SBAS456B December   2008  – January 2016 ADS7828-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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 for ADS7828E
    6. 6.6  Electrical Characteristics for ADS7828EB
    7. 6.7  Electrical Characteristics for ADS7828E
    8. 6.8  Electrical Characteristics for ADS7828EB
    9. 6.9  Switching Characteristics
    10. 6.10 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Analog Input
      2. 7.3.2 Reference
      3. 7.3.3 Digital Interface
    4. 7.4 Device Functional Modes
      1. 7.4.1 Address Byte
      2. 7.4.2 Command Byte
      3. 7.4.3 Initiating Conversion
      4. 7.4.4 Reading Data
      5. 7.4.5 Reading in Fast or Standard (F/S) Mode
      6. 7.4.6 Reading in High-Speed (HS) Mode
      7. 7.4.7 Reading With Reference On or Off
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Basic Connections
        1. 8.1.1.1 Connecting Multiple Devices
        2. 8.1.1.2 Using GPIO Ports for Communication
        3. 8.1.1.3 Single-Ended Inputs
    2. 8.2 Typical Applications
      1. 8.2.1 ADS7828-Q1 With Current Shunt Monitor
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Part Selection
          2. 8.2.1.2.2 Full-Scale Differential Range
          3. 8.2.1.2.3 Circuit Implementation
        3. 8.2.1.3 Application Curve
  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

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10 Layout

10.1 Layout Guidelines

For optimum performance, care should be taken with the physical layout of the ADS7828 circuitry. The basic SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground connections, and digital inputs that occur just prior to latching the output of the analog comparator. Therefore, during any single conversion for an "n-bit" SAR converter, there are n "windows" in which large external transient voltages can easily affect the conversion result. Such glitches might originate from switching power supplies, nearby digital logic, and high-power devices.

With this in mind, power to the ADS7828 should be clean and well-bypassed. A 0.1-μF ceramic bypass capacitor should be placed as close to the device as possible. A 1-μF to 10-μF capacitor may also be needed if the impedance of the connection between +VDD and the power supply is high.

The ADS7828 architecture offers no inherent rejection of noise or voltage variation in regards to using an external reference input. This is of particular concern when the reference input is tied to the power supply. Any noise and ripple from the supply will appear directly in the digital results. While high-frequency noise can be filtered out, voltage variation due to line frequency (50 Hz or 60 Hz) can be difficult to remove.

The GND pin should be connected to a clean ground point. In many cases, this will be the "analog" ground. Avoid connections that are too near the grounding point of a microcontroller or digital signal processor. The ideal layout will include an analog ground plane dedicated to the converter and associated analog circuitry.

10.2 Layout Example

ADS7828-Q1 ADS7828-Q1_LayoutEx.gif Figure 27. Layout Example