SBAS578A May   2012  – January 2016 ADS4128

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  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
    6. 7.6  Electrical Characteristics: General
    7. 7.7  Digital Characteristics
    8. 7.8  Timing Requirements: LVDS and CMOS Modes
    9. 7.9  Reset Timing Requirements
    10. 7.10 Typical Characteristics
    11. 7.11 Typical Characteristics: Contour
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Migrating From the ADS6149 Family
      2. 8.3.2 Digital Functions and Low-Latency Mode
      3. 8.3.3 Gain for SFDR and SNR Trade-Off
      4. 8.3.4 Offset Correction
      5. 8.3.5 Power Down
        1. 8.3.5.1 Global Power-Down
        2. 8.3.5.2 Standby
        3. 8.3.5.3 Output Buffer Disable
        4. 8.3.5.4 Input Clock Stop
      6. 8.3.6 Power-Supply Sequence
      7. 8.3.7 Output Data Format
    4. 8.4 Device Functional Modes
      1. 8.4.1 Output Interface Modes
        1. 8.4.1.1 Output Interface
        2. 8.4.1.2 DDR LVDS Outputs
        3. 8.4.1.3 LVDS Output Data and Clock Buffers
        4. 8.4.1.4 Parallel CMOS Interface
        5. 8.4.1.5 CMOS Interface Power Dissipation
        6. 8.4.1.6 Input Over-Voltage Indication (OVR Pin)
    5. 8.5 Programming
      1. 8.5.1 Serial Register Readout
      2. 8.5.2 Serial Interface
        1. 8.5.2.1 Register Initialization
    6. 8.6 Register Maps
      1. 8.6.1 Serial Interface Register Map
      2. 8.6.2 Register Description
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Analog Input
      2. 9.1.2 Driving Circuit
        1. 9.1.2.1 Drive Circuit Requirements
      3. 9.1.3 Analog Input
        1. 9.1.3.1 Input Common-Mode
      4. 9.1.4 Clock Input
    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
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
    1. 10.1 Sharing DRVDD and AVDD Supplies
    2. 10.2 Using DC/DC Power Supplies
    3. 10.3 Power Supply Bypassing
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Grounding
      2. 11.1.2 Supply Decoupling
      3. 11.1.3 Exposed Pad
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Device Nomenclature
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

10 Power Supply Recommendations

The ADS4128 has two power supplies, one analog (AVDD) and one digital (DRVDD) supply. Both supplies have a nominal voltage of 1.8 V. The AVDD supply is noise sensitive and the digital supply is not.

10.1 Sharing DRVDD and AVDD Supplies

For best performance, the AVDD supply should be driven by a low-noise linear regulator (LDO) and separated from the DRVDD supply. AVDD and DRVDD can share a single supply, but they should be isolated by a ferrite bead and bypass capacitors, in a PI-filter configuration, at a minimum. The digital noise is concentrated at the sampling frequency and harmonics of the sampling frequency, and could contain noise related to the sampled signal. While developing schematics, leave extra placeholders for additional supply filtering.

10.2 Using DC/DC Power Supplies

DC/DC switching power supplies can be used to power DRVDD without issue. AVDD can be powered from a switching regulator. Noise and spurs on the AVDD power supply affect the SNR and SFDR of the ADC, and appear near DC and as a modulated component around the input frequency. If a switching regulator is used, it should have minimal voltage ripple. Supply filtering should be used to limit the amount of spurious noise at the AVDD supply pins. Extra placeholders should be placed on the schematic for additional filtering. Optimize filtering in the final system to achieve the desired performance. The choice of power supply ultimately depends on the system requirements. For instance, if very low phase noise is required, do not use a switching regulator.

10.3 Power Supply Bypassing

Because the ADS4128 already includes internal decoupling, minimal external decoupling can be used without loss in performance. Decoupling capacitors can help filter external power-supply noise; thus, the optimum number of capacitors depends on the actual application. A 0.1-uF capacitor is recommended near each supply pin. The decoupling capacitors should be placed very close to the converter supply pins.