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SN55LVCP22-SP: LVDS outputs

Yue Wei
Prodigy 20 points
Part Number: SN55LVCP22-SP

Tool/software:

SN55LVCP22-SP is a LVDS output. Can its output be terminated with a 150Ω or a 200Ω load (parallel resistor btw out+ and out- )? I would think so, just double checking.
Based on the datasheet, I interpret its current source (min/max) as 3.4mA_min (255mV/75Ω) and 6.3mA_max (475mV/75Ω) which is not a typical 2.5mA-4.5mA LVDS driver.
I want to size my receiver side VID to 500mV_min, so if I can use a 150Ω, minimum VID would be 510mV (3.4mA*150) which meets receiver spec.
The reason I want to double check is because the ibis model (V/I curve & rise/fall curve) on the TI website only models 100Ω load.

  • 0
    Guru 316780 points

    An LVDS line is unidirectional and should be terminated only at the receiver. An additional resistor is likely to increase the load too much.

    The termination resistor should match the characteristic impedance of the cable or trace. What is it in your application?

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Traces are 100ohm impedance controlled, and the traces are 1.5 inches long. The signal is 50Mhz. The datasheet electrical characteristics assumes 75ohm load, but to meet receiver VID, I would need to increase the load resistance by 2. 

  • +1
    TI__Expert 3170 points

    Hi Yue,

    As Clemens said, your termination resistor should match the characteristic impedance your your transmission line for best signal integrity. For LVDS, the termination resistor is supposed to be 100 Ohms. This device inter-operates with with TIA/CIA-644, meaning it can generate 250mV-450mV across a 100Ohm termination resistor. The electrical characteristics  specify the VOD with a 75Ohm termination resistor. VOD (min) and (max) are not specified for any loads other than 75Ohms so there can be no guarantees beyond using a 75Ohm or 100Ohm termination resistor. Figure 8. shows VOD vs. Resistive load which indicates for 500mV VOD ~160Ohm termination would be needed. Keep in mind that these are only typical values and not guarantees.

    Regards,

    Jack