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Can the VAC_REF on the CDCLVD2102 drive x4 50-Ω transmission lines?

Michael Raleigh
Expert 3245 points
Other Parts Discussed in Thread: CDCLVD2102

Hi,

I can see in the data sheet for the CDCLVD2102 that its "specifically designed for driving • One Input Dedicated for Two Outputs 50-Ω transmission lines. If driving the inputs in single • Total of 4 LVDS Outputs, ANSI EIA/TIA-644A ended mode, the appropriate bias voltage (VAC_REF) Standard Compatible should be applied to the unused negative input pin." But I'm not seeing an indication of how many lines. In the LVPECL to LVDS example (figure  18) it shows 2 50-Ω lines, can it handle 4?

Thanks,

  • 0
    TI__Mastermind 32575 points
    Vac_ref is intended for biasing AC-coupled inputs through 50-ohm termination resistors, or biasing the unused input (INNx) in single-ended/LVCMOS input configurations. Vac_ref spec provides the output voltage rating under 100 uA load.

    The device only has 2 input pairs. If INP0 and INP1 are driven single-ended with 2.5V LVCMOS input, then INN0 and INN1 can both be connected to Vac_ref to set the input buffer threshold to 1.25 V (nominal). Each INNx input has +/-10uA leakage current, so Vac_ref can easily drive both INN0/INN1 inputs and stay within the Vac_ref output specification. It is recommended to use 0.1 uF bypass cap on Vac_ref.

    Regards,
    Alan