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CDCDB800: CDCDB800RSL Clock output VOH level

Thomas O'Donnell
Prodigy 10 points
Part Number: CDCDB800

Tool/software:

Hello, at TI,

What Clock output VOH can be expected for this part on a single pin. 

The spec shows VOH = 225 - 270mV on page 7. 

Is this correct? It seems low.

Thanks,

Tom

  • +1
    TI__Intellectual 1750 points

    Hi Tom,

    The figure of 225 - 270 mV is a figure that is guaranteed by the chip's design and characterization. The output V_OH that you should expect to see on a pin with a load is 660 - 850 mV.

    Thanks,

    Michael

  • 0 in reply to Michael Srinivasan
    Prodigy 10 points

    Hi Michael,  

    Thanks for the info provided!

    Do you know what conditions might cause the device to operate in the 225mV to 270mV range? 

    Wondering if it would it be a lower impedance load, or maybe temperature related?

    Thanks, and Best Regards,

    Tom

  • 0 in reply to Thomas O'Donnell
    TI__Intellectual 1750 points

    Hi Tom,

    The 225-270 mV measurement was a single-ended measurement performed with a DC test load. The 660-850 mV measurement is a double-ended measurement performed with an AC test load. Note, in addition, that the swing can be controlled with a termination resistor, as the output driver format is LP-HCSL (a current based driver).

    Thanks,

    Michael

  • 0 in reply to Michael Srinivasan
    Prodigy 10 points

    Hi Michael, 

    Am I understanding correctly that the 225 - 270 mV is seen on one line to GND, and the 660 - 850mV is a differential measurement between both REFCLK lines?   I am driving this clock into a Microchip PCI1400 which has a V_IH_min of 0.796V so I would expect it not to work at all. It works most of the time, but I feel we may have a VOH vs VIH miss match. VIH min for the PCI11400 is VDD11 - 0.350V. My VDD11 is biased at 1.146V.   We are using the 49.9 ohm REFClk term Resistors also. 

    Thanks for all the help!

    Tom

  • 0 in reply to Thomas O'Donnell
    TI__Intellectual 1750 points

    Hi Tom,

    Your understanding is correct. 

    796 mV is a spec that the V_OH should be able to satisfy (given that it is within the supported range), but could you measure the typical peak-to-peak voltage from that output? If there is still concern about the swing not being great enough, you could increase the value of your termination resistors. 

    Thanks,

    Michael