SNLA475 October   2024 DS250DF410 , DS250DF810 , DS280BR810 , DS280BR820 , DS280DF810 , DS280MB810 , DS560MB410

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Codesign: 25GbE 4-Channel Retimer or Redriver with Crosspoint
    1. 2.1 DS250DF410 Retimer Overview
    2. 2.2 DS560MB410 Redriver Overview
    3. 2.3 Pin Comparison Table
    4. 2.4 Codesign Schematic Example
    5. 2.5 Notable Codesign Elements
      1. 2.5.1 Calibration Clock
      2. 2.5.2 SMBus Address
      3. 2.5.3 SMBus Controller Mode
      4. 2.5.4 SMBus Pull-Up Resistors
      5. 2.5.5 Interrupt Output
      6. 2.5.6 Mux Select Inputs
  6. 3Codesign: 25GbE 8-Channel Retimer or Redriver with Crosspoint
    1. 3.1 DS250DF810 and DS280DF810 Retimers Overview
    2. 3.2 DS280BR810, DS280BR820, and DS280MB810 Redrivers Overview
    3. 3.3 Pin Comparison Table
    4. 3.4 Codesign Schematic Example
    5. 3.5 Notable Codesign Elements
      1. 3.5.1 AC Coupling
      2. 3.5.2 Calibration Clock
      3. 3.5.3 SMBus Address
      4. 3.5.4 SMBus Controller Mode
      5. 3.5.5 SMBus Pull-Up Resistors
      6. 3.5.6 Interrupt Output
      7. 3.5.7 Mux Select Inputs
  7. 4Summary
  8. 5References

3.5.5 SMBus Pull-Up Resistors

The SMBus interface uses open-drain clock and data inputs/outputs to enable device communication. The SDA and SDC lines each require a single 2kΩ to 5kΩ pull-up resistor. This codesign example offers multiple pull-up options.

  • R21 and R22 are populated by default. These are 4.7kΩ pull-ups to 3.3V supply.
  • R19 and R20 can be populated to use 2.7kΩ pull-ups to 2.5V supply near the retimer or redriver. These can be useful for debug purposes if the device SDA/SDC pins need to be disconnected from the main SMBus interface (by depopulating R23 and R24).
  • R29 and R30 can be populated to use 2.7kΩ pull-ups to 2.5V supply near the external EEPROM. These can be useful for debug purposes if the EEPROM SDA/SDC pins need to be disconnected from the main SMBus interface (by depopulating R31 and R32).