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LMH0303: LMH0303 about termination

Diego Shinji Kawaguchi
Prodigy 130 points
Part Number: LMH0303
Other Parts Discussed in Thread: LMH0318

Dear Team,

I would like to inquire about the rationale behind the circuit configuration for the LMH0303, specifically regarding the proper handling of the /SDO terminal (pin 11) in single-ended mode.

I found the following exchange on the E2E forum that discusses this topic:

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/272140/lmh0303-lmh0384-about-termination

 

It was mentioned that in order to balance the differential output driver, the unused output (/SDO) requires termination similar to the true output, while the return loss compensation network (resistor in parallel with inductor)  seemingly has a negligible effect on the active output (SDO).

 

Is this difference quantitative?

And if it is quantitative, are there any simulation or test results that provide insight into why the unused output (/SDO) must be terminated with a terminating resistor and not require a return loss compensation network?

 

I would like to show that the LMH0303 circuit in the single-ended output configuration from the E2E document above is appropriate.

 

Thank you for your assistance and I look forward to your detailed response.

 

Best Regards,

 

Diego

  • 0
    TI__Guru* 93670 points

    Hi Diego,

    It is preferred to have the un-used output to be terminated with the exact termination - including return loss network. This  will provide a balanced AC/DC impedance to both unsed and un-used outputs. However, we don't have a quantitative result for this. Later or more updated cable drivers have these return loss network on both P & N built into the part(please note LMH0318 for example).

    Regards, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 130 points

    Dear Nasser,

    Thank you for your prompt and informative response.
    I appreciate the clarification on the termination of the unused output in the LMH0303 circuit.

    Best regards,

    Diego