This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC38J84EVM: sync to external measurement equipment

Part Number: DAC38J84EVM
Other Parts Discussed in Thread: LMK04828, DAC38J84, ADS54J66

Hi kang,

Than you for your previous help. I've improved the low frequency response of the outputs and I want to check the signal quality over a period of time. Could you please let me know how to connect an external 10MHz reference to the EVM (ie I want to sync with my scope to measure the outputs). I've tried the step lists at page 15 of the EVM manual

"Clock Generator using External Reference The LMK04828 is used a clock generator using an external reference provided to the CLKIN SMA connector (J17). For this option, R177, C206, and C121 should be uninstalled and R185, R186, and C92 should be installed. JP2 can be left open to turn off the onboard VCXO to avoid crosstalk. This option allows a wider frequency range of generated clock frequencies only limited by the VCO frequency ranges of the LMK04828 (see LMK04828 datasheet (SNAS605) for VCO frequency ranges). The possible clock outputs are an integer division of the VCO frequency with a maximum division of 32. PLL1 of the LMK04828 is bypassed in this mode"

but it didn't work. Did I miss anything? The GUI shows errors and all PLLs are out of lock.

Best wishes,

Kelly

  • Kelly,

    You do not need to change any configuration or even EVM component values.

    Whenever you use the DAC38j84 EVM in onboard clocking mode, the dual loop of the LMK will be programmed.  The result is that the first loop will lock onto the 10MHz external reference from your test equipment to create 800kHz PFD for the 1st loop. The whole EVM should be sync with the system.

    Unfortunately we have very limited support for the LMK on this forum. The LMK04828 usage is supported by the clocking team, not data converters team. For additional, more advanced configuration, please post on the clocking forum with respect to the LMK04828.

  • Hi kang,

    Could you please let me know if my following steps are correct:

    Remove JP2, select onboard clocking mode then program LMK04828.

    I've also got a ADS54J66 ADC EVM. Can I configure this EVM to DC coupled mode by removing the input transformers, similar to what I did for the 38J84EVM/

    Best wishes,

    Kelly

  • Hi Kelly,

    Here are some reference designs for the interfacing ADS54j6x family to through amplifiers. This is the best way for DC coupling solution:

    http://www.ti.com/lit/ug/tidubh9/tidubh9.pdf

    I do not support the ADS54J66 directly. Could you please kindly post through another forum post? Other experts will help on this topic.

    I will look into your DAC questions. 

  • Hi Kang,

    I’ll post the question on the ADC related section.

    What is this pdf for? I cannot find useful information in this pdf. I will be really appreciated if you can help me connect my DAC38J84 to an external 10MHZ generated from an oscilloscope, better step by step. I’ve tried different ways, and the waveform on the scope screen is okay, but when I capture the waveform for a longer period of time and do some resampling in Matlab, the results are wrong, so it should be that the EVM and the scope are not synced well.

    Kelly

  • Hi,

    there are two application notes that covers the interface with the amplifier to DC couple to ADC.

  • Kelly

    Kelly said:
    Remove JP2, select onboard clocking mode then program LMK04828.

    Correct. You will also need to input a 10MHz reference signal from you test equipment to J17.

    -Kang