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LMH0395 - Input Termination

Kawai
Guru 19775 points
Other Parts Discussed in Thread: LMH0395, LMH0384

Please tell me about the input termination resistor value for LMH0395.

The input termination resistor for LMH0395 pin4 (Negative SDI Input) is 49.9Ohm In the datasheet, but if you see the Evaluation Board(User Guide), this resistor value is 37.4Ohm.

Which is the recommended value ?

If 49.9ohm is the recommended value, could you please explain why  this part differs from the other part such as LMH0384 ?

Best Regards,

Kawai

  • 0
    TI__Expert 4400 points

    The recommended termination resistor value for the unused LMH0395 input is 49.9 ohms (per the datasheet), but you could use the typical 37.4 ohms here if you prefer.  The LMH0395 behaves differently than the LMH0384 because it has two output drivers, and using this higher value termination (i.e. 49.9 ohms) on the unused input provides lower jitter at long cable lengths.

  • 0 in reply to Gary Melchior
    Guru 19775 points

    Gary-san,

    Thank you for the answer.

    I understood that 49.9Ohm is the recommended termination resistor for LMH0395 unused input.

    Is there any reason why the Evaluation Board uses 37.4ohm instead of 49.9ohm ?

    From your answer, it seems there is no merit using 37.4ohm.

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Expert 4400 points

    The LMH0395 evaluation board was designed before we optimized this input termination circuit, and we will use 49.9 ohms for the unused input termination in future revisions.

    You really would be okay using either resistor value as the jitter is only slightly reduced when using 49.9 ohms vs. 37.4 ohms for this unused input termination.

  • 0 in reply to Gary Melchior
    Guru 19775 points

    Gary-san,

    I understand.

    Thank you very much.

    Best Regards,

    Kawai