SNLS450A January   2014  – June 2015 DS125DF111

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration And Functions
  6. 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 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Device Data Path Operation
        1. 7.3.1.1 Input Channel Equalization
        2. 7.3.1.2 Clock and Data Recovery
        3. 7.3.1.3 PRBS Pattern Generator
        4. 7.3.1.4 Datapath Multiplexer and Output Driver
        5. 7.3.1.5 Reference Clock
        6. 7.3.1.6 Control Pins
          1. 7.3.1.6.1 Pin Mode Limitation
        7. 7.3.1.7 Eye Opening Monitor
    4. 7.4 Device Functional Modes
      1. 7.4.1 Control Pin Mode
      2. 7.4.2 SMBus Master Mode and SMBus Slave Mode
    5. 7.5 Programming
      1. 7.5.1 SMBus Interface
        1. 7.5.1.1  Address Lines
        2. 7.5.1.2  Device Configuration in SMBus Slave Mode
        3. 7.5.1.3  Bit Fields in the Register Set
        4. 7.5.1.4  Writing To and Reading from the Control/Shared Registers
        5. 7.5.1.5  SMBus Strap Observation
        6. 7.5.1.6  Interrupt Channel Flag Bits
        7. 7.5.1.7  Control/Shared Register Reset
        8. 7.5.1.8  Device Revision and Device ID
        9. 7.5.1.9  Channel Select Register
        10. 7.5.1.10 Resetting Individual Channels of the Retimer
        11. 7.5.1.11 Rate and Subrate Setting
        12. 7.5.1.12 Overriding the CTLE Boost Setting
        13. 7.5.1.13 Overriding the Output Multiplexer
        14. 7.5.1.14 Overriding the VCO Divider Selection
        15. 7.5.1.15 Using the Internal Eye Opening Monitor
        16. 7.5.1.16 Overriding the DFE Tap Weights and Polarities
        17. 7.5.1.17 Enabling Slow Rise/Fall Time on the Output Driver
        18. 7.5.1.18 Using the PRBS Generator
        19. 7.5.1.19 Inverting the Output Polarity
        20. 7.5.1.20 Figure of Merit Adaption
        21. 7.5.1.21 Setting the Rate and Subrate for Lock Acquisition
        22. 7.5.1.22 Setting the Adaption/Lock Mode
        23. 7.5.1.23 Initiating Adaption
        24. 7.5.1.24 Overriding the CTLE Settings Used for CTLE Adaption
        25. 7.5.1.25 Setting the Output Differential Voltage
        26. 7.5.1.26 Setting the Output De-Emphasis Setting
        27. 7.5.1.27 CTLE Setting for Divide by 4 and Divide by 8 VCO Ranges
    6. 7.6 Register Maps
      1. 7.6.1 Reading To and Writing from the Channel Registers
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
        1. 8.2.3.1 SFF-8431 Testing
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The DS125DF111 is a 2 channel retimer that support many different data rates and application spaces.

8.2 Typical Application

Figure 9 shows a typical implementation for the DS125DF111 in a back plane application. The DS125DF111 can also be used for front port applications. The DS125DF111 supports data rates for CPRI, Infiniband, Ethernet, Interlaken and other custom data rates.

DS125DF111 switch_fabric_line_card.gifFigure 9. Typical Application

8.2.1 Design Requirements

This section lists some critical areas for high speed printed circuit board design consideration and study.

  • Utilize 100-Ω differential impedance traces.
  • Back-drill connector vias and signal vias to minimize stub length.
  • Use reference plane vias to ensure a low inductance path for the return current.
  • Place AC-Coupling capacitors for the transmitter links near the receiver for that channel.
  • The maximum body size for AC-coupling capacitors is 0402.

8.2.2 Detailed Design Procedure

To begin the design process determine the following:

  • Select a reference clock frequency and routing scheme.
  • Plan out channel connectivity. Be sure to note any desired polarity inversion routing in the board schematics.
  • Ensure that each device has a unique SMBus address if the control bus is shared with other devices or components.
  • Use the IBIS-AMI model for simple channel simulations before PCB layout is complete.

Initialization Sequence: Channel Register Configurations repeated for all desired channels:

  • CDR reset
  • Adapt Mode Configuration
  • Data rate selection
  • Output driver VOD and De-Emphasis Optional Interrupt enable
  • Optional Reference clock loop through enable
  • CDR reset release

8.2.3 Application Curves

8.2.3.1 SFF-8431 Testing

Testing for Receiver Jitter Tolerance based on SFF-8431 section D11.

  • Datarate: 10.3125 Gbps
  • PRBS15 Pattern
  • Output Amplitude: 700 mV
  • Periodic Jitter: 70 mUI at 20 MHz
  • ISI Jitter: 10" 4-mil FR4 differential microstrip + Limiting Amplifier
  • Random Jitter noise source: Agilent 346B

The SFF-8431 specification combines deterministic, random, and periodic jitter components. The combination of these jitter components has been measured and calibrated to ensure adequate levels of individual jitter components and total jitter.

DS125DF111 sffinput.gifFigure 10. SFF-8431 Rx Input Jitter Profile
DS125DF111 eye.pngFigure 11. SFF-8431 Output Jitter Eye Mask

The SFF-8431 specification defines a transmit eye mask to ensure robust signal reception across the host - module interface.