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LMH0302 SDO complement output

Petros Matsakos
Prodigy 20 points
Other Parts Discussed in Thread: LMH0302

Hi,

We're using an LMH0302 as cable driver in an application requiring just one output and have connected the true SDO output according to the

Does the SDO complementary pin need to be pulled up with 75Ohm or can it be not connected ?

Regards

Petros Matsakos

  • 0
    Prodigy 10 points

    Hi

    See Application note National:AN-1972 TI:SNLA118B "Board Layout Challenges in Serial Digital Interface" .

    "75Ohm Pull-up&75Ohm Terminate" is being explained with this application note.

    Regards.

    Shigetaka Furukawa

  • 0 in reply to Shigetaka Furukawa
    Prodigy 20 points

    Hi,

    Many thanks for this !

    We are now considering some changes to the PCB as well.

    Thanks

    Regards,

    Petros Matsakos

  • 0 in reply to Petros Matsakos
    TI__Expert 4400 points

    As suggested, SNLA118B: Application Note 1972 "Board Layout Challenges in Serial Digital Interface" shows the proper schematic (Figure 6) and also a good suggested PCB layout (Figure 7) for the LMH0302 SDI cable driver with one active output.

    http://www.ti.com/litv/pdf/snla118b

    The unused output (SDO-) is the complement to the used output (SDO+), and so it should be terminated similarly to the true output to ensure that the differential output driver is balanced.

    To accomplish this, the unused output should have the 75 ohm pullup resistor, followed by the AC coupling capacitor, then followed by a 75 ohm resistor to ground.  This way, both sides of the driver see the same termination DC-wise and AC-wise (during transitions).  The return loss compensation network (resistor in parallel with inductor) is not necessary on the unused output.