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SN65LVDS2: Calculations for Rise/Fall Time of SN65LVDS2

Jonathan Nguyen
Expert 4555 points
Part Number: SN65LVDS2
Other Parts Discussed in Thread: SN65LVDS1

Hi,

In the datasheet under the switching characteristics table, you list out the test conditions for your AC measurements. These conditions are 100ohm load with 10pF cap, and list the 10/90 tr/tf typ as 600ps.

How is this number achieved? If following a 10/90 reference level, tr/tf should equal 2.2 Time Constants. Using the test condition values in the formula the rise time is actually 2.2ns in this condition. If 600ps were to be designed for, I believe the cap load should be roughly 2.7pF.

Could you help explain the differences in the datasheet spec and my calculations and see if I am making any mistakes/wrong assumptions?

Thanks
Jonny

  • 0
    TI__Genius 10250 points

    Hello Jonathan,

    Your time constant calculations assume the that the load resistance and load capacitance are in series, which is not the case.  See Fig 13. Also, notice that the RL=100 ohm, CL=10 pF is for the driver, SN65LVDS1.  For the SN65LVDS2 receiver, the condition is CL=10pF.

    Regards,

    Yaser