SNAS828A february   2022  – june 2023 LMK1D1208I

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Device Comparison
  7. 6 Pin Configuration and Functions
  8. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  9. 8 Parameter Measurement Information
  10. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Fail-Safe Input
      2. 9.3.2 Input Stage Configurability
      3. 9.3.3 Dual Output Bank
      4. 9.3.4 I2C
        1. 9.3.4.1 I2C Address Assignment
      5. 9.3.5 LVDS Output Termination
      6. 9.3.6 Input Termination
    4. 9.4 Device Functional Modes
      1. 9.4.1 Input Enable Control
      2. 9.4.2 Bank Input Selection
      3. 9.4.3 Bank Mute Control
      4. 9.4.4 Output Enable Control
      5. 9.4.5 Output Amplitude Selection
    5. 9.5 Programming
    6. 9.6 Register Maps
      1. 9.6.1 LMK1D1208I Registers
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
      3. 10.2.3 Application Curves
    3. 10.3 Power Supply Recommendations
    4. 10.4 Layout
      1. 10.4.1 Layout Guidelines
      2. 10.4.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  13. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Package Option Addendum
    2. 12.2 Tape and Reel Information

10.2.1 Design Requirements

The LMK1D1208I shown in Figure 10-1 is configured to select two inputs: a 156.25-MHz LVDS clock from the backplane at IN0, or a secondary 156.25-MHz LVCMOS 2.5-V oscillator at IN1. 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. 0.1-µF capacitors are used to reduce noise on both VAC_REF and IN1_N. Either input signal can be then fanned out to desired devices via register control. The configuration example is driving four 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 LMK1D1208I. 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 LMK1D1208I. Again, no additional components are required.
  • The FPGA requires external AC coupling, but has internal termination. 0.1-µF capacitors are placed to provide AC coupling. Similarly, the CPU is internally terminated, and requires only external AC-coupling capacitors.
  • The unused outputs of the LMK1D1208I can be disabled by clearing the corresponding OUTx_EN register through I2C. This results in a lower power consumption.