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SN65LVDM176 max data rate?

Robert Sefton
Prodigy 80 points

The feature list in the data sheet says this device is rated for 400Mbps operation, but Figure 17 (transmission distance vs. rate) indicates that it can't operate anywhere near 400Mbps at at distance. In fact at 10m the rate is limited to between 4-5Mbps at 5% jitter and between 20-30Mbps at 30% jitter.

Is Figure 17 accurate for M-LVDS transmission or am I misinterpreting the information?

Using rise time to estimate maximum data rate (minimum bit period = max rise time/0.30), the max rise time for this part is 1ns, which equates to a max data rate of 1/(1ns/.30) = 300Mbps. In my application I need about 50Mbps over a cable distance of 30m. And we need the fail-safe feature of the receiver.

Any comments or advice?

Thanks,

Bob

  • 0
    TI__Guru 62910 points
    Hi Bob,

    Sorry for the confusing data. Figure 17 does look like a reasonable guideline to me, although it should be noted that it is for a specific cable type and may not be broadly applicable for all M-LVDS applications. For these simpler transceiver devices, the performance over longer cable lengths tends to be more a function of the cabling than the transceiver. For your case of a 30-m cable span, what cable type are you planning to use? Do you happen to have any performance specs for it such as scattering parameters or an insertion loss profile? (Or, do you have an estimate of the loss you can expect at 25 MHz?)

    I also wanted to point out that the LVDM176 is actually not an M-LVDS-compliant device. The devices we have with the "LVDM" prefix were developed with the goal of supporting multi-point applications prior to the development of the TIA/EIA standard. (They are very similar to normal LVDS, just with the output current doubled in order to support dual termination.) Once the M-LVDS specification was finalized, we released a family of transceivers with the "MLVD" prefix. For a compliant M-LVDS half-duplex transceiver with failsafe functionality, you can refer to MLVD204A.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Prodigy 80 points
    Thanks for the reply, Max. I'm working as an FPGA consultant on this project and have not seen detailed specs for the cable yet. But the cable in Figure 17 of the LVDM176 data sheets sounds like cat5e and I assume ours will have similar specs, although I believe it is shielded. I'll follow up with my customer.

    Thanks again,
    Bob