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SN65LVCP418 Noise Susceptibility?

Joseph Stramaglia99021
Prodigy 135 points
Other Parts Discussed in Thread: SN65LVCP418

All,

Have a customer with an Noise Issue using the SN65LVCP418 AC Coupled to a Quadrex (not twisted pair) Cable to transit DVI signals. The box and hardware of the system is well shielded and the cable connects to the main board through a transformer for lightning protection.

When an RF noise source is present near the cables (a standard test) the DVI signal is disrupted.

There doesn't appear to be a CMRR rating on the data sheet and doesn't appear to be enough information to derive it.

Any information you could provide on the CMRR would be greatly appreciated.

Joe Stramaglia - Avnet

  • 0
    TI__Expert 7055 points

    Joe,

    If you take a look a the data sheet, figure 1 shows the ESD structure for the device.  If there is RF energy being conducted into the input pins at a frequency and energy level that is significant, those ESD diodes can rectify the noise to DC and cause a level shift.  I understand that the cable is sheilded, but I think the next best step is to try to quantify how much RF energy is getting into the signal path.  I suspect it is orders of magnitude higher than intended.

    As for CMRR, I don't see it in the data sheet either.  I think that CMRR will be largely dependent on the match between RT(SE) looking into the inputs.  If you have a board handy, it might be fastest to measure the resistance of the SN65LVCP418.  That way you'll also know how closely it matches in your exact test.

    Thanks,

    Jake