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SN65DSI85 termination resistor

Ryuuichi machida
Guru 12640 points

Hi,

I would like you to confirm which case 200 ohm near end termination(can be set ADD 0x1A[1:0] CHA(B)_LVDS_TERM) should be used.

In my understanding, general LVDS differential line should be traced as 100 ohm. so termination resistor should be used 100 ohm.

However, default register values of ADD 0x1A[1:0] CHA(B)_LVDS_TERM are set to "1" (This means 200 ohm near end termination is set).

So, could you please confirm whether these register values should be set depending on characteristic impedance(also termination resistor of LVDS receiver) or not ?

I'm not sure which case 200 ohm near end termination should be used...

Best Regards,

Machida 

  • 0
    TI__Mastermind 18655 points

    Hello Machida, 

    The field you mentioned (CHA_LVDS_TERM )  and CHA_LVDS_VOD_SWING control the differential output voltage as stated in the Flat Link Output table in the device datasheet.

    I would recommend using CHA_LVDS_TERM - 0 – 100Ω differential termination and follow the guidelines described below:

    Route together with controlled differential 100ohm impedance and controlled single ended 50ohm impedance. Keep away from other high-speed signals especially all FlatA/FlatB* signals. Keep lengths within 5mil of each other. Keep traces on layers adjacent to the ground plane. Keep the number of VIAS to minimum. If VIAS used, make it symetrical through all signals. Keep diff pairs separated at least by x3 of the trace width.

    NO STUBS on the signal path, components should be placed such that the signalscan routed in pass-thru manner.

    Regards