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DAC38RF82: SYSREF interface Between frequency synthesizer and DAC38RF82

Brent Adams
Prodigy 10 points

Part Number: DAC38RF82
Other Parts Discussed in Thread: LMX2594,

Hi,

For our CCA, we are in need TI expertise to define the proper interface and termination for the SYSREF signal between LMX2594 (RFOUTB+/-) and DAC38RF82 (SYSREF+/-).  

This is the last change require before we can finish the design.  This is what we currently have on the DSHRLO schematic. 

  • 0
    TI__Mastermind 24550 points

    Hi Brent,

    It looks like you are wanting AC coupled sysref based on 10nF series caps on output of the LMX. The DAC SYSREF input pins are self biased when AC coupled. You can remove the bias resistors on the SYSREF pins.

    Thanks, Chase

  • 0 in reply to Chase W
    TI__Mastermind 24550 points

    Correcting my previous statement: You can need to remove the bias resistors on the SYSREF pins.

  • 0 in reply to Chase W
    TI__Mastermind 24550 points

    Also, traditionally instead of a 0 ohm resistor (R159) this would be an inductor for dc bias, but if the LMX2594 datasheet says its ok for a 0 ohm resistor then stick with that. From the DAC perspective, any periodic or pulsed periodic sysref through AC caps is ok and will work so long as swing is acceptable. No further components are needed on the DAC side of the AC couple caps. (So remove R152/R153 as mentioned in previous post). If any questions on the LMX output termination structure, you'll have to ask the e2e question for the LMX2594 instead since I am only an expert on the converter itself.

    Chase