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SN65LVDS31: LVDS source resistance measurement

Matthew Matrullo
Prodigy 10 points
Part Number: SN65LVDS31
Other Parts Discussed in Thread: SN65MLVD047

To Whom it May Concern, 

I am currently reading Lit Number: SLLD009 (LVDS Application and Data Handbook) and was looking at the Precompensation in the Adjusting LVDS output levels section and I was curcious how you measured the source resistance on the driver to get 895 ohms? I am currently try to add precompensation on the SN65MLVD047 and wanted to figure out a good way to measure the source resistance of the driver to get a plot like in FIGURE 3-9 of the SLLD009.  Thanks!

  • 0
    TI__Genius 15241 points

    Hello,

    From what I see the value came from the output current vs. output voltage plot from 0.1 V to 1 V. LVDS drivers have a constant current source driving ~3.5 mA, which is close to the “ideal” current source that they mention they measured (~4.2 mA). See Section 8.1 in the datasheet for the measured device (SNx5LVDSxx High-Speed Differential Line Drivers datasheet (Rev. N)) for the definitions of the test circuit timing and voltage definitions for the differential output signal.

    If there is a way to first improve the noise margin in your system, I would recommend looking for way to do that. This would include looking for way to better match stubs, lessen bus loading, eliminate connector mismatches, etc.

    Regards, Amy