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LMH0302 SDO complement output
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 ?
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.
Many thanks for this !
We are now considering some changes to the PCB as well.
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.
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.
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