SLLS261N July   1997  – April 2021 SN55LVDS31 , SN65LVDS31 , SN65LVDS3487 , SN65LVDS9638

PRODUCTION DATA  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (Continued)
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings (1)
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics: SN55LVDS31
    6. 7.6 Electrical Characteristics: SN65LVDSxxxx
    7. 7.7 Switching Characteristics: SN55LVDS31
    8. 7.8 Switching Characteristics: SN65LVDSxxxx
    9. 7.9 Typical Characteristics
      1. 7.9.1 17
  8. Parameter Measurement Information
    1. 8.1 19
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Driver Disabled Output
      2. 9.3.2 NC Pins
      3. 9.3.3 Unused Enable Pins
      4. 9.3.4 Driver Equivalent Schematics
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Point-to-Point Communications
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Driver Supply Voltage
          2. 10.2.1.2.2 Driver Bypass Capacitance
          3. 10.2.1.2.3 Driver Output Voltage
          4. 10.2.1.2.4 Interconnecting Media
          5. 10.2.1.2.5 PCB Transmission Lines
          6. 10.2.1.2.6 Termination Resistor
          7. 10.2.1.2.7 Driver NC Pins
        3. 10.2.1.3 Application Curve
      2. 10.2.2 Multidrop Communications
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
          1. 10.2.2.2.1 Interconnecting Media
        3. 10.2.2.3 Application Curve
  11. 11Power Supply Recommendations
    1. 11.1 49
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Microstrip vs. Stripline Topologies
      2. 12.1.2 Dielectric Type and Board Construction
      3. 12.1.3 Recommended Stack Layout
      4. 12.1.4 Separation Between Traces
      5. 12.1.5 Crosstalk and Ground Bounce Minimization
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Other LVDS Products
    2. 13.2 Documentation Support
      1. 13.2.1 Related Information
      2. 13.2.2 Receiving Notification of Documentation Updates
      3. 13.2.3 Related Links
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information
Driver Bypass Capacitance

Bypass capacitors play a key role in power distribution circuitry. Specifically, they create low-impedance paths between power and ground. At low frequencies, a good digital power supply offers very-low-impedance paths between its terminals. However, as higher frequency currents propagate through power traces, the source is quite often incapable of maintaining a low-impedance path to ground. Bypass capacitors are used to address this shortcoming. Usually, large bypass capacitors (10 to 1000 μF) at the board-level do a good job up into the kHz range. Due to their size and length of their leads, they tend to have large inductance values at the switching frequencies of modern digital circuitry. To solve this problem, one should resort to the use of smaller capacitors (nF to μF range) installed locally next to the integrated circuit.

Multilayer ceramic chip or surface-mount capacitors (size 0603 or 0805) minimize lead inductances of bypass capacitors in high-speed environments, because their lead inductance is about 1 nH. For comparison purposes, a typical capacitor with leads has a lead inductance around 5 nH.

The value of the bypass capacitors used locally with LVDS chips can be determined by the following formula according to Johnson1, equations 8.18 to 8.21. A conservative rise time of 200 ps and a worst-case change in supply current of 1 A covers the whole range of LVDS devices offered by Texas Instruments. In this example, the maximum power supply noise tolerated is 200 mV; however, this figure varies depending on the noise budget available in your design. (1)

Equation 1. GUID-716D38B7-97AB-4809-8FBE-D416F9CE1FE2-low.gif
Equation 2. GUID-4412874F-7D3B-4AE1-900E-D698271C8BF1-low.gif

The following example lowers lead inductance and covers intermediate frequencies between the board-level capacitor (>10 µF) and the value of capacitance found above (0.001 µF). You should place the smallest value of capacitance as close as possible to the chip.

GUID-05ECF055-0033-4BBD-A550-348CB54FFFC4-low.gifFigure 10-3 Recommended LVDS Bypass Capacitor Layout
Howard Johnson & Martin Graham.1993. High Speed Digital Design – A Handbook of Black Magic. Prentice Hall PRT. ISBN number 013395724.