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DS25BR440: Clarification on Datasheet Specs

Mitchell
Expert 4915 points
Part Number: DS25BR440
Other Parts Discussed in Thread: DS10BR150,

Hi Team,

My customer is looking to use the DS25BR440 and DS10BR150 to drive across a 7 meter PCIe cable rated at 3.125GHz and has a couple questions:

1)      Can they use AC coupling after the driver, or between two drivers at either end of the cable?

    1. The DS25BR440 data sheet on page 11 (Output Interfacing) says DC coupling is OK on the output, but doesn’t mention AC coupling.  Does this exclude using it? Why?

2)      Would you recommend using the part at each end of the cable?  We think maybe the equalization function is better used at the driver to handle PCB board trace differences, and may not be needed to handle cable input differences.  What do you think?

3)      On the DS25BR440, what is the supply current and/or power saved by powering down each individual channel?

Thanks,
Mitchell

  • 0
    TI__Guru* 93670 points
    Hi Mitchell,

    Please below note comments to your questions:

    1). They can use AC coupling either on input or output or both.
    a). This can be AC coupled as well. Please note figure 5 through 8 of the data sheet uses AC coupling on both input and output for different measurements. So the device has internal common mode bias that handles these scenarios.

    2). It would be a better idea to use a single device and position it in such a way to compensate for the loss on input and at the same time pre-emphasis could be used(if needed) in order to meet the overall insertion loss requirements. Also, please bear in mind, normally receiving device at the output of the DS25BR440 may have some equalization as well. In this case, it is better to let BR440 do all the heavy lifting on it's input with minimum or no de-emphasis on it's output- allowing the receiver to do some work as well.

    4). Individual power down powers down output driver and signal detect is on. You would get about 10mA for the driver power saving.

    Regards,,nasser