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DS125BR111: Setting for SAS-3 on pin-mode

TerryU
Prodigy 145 points
Part Number: DS125BR111

Hi Experts,

I would use DS125BR111 for SAS-3 interface redriver and am consider setting. Now I have some questions about this device. I use it on pin-mode as ENSMB=0.

1) I set the EQA0/EQB0=1 (LEVEL4),  VODA_DB/VODB_DB=0 and VOD_SEL=1 as recommended setting. In this case, will all ranges of SAS-3 are covered, i.e. there is no problem?  For example, when I put this device with short cable near output and loss is only a few dB, will it work fine?

2) Block diagram shows Equalizer, Pre-driver, Driver. What are the functions of Pre-driver and Driver? Are they only pure amplifiers or do they work for adjusting output to specific level according to SAS-3 format?

Best regards,

Tetsu 

  • 0
    TI__Genius 10946 points

    Hi Tetsu,

    1) Level 4 is expected to have the best performance for SAS-3 applications. If eye performance issues are seen in cases with a small amount of insertion loss, levels 1-3 can be tested to see if over-EQ is the root cause.

    2) From my understanding, the pre-driver stage is a linear amplifier, and the last driver stage sets the output level depending on the device configuration.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    Prodigy 145 points

    Hi Evan,

    Thank  you for  your response.

    1) It depends on eye performance, doesn't it ? I will check it.

    2) Does the last driver adjust the output to the fixed level (Level4) according to VOD_SEL regardless pre-driver output level? It seems that VOD-VID character on Figure.7 in data sheet shows amplifier like character.

    Best regards,

    Tetsu

  • +1 in reply to TerryU
    TI__Genius 10946 points

    Hi Tetsu,

    1) Yes - although we have generally seen the best performance with Level 4 for SAS-3 applications, it is still recommended to try the other levels and compare the eye performance for each.

    2) I believe both stages act as amplifiers, where VOD_SEL will change the driver stage behavior, and VODA_DB will influence the pre-driver stage behavior. The final output voltage will depend on the setting used for both stages.  

    Thank you,

    Evan