I'm designing MLVDS interface.
Want to use sn65mlvd047a driver.
Using multi-drop -- 1 driver 8 receivers.
The '047a spec requires 55 ohm max load resistance.
The TI paper slla038b says multi-drop only needs 1 load resistor at end of line.
Characteristic impedance requires 100 ohm.
Only way I see to satisfy this is to terminate at each end of PCB transmission line even though multi-drop is supposed to have only 1 load resistor.
Please advise me on this
You are right that using dual termination is the correct approach for this application. The reason for this is that the MLVD047A device was designed to support the M-LVDS standard. M-LVDS devices need to be able to handle multi-point topologies (i.e., multiple drivers and receivers on a bus), and as a result must be able to support termination at either end of a transmission line. If it were an LVDS part instead it would make sense to use single termination.
Besides the extra resistor, there shouldn't be any downside to using double termination for a multi-drop application. In fact, the source-side termination should help reduce any reflections that may be directed towards the transmitter from the receiver stubs.
Best regards,Max RobertsonCommunications Interface Applications(214) firstname.lastname@example.org
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