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How to connect LVPECL to DS25BR150?

Bruce Jiang
Intellectual 310 points
Other Parts Discussed in Thread: DS25BR150

Hi.

In my design, the output of SY10EP451 would be connected to DS25BR150. The data rate would be 3.0Gbps, and DC-Coupled mode would be used.

From the datasheet, 150Ohm pull-down to gnd is ok for inputs of DS25BR150.

But for SY10EP451, all the data are measured on condition that the output common voltage is VCC-2V.

So directly 150Ohm mode is ok for SY10EP451?

Thanks.

  • 0
    TI__Guru* 91440 points

    Hi Bruce,

    I think SY10EP451 is not a TI device so please check with the vendor to see if putting 150 Ohm would be okt. I think AC coupling with high value Cap would isolate these two devices common mode voltage from one another and perhaps is a good idea.

    Regards,,nasser 

  • 0
    TI__Mastermind 29635 points

    Hi Bruce,

    I am unable to comment on the SY10EP451, as this does not appear to be a TI part.

    However, if the output signal of the SY10EP451 satisfies the requirements of LVPECL output drivers, then yes, using the drawing shown on Fig. 8 of the datasheet for the DS25BR150 input interfacing should work.

    The choice of 150Ohms depends on VCC. For LVDS signals, a common mode voltage is around 1.2V. Since LVPECL outputs typically already have 50Ohm pull-ups to VCC-2V, you will need to check that the common mode voltage levels will meet the LVDS common mode requirements. For example, 150Ohms should work if VCC =  3.6V, since having (3.6-2) * (150/(150+50)) = 1.2V.

    Please reference various signal type interfacing here: http://www.ti.com/lit/an/slla120/slla120.pdf

  • 0 in reply to Michael Lu (Santa Clara)
    Intellectual 310 points

    Hi, Nasser Mohammadi and Michael Lu.

    Thanks for your advice.