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LMH1297: Questions for register setting

Kazuki Kuramochi
Genius 10505 points
Part Number: LMH1297

Hello Expert,

I have questions regarding LMH1297's register setting.
Would you answer following questions?

  1. Would you tell me how to select HOST_EQ0 setting when we use awkward length cable?
    1. The datasheet only specified this value for the case of "<1inch"/"1-2inches"/"4-5inches"/"8-10inches".
    2. Therefore we'd like to know about how to select this setting when they use awkward length cable as like as 3inches.
  2. Are configurable settings of OUT0 Output control[0x30]'s  tx0_vod[2:0] only "000", "010", "100", "110"?
  3. Are configurable settings of OUT0 De-emphasis control[0x31]'s  tx0_dem[2:0] only "000", "010", "111"?
    1. For 2. and 3. Programable guide only indicate those value on chart. Does it mean there isn't other intermediate setting as like as "011"?

I'm looking forward to hearing back from you.

Thank you and best regards,
Kazuki Kuramochi

  • 0
    TI__Guru* 93670 points

    Greetings,

    1). Through the register settings, you can control or set different manual CTLE settings. It is recommended to use float on this pin. This allows the device to automatically select appropriate CTLE settings.

    2). Yes there are three bits to control OUT0 output amplitude. Reg 0x30[2:0] provide 8 different settings.

    3). Same as #2, reg 0x31[2:0] three bits control output de-emphasis settings.

    Correct for items 2 & 3 there is not intermediate values.

    Regards,Nasser

  • 0 in reply to Nasser Mohammadi
    TI__Genius 10505 points

    Hello Nasser,

    Thank you for your swift reply.
    I have your answer for question 1.

    As far as I confirm, in CD mode. HOST-EQ0 give the automatically "CTLE" setting but output driver setting is just applied default(570mVpp/-0.4dB).
    Also, in EQ mode, output driver setting is just following HOST_EQ0 condition.
    So LMH1297's output driver setting won't be appropriate setting automatically and they need to chose appropriate OUT0's VOD and DEM setting.
    Is this understanding correct?

    Also if they need to apply appropriate setting for OUT0 VOD and DEM, would you tell me about which setting they should apply during intermediate board trace condition as like as 3iches?
    For example, They should use HOST_EQ as F/R or they should change VOD individually though i2c or etc...


    Best regards,
    Kazuki Kuramochi

  • +1 in reply to Kazuki Kuramochi
    TI__Guru* 93670 points

    Greetings,

    1). Your understanding is correct.

    2). Suggestion is to start with minimum VOD and no DE setting. Let FPGA or receiver do the equalization. If needed VOD can be increased one step at a time and then DE.

    Regards,,Nasser

  • 0 in reply to Nasser Mohammadi
    TI__Genius 10505 points

    Hello Nasser-san,

    Thank you for your swift reply.
    I understand.

    Thank you and best regards,
    Kazuki Kuramochi