SBAS533E March   2011  – February 2023 ADS4222 , ADS4225 , ADS4226 , ADS4242 , ADS4245 , ADS4246

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions – LVDS Mode
    2.     Pin Functions – CMOS Mode
  7. 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: ADS4246, ADS4245, ADS4242
    6. 7.6  Electrical Characteristics: ADS4226, ADS4225, ADS4222
    7. 7.7  Electrical Characteristics: General
    8. 7.8  Digital Characteristics
    9. 7.9  Timing Requirements: LVDS and CMOS Modes (1)
    10. 7.10 Serial Interface Timing Characteristics (1)
    11. 7.11 Reset Timing (Only When Serial Interface Is Used)
    12. 7.12 Typical Characteristics
      1. 7.12.1 ADS4246
      2. 7.12.2 ADS4245
      3. 7.12.3 ADS4242
      4. 7.12.4 ADS4226
      5. 7.12.5 ADS4225
      6. 7.12.6 ADS4222
      7. 7.12.7 General
      8. 7.12.8 Contour
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Feature Description
      1. 8.3.1 Analog Input
        1. 8.3.1.1 Drive Circuit Requirements
        2. 8.3.1.2 Driving Circuit
      2. 8.3.2 Clock Input
      3. 8.3.3 Digital Functions
      4. 8.3.4 Gain for SFDR/SNR Trade-off
      5. 8.3.5 Offset Correction
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-Down
        1. 8.4.1.1 Global Power-Down
        2. 8.4.1.2 Channel Standby
        3. 8.4.1.3 Input Clock Stop
    5. 8.5 Programming
      1. 8.5.1 47
      2. 8.5.2 Parallel Configuration Only
      3. 8.5.3 Serial Interface Configuration Only
      4. 8.5.4 Using Both Serial Interface and Parallel Controls
      5. 8.5.5 Parallel Configuration Details
      6. 8.5.6 Serial Interface Details
        1. 8.5.6.1 Register Initialization
        2. 8.5.6.2 Serial Register Readout
      7. 8.5.7 Digital Output Information
        1. 8.5.7.1 Output Interface
        2. 8.5.7.2 DDR LVDS Outputs
        3. 8.5.7.3 LVDS Buffer
        4. 8.5.7.4 Parallel CMOS Interface
        5. 8.5.7.5 CMOS Interface Power Dissipation
        6. 8.5.7.6 Multiplexed Mode of Operation
        7. 8.5.7.7 Output Data Format
    6. 8.6 Register Maps
      1. 8.6.1 64
      2. 8.6.2 Description Of Serial Registers
  9. 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
        1. 9.2.2.1 Analog Input
        2. 9.2.2.2 Clock Driver
        3. 9.2.2.3 Digital Interface
        4. 9.2.2.4 SNR and Clock Jitter
      3. 9.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
      1. 9.3.1 Sharing DRVDD and AVDD Supplies
      2. 9.3.2 Using DC/DC Power Supplies
      3. 9.3.3 Power Supply Bypassing
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
        1. 9.4.1.1 Grounding
        2. 9.4.1.2 Supply Decoupling
        3. 9.4.1.3 Exposed Pad
        4. 9.4.1.4 Routing Analog Inputs
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Device Nomenclature
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

8.5.7.3 LVDS Buffer

The equivalent circuit of each LVDS output buffer is shown in #SBAS509IMG5887. After reset, the buffer presents an output impedance of 100 Ω to match with the external 100-Ω termination.

GUID-18F884C7-A94F-4A2E-9673-1594A1950265-low.gif
Default swing across 100-Ω load is ±350 mV. Use the LVDS SWING bits to change the swing.
Figure 8-22 LVDS Buffer Equivalent Circuit

The VDIFF voltage is nominally 350 mV, resulting in an output swing of ±350 mV with 100-Ω external termination. The VDIFF voltage is programmable using the LVDS SWING register bits from ±125 mV to ±570 mV.

Additionally, a mode exists to double the strength of the LVDS buffer to support 50-Ω differential termination, as shown in #SBAS533IMG5238. This mode can be used when the output LVDS signal is routed to two separate receiver chips, each using a 100-Ω termination. The mode can be enabled using the LVDS DATA STRENGTH and LVDS CLKOUT STRENGTH register bits for data and output clock buffers, respectively.

The buffer output impedance behaves in the same way as a source-side series termination. By absorbing reflections from the receiver end, it helps to improve signal integrity.

GUID-D2BCA6EC-943A-4375-905D-CF29A181FB27-low.gifFigure 8-23 LVDS Buffer Differential Termination