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Using A Pair of DS30BA101 For Fast Bidirectional LVDS

Gary Allen1
Prodigy 30 points
Other Parts Discussed in Thread: DS30BA101, LMH0303, DS15BA101

Hello, I need to implement a bidirectional LVDS to pass a 1pps signal with 500ps timing accuracy.  I am considering using a pair of DS30BA101 devices to do this. (Note I tried using typical MLVDS buffers, but their device propagation delays are too large).  The problem I'm facing with the DS30BA101 is that its outputs cannot be tri-stated.  So, to solve this problem, I am considering using a logic-controlled power switch to shutoff the buffer which won't be used for a given direction flow.  In order for this to work, I need the output stage of the driver to go into high-impedance when the power is shut off.  Does anyone know if the DS30BA101 output stage goes into high Z (10K or higher) when the power is shut off?

Thanks, Gary A.

  • 0
    TI__Expert 3175 points

    Hi Gary,

    There is a similar part LMH0303 that you can turn the output off with a logic control pin 6.

    However, the output stage is an open collector CML output. An external 50 or 75 ohm termination resistor is connected from output pin to VCC, so turning off the output stage, you still have the termination R.

    regards,

    TK Chin

  • 0 in reply to T.K. Chin
    Prodigy 30 points

    TK,

    Thanks for your response.

    I donot think that I can use the part that you specified.  I need a dumb buffer because I won't always have the ability to control the buffer via the SMBus.  Also, the datasheet for this part does not explicitly state the propagation delay between SDI and SDO.

    What about my original question?  Will the DS30BA101 output stage goto hi-z if its power is removed?  Can you let me know the answer to this ASAP?

    Another question related to the DS30BA101 buffer: I was assuming that the propagation delay through this 3.125Gbps buffer is smaller than the propagation delay through the 1.5Gbps buffer (DS15BA101).  However, I now see that the datasheet for DS30BA101 does not specify the device's propagation delay.  Am I making a mistake to believe that the DS30BA101 buffer propagation delay is smaller than the DS15BA101 buffer?

    Also, please let me know if TI has another buffer that I might be able to use.  I need something with propagation delay less than 1ns, preferably less than 600ps.  I also want a dumb buffer, with no need to control settings through a SMBus.

    Regards,

    Gary A.

  • 0 in reply to Gary Allen1
    TI__Expert 3175 points

    Hi Gary,

    When DS30BA101 is powered off, the outputs are high impedance.

    DS30BA101 belongs to the same product family as LMH0303, so I expect pin 6 can be used to enable or disable the output.

    LMH0303 can be use at pin-mode, control bus is optional.

    Propagation delay is not scaled with data rate, so I do not expect you will have less delay at higher speed.

    regards,

    TK Chin

     

  • 0 in reply to T.K. Chin
    Prodigy 30 points

    TK,

    Thanks for your prompt reply.  Given that the buffer output does behave as high-impedance when power is shut down, I think that we are going to use one of the buffers from this family.  We will try using the DS15BA101 device, since it has a documented propagation delay in the datasheet (1.35 ns worst case).  This is the best propagation delay performance, so far, that we have seen for an LVDS buffer capable of driving long cables.

    Thanks again for your help.

    Regards,

    Gary A.