SN65LVDS31: Driving 150ft cable

Alec Forbes

Part Number: SN65LVDS31
Other Parts Discussed in Thread: SN65LVDT33

Team-

My customer is interested in using the SN65LVDS31 to drive 20Mhz LVDS lines through a 150ft Cat6 ethernet cable to a SN65LVDT33. The datasheet for the LVDS driver has a chart showing max signal rate for given distances, but it stops at 20m. Could you comment as to whether this device will be able to drive the line capacitance of such a long cable? At 150ft*14pf/ft (nominal for Cat6) we are looking at 2.1nF of cap which is significant.

If it isn't possible, could you recommend either a different device or an alternative solution that would allow my customer to accomplish what he is looking for?

Thanks,

Alec

over 7 years ago

0 Alec Forbes over 7 years ago

TI__Expert 3500 points

Any chance someone could take a look at this today?

Thanks,
Alec

0 Lee Sledjeski over 7 years ago

TI__Mastermind 43795 points

Alec,

At 20 MHz the nominal attenuation within the CAT6 cable will be ~ 4.25 dB for 50 meters. Overall this is about at the limit for non-equalized signaling (LVDS / RS-485 / etc.). If this application is 20 Mbps data, then the attenuation will be less and more robust operation is possible. A warning about LVDS and these very long cables, the common mode voltage of LVDS is limited to +/- 1V. Over 50 meters of cable this is likely to cause issues. I would prefer to use capacitive or transformer coupling to help isolate the driver and receiver.

Regards,

Lee

0 Alec Forbes over 7 years ago in reply to Lee Sledjeski

TI__Expert 3500 points

Lee-

Thanks for the help. It sounds like what you are saying is that there shouldn't be any issues with the high frequency content rolling off due to capacitance, but there will be DC attenuation due to the resistive losses, is this correct? Could you recommend a specific part that might be able to help with this?

Thanks,
Alec

0 Gerardo over 7 years ago in reply to Alec Forbes

TI__Genius 11280 points

LVDS_AppAndDataHandbook_slld009.pdf

Hello Alec,

Please see the attached document that discuss the data transmission basics on LVDS.

Regards,

Gerardo

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SN65LVDS31: Driving 150ft cable