SNAS815C December   2020  – February 2026 LMK1D1204 , LMK1D1208

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
    1. 4.1 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Fail-Safe Input and Hysteresis
      2. 8.3.2 Input Mux
    4. 8.4 Device Functional Modes
      1. 8.4.1 LVDS Output Termination
      2. 8.4.2 Input Termination
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

9.2.1 Design Requirements

The LMK1D120x shown in Figure 9-1 is configured to select two inputs: a 156.25MHz LVDS clock from the backplane, or a secondary 156.25MHz LVCMOS 2.5V oscillator. The LVDS clock is AC-coupled and biased using the integrated reference voltage generator. A resistor divider is used to set the threshold voltage correctly for the LVCMOS clock. 0.1µF capacitors are used to reduce noise on both VAC_REF and SECREF_N. Either input signal can be then fanned out to desired devices, as shown. The configuration example is driving 4 LVDS receivers in a line card application with the following properties:

  • The PHY device is capable of DC-coupling with an LVDS driver such as the LMK1D120x. This PHY device features internal termination so no additional components are required for proper operation.
  • The ASIC LVDS receiver features internal termination and operates at the same common-mode voltage as the LMK1D120x. Again, no additional components are required.
  • The FPGA requires external AC-coupling, but has internal termination. 0.1µF capacitors are placed to provide AC-coupling. Similarly, the CPU is internally terminated, and requires only external AC-coupling capacitors.
  • Unused outputs of the LMK1D device are terminated differentially with a 100Ω resistor for optimum performance.