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Original question:

LMK00338: Vcross doesn't meet PCIe gen5 spec

LMK00338: Vcross(min) of LMK00338 HCSL Output Doesn't Meet VCMD(min) of LMK00334 CLKin0 Input

Rob Weinstein
Prodigy 10 points
Part Number: LMK00338
Other Parts Discussed in Thread: LMK00334

Tool/software:

Hello,

My design uses an HCSL output from a LMK00338 to directly drive the CLKin0 input of a LMK00334 and, at first glance, the common-mode voltage ranges seem incompatible.  Here's what I have:

Are the LMK00338's HCSL outputs compatible with the LMK00334's CLKIN0 inputs without AC coupling capacitors?

Thanks,

Rob

  • 0
    TI__Intellectual 2630 points

    Hi Rob,

    HCSL is a current-based driver, so you can adjust your voltage ranges simply by adjusting the value of your shunt terminations. Currently, the values are 50 Ohms, but you can increase the value of your crossing voltage by increasing those values (i.e. with 100 Ohm shunt terminations, your swing/crossing voltage will be doubled). With this tweak, you should not need an AC coupling capacitor for the LMK00334 inputs. Hope this helps.

    Thanks,

    Michael