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Original question:

DS25BR110: Can LVDS inputs left floatting in case of connector disconnection ?

DS25BR110: Specification for Vth and Vtl

Shunsuke Nagata
Genius 12590 points
Part Number: DS25BR110

Hi,

My customer has questions for Vth and Vtl. Datasheet show as below:

1. What kinds of condition is cause validation for +/- 100mV? e.g. high temperature condition? High/low voltage condition?

2. Customer confirmed DS25BR110 can detect 4 type of signals. But which signal can device support and which signal cannot device support in attached document?

LVDS_CLK_DATA_signal.pptx

3. If ambient temp is  10~40 degreeC, will the differential input range be small rather than +/-100mV?

4. Is there specific guild line to detect Rin(Input Termination Resistor)?

Regards,
Nagata.

  • 0
    TI__Mastermind 43795 points

    1. The primary reason is under very high or very low input VCM condition.

    2. The LVDS_DATA signals "C" and "D" cannot be supported. 

    2. It is highly likely that LVDS_CLK waveforms "C" and "D" would always be supported.

    3. If the input common mode voltage is at or near 1.2V, yes the input differential range would be small.

    4. We usually just measure it with an ohmmeter.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    TI__Genius 12590 points

    Hi, Lee,

    Thank you very much for your support.

    For 3, User would like to set the differential input range from +/- 100mV to +/-75mV and +/- 50mV. How much common voltage should user set for +/-75mV and +/-50mV?

    For 4, Could you please let me know Recommended max and min value of RIN?

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 43795 points

    Hi Nagata,

    The receiver sensitivity with a common mode input of 1.2V will work well for those signals.

    The minimum and maximum values are approximately 80 - 120 Ohms

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    TI__Genius 12590 points

    Hi, Lee,

    Thank you for your supports. Could you please let me know detail common mode input in below list?

    Currently spec:
    Differential : +/-100mV
    VCM input : 0.05V  ~ VCC-0.05V 

    Additional requirement 1
    Differential : +/-50mV
    VCM input : ??V  ~ ??V 

    Additional requirement 2
    Differential : +/-75mV
    VCM input : ??V  ~ ??V 

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 43795 points

    Hi Nagata,

    The data from device characterization shows better VTH performance.

    Here is the data I located.

      Split      N        Avg     Median      Sigma        Min          Max     -6 Sigma  %FAIL   +6 Sigma

    VTH_N0/ Grouped to: VTH_N0 (mV)
                6456    -2.1676         -2      5.4311        -32           18      -34.754   0.00     30.419   0.00

    The average value is -2.1676mV, the minimum across VCM is -32mV and the maximum is +18mV

    VTH_P0/ Grouped to: VTH_P0 (mV)
                6456   -0.0607  3.2e-11     5.4835        -20           34      -32.962   0.00      32.84    0.02

    The average value is -0.06mV, the minimum across VCM is -20mV and the maximum is +34mV

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    TI__Genius 12590 points

    Hi, Lee,

    Your answer was "1. The primary reason is under very high or very low input VCM condition" for the validation of differential input threshold. Customer would like to know the VCMR for the case of 75mV and 50mV  

    Could you please give me your support to get information which customer need from your data? Because I couldn't find the 75mV and 50mV condition.

    Datasheet shows as below : 

    I would like to know VCMR condition when differential input = 75mV and 50mV instead of 100mV.

    Additional requirement 1
    Differential : +/-50mV
    VCM input : ??V ~  18mV?

    Additional requirement 2
    Differential : +/-75mV
    VCM input :  ??V ~ 34mV? 

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 43795 points

    Hi Nagata,

    Here is a summary of the data which supports the VTH and VTL datasheet specifications.

     

    VT Measurement Values:  - 32mV  to  +34mV  (across the entire Vcm range of 0.05V to VDD-0.05V)

    The data suggests that lower +/- 50mV or +/- 75mV input differential levels are possible, but there is less margin between the worst case measured threshold values and the input signal amplitude.  This will likely cause some AC performance degradation as the input amplitude level approaches the device threshold level.

    Regards,

    Lee