The TI E2E™ design support forums will undergo maintenance from Sept. 28 to Oct. 2. If you need design support during this time, contact your TI representative or open a new support request with our customer support center.

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.

DAC3171EVM: Data converters forum

Part Number: DAC3171EVM
Other Parts Discussed in Thread: DAC3171, CDCE62005

Hi,

The schematics of the DAC3171EVM show (on the top left corner following the signals DAC_DACCLKC,DAC_DACCLK,DACCLKC,DACCLKC) a circuit like this:

(this image was adapted from  TI's application report "AC-Coupling Between Differential LVPECL, LVDS, HSTL, and CML" )

But according to the data sheet the input clock  DACCLKP/N is supposed to be LVPECL(self biased). What am I missing? Is this the correct way to couple the clock signal?

Thank you.

  • Joao,

    The circuit shown in the DAC3171EVM should be used if you are using the DAC3171 with a LVPECL clock source. This is a LVPECL to LVPECL interface. The circuit shown above from the application report is a LVPECL to LVDS interface.

    Regards,

    Jim

  • Thank you Jim,

    But my problem is that the circuit shown in the DAC3171EVM schematics is identical to the one shown above. That's why I don't understand. The input of the dac clk should be lvpecl.

    Regards,

    Joao

  • Joao,

    If you look closely at the schematic, the two pull-up resistors have 'DNI" labeled by them. This means "Do not install". The circuits are not the same when these are not installed. The board has options for different types of termination to be used.

    Regards,

    Jim

  • Thanks for the reply,

    I'm refering  to the resistors R66 and R67 (150 ohms) , those don't say DNI. Sorry for not uploading the image from the schematic, I don't know if I can upload it.

    Regards, 

    Joao

  • Thanks for the reply,

    I'm refering  to the resistors R66 and R67 (150 ohms) , those don't say DNI. Sorry for not uploading the image from the schematic, I don't know if I can upload it.

    Regards, 

    Joao

  • Joao,

    These are required for LVPECL. This is what we use on almost all of our EVM's when driving a LVPECL output. See page 16 of the CDCE62005 data sheet.

    Regards,

    Jim  

  • Thank you,

    I get it now. I was making assumptions. My problem actually appeared from comparing the DAC3171 to CDCE62005 since it has internal terminations. I assumed that the lvpecl interface would be similar (even if external). (Which from a differential signal point of view it is.)

    Regards,

    Joao