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LMX2594EVM: LMX2594EVM

FRANCESCO FIUME
Prodigy 170 points

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594, LMK61E2,

Object: LMX2594 and LMK61E2 : boards settings problems ---> http://www.ti.com/lit/ug/snau210/snau210.pdf

Greatings,

I'm a student of ‘Politecnico di Torino’ and I'm doing a master thesis using the boards in question. I am writing to you to raise some problems regarding the setting of these boards .

I would like same clarification on how to set up “single ended” mode since this is not clear by reading the information provided on page. 18/36 of the attached pdf.

In addition, it should be noted that the guidelines on how to set up the "differential pair" mode are followed by a scheme concerning the "single ended" mode (pages 17 and 18) and viceversa .

Another doubt to be solved is related to how to carry out the following operations reported in the guidelines (pages 17 and 18):

  • Switch R24b to R24;
  • Must remove R33 to…;
  • Populate R25 and R30;

and what indicates the symbol “X” in red in Figg. 14 and 15 regarding the board LMX2594.

Thanks for your cooperation.   

  • 0
    TI__Mastermind 28031 points

    Francesco,

    The LMX2594 input can be driven 4 different ways:

    1.  Single-ended external oscillator

    2.  Single-ended on-board oscillator

    3. Differential external oscillator

    4.  Differential on-board oscillator.

    Indeed the figure titles for figures 14 and 15are swapped.

    Let's assume that you want to drive this with a single-ended external reference  that you supply.  In this case, set up as in figure 15.

    The steps of switching R24b to R24, removing R33 and populating R25 and R30 are essentially disconnecting and removing the power of the on board XO.

    Now for R25 and R30, think of it this way, you can terminate both sides with 50 ohm, or the other case is to not put these two resistors and put 100 ohm in R32.

    One thing to note that although maybe you only want to drive the OSCinP pin, you still want the impedance as looking out of the OSCinN pin to look similar.  This is for optimal spur performance.

    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 170 points
    Good evening, I would like to have some more clarification on the matter.
    I state that I want to set the synthesizer in such a way that it works as follows:
    -) differential input with internal reference at 100 MHz;
    -) single ended.
    1) Which and how many are the possible configurations of the board 'LMX2594EVM'?
    Example: Internal reference, External reference, Reference taken from the board LMK61 (since it is connected to the board above). How do you enable one rather than the other mode? Please indicate in detail the operations to be performed on the hardware.
    2) What is meaning of 'disconnecting and removing power on the board'? Desolder R33?
    3)Which terminals should the two 50 ohm resistors have to connect? or possibly the one from 100? Indicate the names.
    4) In the case of single output, the RFoutBM, RFoutBP, RFoutAM terminations must all be connected to 50 ohms?
    5) What is the reference that provide the best 'Phase Noise' comparing both 'LMX2594EVM' and 'LMK61E2' boards?
    Regards, Francesco.
  • 0 in reply to FRANCESCO FIUME
    TI__Mastermind 28031 points
    Francesco,

    Comments below:


    Good evening, I would like to have some more clarification on the matter.
    I state that I want to set the synthesizer in such a way that it works as follows:
    -) differential input with internal reference at 100 MHz;

    For this, it is the default setup. OSCinP and OSCinM are hooked up to the XO and there is power to the XO.

    -) single ended.

    There are 4 possible ways to drive this single-ended: (1) Single Ended with external reference through OSCinP, (2) single-ended with on-board reference through OSCinP, (3) Single-ended with external reference through OSCinM, (4) single-ended with on-board reference through OSCinM

    1) Which and how many are the possible configurations of the board 'LMX2594EVM'?
    Example: Internal reference, External reference, Reference taken from the board LMK61 (since it is connected to the board above). How do you enable one rather than the other mode? Please indicate in detail the operations to be performed on the hardware.

    I showed 4 possible single-ended methods. Also you can do differential using the on board XO or differential using an external reference (such as the LMK6100 board)

    2) What is meaning of 'disconnecting and removing power on the board'? Desolder R33?

    Yes. If you don't want to use the on-board XO, you need to disconnect power from it using R33

    3)Which terminals should the two 50 ohm resistors have to connect? or possibly the one from 100? Indicate the names.


    On OSCin, you can put 50 ohm for R25 and R30. Or if you are differntial, you can keep it this way, or instead pull off R25 and R30 and instead place 100 ohm on R32.

    4) In the case of single output, the RFoutBM, RFoutBP, RFoutAM terminations must all be connected to 50 ohms

    Only the unused side of a differential pair needs to be. If you are not using RFoutB, then power it down and don't worry about terminating it. If you are using RFoutAP, but not RFoutAM, then it's best to put a 50 ohm terminator on RFoutAM so both sides look balanced.

    5) What is the reference that provide the best 'Phase Noise' comparing both 'LMX2594EVM' and 'LMK61E2' boards?

    The possibilities are:
    1. 100 MHz Wenzel 501-4623G This is not supplied with the board, but this is what we do for the official datasheet measurements as it is the lowest noise reference we have.

    2. On board XO. This has very respectable phase noise and matches up with the above one at offsets above about a few kHz.

    3. Reference Pro board. This is not the default, but is convenient and certainly better than a signal generator.

    4. Signal generator. Almost all signal generators have terrible phase noise. They are convenient, but can degrade in-band noise as bad as 20 dB.

    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    Prodigy 170 points
    Good evening, I followed all the steps you indicated to me. I set the system in such a way as to have an internal reference at 100 MHz, that means 'single-ended with on-board reference through OSCinP' and single output. The RFoutAM port was finally terminated with 50 Ω and unsoldered the resistance R33 as indicated. There was a problem with the board LM2594EVM. The problem encountered is: shorted Vcc port.
    So, it is not possible to apply any input voltage.
    Is it possible to have support from you on this? Hopefully, can we send it to your team for a damage resolution?
    If so, can we have another new one otherwise I have to stop with my master thesis?
    Thank you so much for your cooperation.
  • 0 in reply to FRANCESCO FIUME
    TI__Mastermind 28031 points
    Francisco,

    Unfortunately, I'm not set up well to service EVMs. Perhaps you can go through the channel you got the EVM and hopefully they know how to better deal with replacing an EVM. TI also has some strict internal policies about shipping EVMs to customers.

    We do test EVMs before we ship and our testing should have caught anything as obvious as a short from Vcc to Ground.
    I would ensure that you are not current limited as this board can draw 350 mA.

    If you think that maybe something got shorted during modifications (maybe created a short at R33), you might want to try to hunt down the short yourself. For instance, if you remove R34, you would disconnect the outputs and if you remove R35, the rest of the circuit.

    Regards,
    Dean