SBAS572B May   2013  – March 2019 ADS8864

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      No Separate LDO Required for the ADC Supply
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin 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 Timing Requirements: 3-Wire Operation
    7. 7.7 Timing Requirements: 4-Wire Operation
    8. 7.8 Timing Requirements: Daisy-Chain
    9. 7.9 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Equivalent Circuits
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Analog Input
      2. 9.3.2 Reference
      3. 9.3.3 Clock
      4. 9.3.4 ADC Transfer Function
    4. 9.4 Device Functional Modes
      1. 9.4.1 CS Mode
        1. 9.4.1.1 3-Wire CS Mode Without a Busy Indicator
        2. 9.4.1.2 3-Wire CS Mode With a Busy Indicator
        3. 9.4.1.3 4-Wire CS Mode Without a Busy Indicator
        4. 9.4.1.4 4-Wire CS Mode With a Busy Indicator
      2. 9.4.2 Daisy-Chain Mode
        1. 9.4.2.1 Daisy-Chain Mode Without a Busy Indicator
        2. 9.4.2.2 Daisy-Chain Mode With a Busy Indicator
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 ADC Reference Driver
      2. 10.1.2 ADC Input Driver
        1. 10.1.2.1 Input Amplifier Selection
        2. 10.1.2.2 Charge-Kickback Filter
    2. 10.2 Typical Applications
      1. 10.2.1 DAQ Circuit for a 2.5-µs, Full-Scale Step Response
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
      2. 10.2.2 DAQ Circuit for Lowest Distortion and Noise Performance at 400 kSPS
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
      3. 10.2.3 Ultralow-Power DAQ Circuit at 10 kSPS
        1. 10.2.3.1 Design Requirements
        2. 10.2.3.2 Detailed Design Procedure
  11. 11Power Supply Recommendations
    1. 11.1 Power-Supply Decoupling
    2. 11.2 Power Saving
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Community Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

10.2.1.2 Detailed Design Procedure

The application circuit is shown in Figure 63.

In such applications, the primary design requirement is to ensure that the full-scale step input signal settles to 16-bit accuracy at the ADC inputs. This condition is critical to achieve the excellent linearity specifications of the ADC. Therefore, the bandwidth of the charge-kickback RC filter must be large enough to allow optimal settling of the input signal during the ADC acquisition time. The filter capacitor helps reduce the sampling charge injection at the ADC inputs, but degrades the phase margin of the driving amplifier, thereby leading to stability issues. Amplifier stability is maintained by the series isolation resistor.

During the conversion process, binary-weighted capacitors are switched onto the REF pin. In order to support this dynamic load the output of the voltage reference must be buffered with a low-output impedance (high-bandwidth) buffer.

The REF60xx family of voltage references are able to maintain an output voltage within 1 LSB (16-bit) with minimal droop, even during the first conversion while driving the REF pin of the ADS8864. This feature is useful in burst-mode, event-triggered, equivalent-time sampling, and variable-sampling-rate data-acquisition systems.

For the input driving amplifiers, key specifications include rail-to-rail input and output swing, high bandwidth, high slew rate, and fast settling time. The CMOS amplifier meets all these specification requirements for this circuit with a single-supply and low quiescent current. The component values of the antialiasing filter are selected to meet the settling requirements of the system as well as to maintain the stability of the input driving amplifiers.