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DAC37J84EVM: Data converters forum

Artem B
Prodigy 30 points
Part Number: DAC37J84EVM

Hi everyone

We are using DAC37J84EVM with removed output transformers with TSW14J56.
On the first picture there's a digital signal that goes to DAC.
On the second picture there's IOUTAP output and on the third picture there's IOUTAN output.
"Compliment Output Data" is disabled for both DACs.
Why are the signals look inverted?






  • 0
    TI__Genius 12850 points

    Hi Artem,

    The output of this DAC is differential, so the IOUTAP and IOUTAN will be 180 out of phase with respect to each other at all times.

    The complimentary output setting will swap the positive and negative halves of the differential output signal per that specified channel. This will allow for easier PCB layout and routing options.

    Regards, Chase

  • 0 in reply to Chase W
    Prodigy 30 points

    Thanks Chase
    But according to signal that I send from FPGA, it looks like P and N should be vice versa.
    Please look carefully at the pictures that I attached.

  • 0 in reply to Artem B
    TI__Genius 12850 points

    Artem,

    This is likely due to the layout on our EVM. I imagine the balun is what is causing the polarity inversion. Do the signals swap if you toggle the complimentary output bit for IOUTA?

    Thanks, Chase

  • 0 in reply to Chase W
    Prodigy 30 points

    Yes, they do. Just wanted to know if it is the correct DAC behavior.

  • 0 in reply to Artem B
    TI__Genius 12850 points

    I imagine the DAC itself is functioning fine and the balun is causing a 180 phase shift. Can you probe on each side of the balun to confirm if the hardware is causing this inversion?

  • 0 in reply to Chase W
    Prodigy 30 points

    As I said, we removed all the transformers from the schematics, because we needed DC, so I don't have the baluns on the board. So that's the DAC outputs themselves. If you can measure the signal before and after baluns and send me the results, that would be great.

  • 0 in reply to Artem B
    TI__Guru* 91957 points

    Artem,

    I just checked this on our EVM and you are correct, the signals are inverted. I am checking with design to see if it was designed this way or maybe the ball assignment is incorrect in the data sheet.  Are you seeing this on all four channels? 

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 30 points

    Hi Jim, thanks for your attention.
    Yes, they look inverted on all four channels.

  • 0 in reply to Artem B
    TI__Guru* 91957 points

    Artem,

    The designers that worked on this part are no longer part of our group. Due to limited resources it may take awhile to find out if this is truly an issue with the data sheet. For now, if these signals need to be swapped on your application, I can only suggest to use register 0x01 bits 4:7.

    Regards,

    Jim