 in reply to Noel Fung
    Prodigy 210 points

    Dear Noel,

    Thanks for your answer. I think there is a misunderstood of my questions, linked to the introduction of another user in this discussion.

    My problem is I can't generate continuously a sawtooth ramp.

    My board (LMX2492EVM revC) is able to generate 9.3GHz, and a ramp from 9.3GHz to 10.3GHz. My problem is the only way I could obtain an up and down ramp is to check the FL box, which does'nt seem logical to me at all.

    In the TICS PRO sofware, I indicated to restart on ramp 0, I checked the reset and enabled the ramp.  I tried the VCO  parameters indicated in LMX2492EVM revision D manual (VCO in this manual is the same as in LMX2492EVM rev C), and the ones indicated in LMX24952EVM revision E manual (with MACOM VCO). And I always observe the same strange behaviour.

    Would it be possible for you to make a try with an older version of LMX2492EVM board? And if all is fine, could you send me the registers file? I could then find my mistake, if I missed something.

    Regards,

    cleconte

  • 0 in reply to cleconte
    TI__Guru** 121440 points
    Hi Cleconte,

    your board is RevC, then you should use RevE EVM user's guide because the VCO is from MACOM.
    Can you get the waveform with the exact configuration as shown in section 3.2.2 of the user's guide? If you need to enable FL to get the waveform, this is not expected and I don't have an explanation on this.
  • 0 in reply to Noel Fung
    Prodigy 210 points

    Dear Noel,

    Sorry for the mistake, I have a Rev B board , not a rev C. As a consequence, I have a RFVC VCO on board.

    Would it be possible to have the rev B user's guide?

    I may be wrong, but the only explanation for me, would be there is a mismatch between the rev E  registers  and the  rev B registers.

    As a consequence, when I click on FL, it writes 'Start of ramp'. Unfortunately, I have very recently (last month) bought my board, and I do not know how to  obtain a more recent one.

    Regards,

    cleconte

  • 0 in reply to cleconte
    TI__Mastermind 28031 points
    cleconte,

    The RF VCO1843 covers the same frequency range as the new MaComm VCO. Maybe some differences, but I would not expect this to have a big impact on ramping.

    Checking the FL bit should have no impact, unless the charge pump current on your PLL tab is set very low or tri-state.

    I don't have a copy of the old instructions for Rev B.

    REgards,
    Dean
  • 0 in reply to Dean Banerjee
    TI__Guru** 121440 points

    Hi Cleconte,

    Although I don't think the old user's guide can help you figure out the problem, I attached it here FYI.

    LMX2492EVK.pdf

  • 0 in reply to Noel Fung
    Prodigy 210 points

    Dear Noel,

    Reading this document, it appears that in old revision of the LMX2492EVM, the board is set by default for an external oscillator. The oscillator which is on board, required resistors changes to be connected.

    Everything works correctly, now.

    Regards,

    cleconte