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DS10CP152: output levels

chris nash
Prodigy 20 points
Part Number: DS10CP152

struggling to decide whatthe actual output level for this device is OUT+ / OUT-

data sheet specifies in LVDS output DC specification

VOD            Differential Output Voltage     min 250 typ 350 max 450 mV

however if i look at the figure 8

this seems to suggest typical  2x380 mV differential voltage.

I will be driving an ac coupled 100 ohm load.

Could you explain this for me

best regards

Chris

  • 0
    TI__Guru* 93670 points

    Hi Chris,

    LVDS output sources - similar to other LVDS devices- about 3mA. This current gets sourced from one end of the driver(P or N) and then it gets dumped into other end(N or P). So 3mA times 100 ohm and this should be about 300mV. I am thinking maybe in this scope shot volt per division is incorrect.

    Regards, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser thanks for this quick reply. My own measurements suggest similar but  would the true differential output range perceived at an input be doubled ?This is important for me as i am driving an sfp module and the minimum input level is quite high.I would appreciate your thoughts on this as i believe the spec is talking about a single ended voltage range of one signal

  • 0 in reply to chris nash
    TI__Guru* 93670 points

    Hi Chris,

    It will not be doubled. LVDS driver is a limiting device. Meaning the output is either one or zero. The output driver is limited to about 3mA source so the output differential swing is limited to about 300mV.

    Regards,Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi nasser, the doubling i was referring to is at the receive device differentially perceived between its two DIN+ and DIN- pins. I am looking into what devices the part can drive so clear distinction between what you are describing as a single ended voltage, i believe falsely labelled as differential in the data sheet

  • 0 in reply to chris nash
    TI__Guru* 93670 points

    Hi Chris,

    Understood and thanks for the comment.

    Regards, Nasser

  • 0 in reply to Nasser Mohammadi
    Prodigy 20 points

    Hi Nasser thanks for the reply.. if you dont mind me extending this question a bit. The reason for asking is that i am using this mux to link a gigabit data stream to an sfp optical transceiver. This device has kind of a weird input spec for the differential data. I would appreciate a second opinion  whether the ds10cp152 has enough level to drive the sfp. This is all very much down to how you interpret differential voltage levels specs in the datasheet. The solution seems to work fine but have started to get occasional dropouts. This may be due to other elements in the system.

    Your opinion would be appreciated.

  • 0 in reply to chris nash
    TI__Guru* 93670 points

    Hi Chris,

    Whether CP152 drive level is good enough for the SFP module depends on the minimum input receive level for the SFP module.

    Recommendation is to check your SFP minimum input swing level. Please check your SFP minimum input swing level to make sure it can meet minimum output swing level of CP152(~250mV).

    Regards, Nasser

  • +1 in reply to Nasser Mohammadi
    Prodigy 20 points

    ok many thank...