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DS125BR111: Recommended solution and Placement.

Jim CHEN
Expert 4795 points
Part Number: DS125BR111
Other Parts Discussed in Thread: DS100BR111, DS100BR210

Dear Team,

This is a storage server application. My customer would like to find a 2 lanes SAS-3 redriver for this project (1 lane TX and 1 lane RX).

Below figure shows the structure of the server.  I found DS125BR111 that maybe could meet their requirement and suggest them to put the redriver at the black square location in the figure.  

But the customer thought that the total channel loss is about 31 dB from the redriver to HDD connector. 

PCB trace 500mm = 20dB loss

200mm MiniSAS cable = 3dB loss

PCB trace 200mm = 8dB loss

20+3+8=31 dB channel loss.

 It sees like DS125BR111 (up to 10dB EQ gain) cannot handle such long trace. 

So my questions are:

1.  Do we have any other suitable solution?

2. Or could we put multiple linear redriver in series? 

3. Do you have recommended placement for redriver? 

Thank you.

  • 0
    TI__Mastermind 43795 points

    If you want to use a higher gain device I would use the DS100BR111 or DS100BR210.  The DS100BR111 or DS100BR210 can only be placed so that most of the channel loss is on the repeater input side.  They will not work in this application if placed closer to the SAS-3 Tx.

    You can also try the DS125BR111 instead of the DS100BR111, it can usually work up to ~ 34dB of loss.  The SAS-3 drive and HBA on the motherboard should be able to handle ~ 24dB all by themselves.

    Regards,

    Lee

      

  • 0 in reply to Lee Sledjeski
    TI__Expert 4795 points
    Hi Lee,

    Thanks for reply.
    I have checked with RD. The SAS3 drive does can handle about 24 dB.
    But due to their total loss from SAS3 drive to HDD connector is about 45dB~50dB loss.
    So the worse case is 50dB loss - 24dB =26dB that need a redriver to handle. Therefore, I think DS125BR111 is not suitable for this case.

    I check the spec of DS100BR111 and DS100BR210. Both of them only can support up to 10.3Gbps. Could you help to double confirm if these two solutions can support SAS3 12Gbps and handle 26dB channel loss or not?

    If the customer choose DS100BR111, could you please help to advise the recommended placement?

    Thank you.
    Jim
  • 0 in reply to Jim CHEN
    TI__Mastermind 43795 points
    Hi Jim,

    I would not recommend any redriver for a 45-50dB loss system the risk is extremely high that the system will not work. Remember at 40dB loss the received signal strength is only 1% of the original. With this type of channel attenuation any noise or crosstalk has a very high probability to cause large amounts of jitter on the victim channel.

    Regards,
    Lee