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DS90UB913A-CXEVM: Signal integrity

David Sanchez88
Prodigy 50 points
Part Number: DS90UB913A-CXEVM

Hi,

I'm working on a design with DS90UB913A/914A chips and I have some questions about the signal integrity in their respective eval boards:

  • Parallel data (DIN[0-11] and ROUT[0-11]) in both boards has 10K pull-downs but in the 913's datasheet is indicated: "Inputs, LVCMOS w/ pulldown" and for the 914 they are "Outputs,LVCMOS". Why those pull-downs are necessary??
  • Do this signals need terminating resistors for signal integrity or they are "High-Impedance" pins?
  • For routing, is it advisable to control the impedance of these 100MHz-max signals? 

Regarding bypass capacitors and power supply...there are differences between the "Typical Connection Diagram" of the datasheets and the eval boards, what do you recommend to follow?

I'm not using Power Over Coax.

Thank you and Kind regards,

David

  • 0
    TI__Expert 8055 points
    Hello-
    -There is no need for pull-down resistors on the 913 DIN pins and 914 ROUT pins. It looks like the 10-kohm pull-downs in the EVMs were added as probe points.
    -The LVCMOS signaling relies on reflective switching, so there is no need for any termination resistors. The LVCMOS receivers have high impedance inputs.
    -It is advisable to maintain controlled 50-ohm impedance as the signal transition times may still be relatively fast, depending on the load.
    -Following the "Typical Connection Diagrams" in the datasheets is recommended.

    Regards,
    Davor