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DS125BR401A: Some question for channel loss...

Peter Tseng
Genius 5810 points
Part Number: DS125BR401A

Dear Sirs,

I have a question about the channel loss!

As below chart, if the DS125BR401A have -24dB ability and the SAS-3 controller has -24dB ability, too.

May I think the total channel loss is -48dB for BR401A and controller 1 and -34dB for controller 0 and BR401A?

Thanks.

  • 0
    TI__Mastermind 19225 points

    Hi,

    Per datasheet the DS125BR401A compensation capability is as follows:

    • Receive CTLE up to 24 dB at 6 GHz
    • Transmit de-emphasis up to 10dB

    However, insertion loss is not the only signal impairment limiting your link reach. Parameters such as reflections, crosstalk and SAS-3 controller chip output jitter will also affect your reach. I would recommend to perform system simulation with TI redriver IBIS-AMI model plus your own channel models to assess signal integrity for your design. As an initial guidance I would recommend to target a DS125BR401A  max input channel loss of around 20dB. If your system simulations show good margin, then you might allocate input loss closer to 24dB for this channel.

    Thanks,

    Rodrigo Natal

    HSSC Applications Engineer

  • 0 in reply to Rodrigo Natal
    Genius 5810 points

    Hi Sir,

    Here are others questions from customer, please help.

    Thanks.

    1. As datasheet, the EQ ability can up to 31dB@6GHz, why only mark 24dB, not 31dB?

    2. Since SAS3 has 24dB loss compensation ability, may I use -24dB for it instead of -10dB? 

     

    3. About the dB value in the datasheet, do they come with 20log(Vo/Vin) formula?

  • 0 in reply to Peter Tseng
    TI__Mastermind 19225 points

    Hi,

    1. As datasheet, the EQ ability can up to 31dB@6GHz, why only mark 24dB, not 31dB?
      • My mistake, you are correct
    2. Since SAS3 has 24dB loss compensation ability, may I use -24dB for it instead of -10dB? 
      • Yes, that would be my suggestion. It's more efficient to rely on the Rx to provide EQ, then use Tx EQ to fine tune as needed
    3. About the dB value in the datasheet, do they come with 20log(Vo/Vin) formula?
      • This equation is correct.
      • If you have dB value and one of the voltage parameter values you can then calculate the missing one

    Thanks,

    Rodrigo Natal

  • 0 in reply to Rodrigo Natal
    Genius 5810 points

    Hi Sir,

    May I ask one more question?

    May I use 1pcs EEPROM to configure 2pcs BR401A on the same board while power on?

    If yes, does anything needs to pay attention to?

    Thanks.

  • 0 in reply to Peter Tseng
    TI__Mastermind 19225 points

    Yes, you may use a single EEPROM to program multiple devices. The key thing to pay attention to is the configuration of the EN_SMB, READ_EN_N and ALL_DONE_N control pins as well as SDA/SCL. Refer to the datasheet for details.

    Thanks,

    Rodrigo