SBAS572B May   2013  – March 2019 ADS8864


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      No Separate LDO Required for the ADC Supply
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  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. Parameter Measurement Information
    1. 8.1 Equivalent Circuits
  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. 3-Wire CS Mode Without a Busy Indicator
        2. 3-Wire CS Mode With a Busy Indicator
        3. 4-Wire CS Mode Without a Busy Indicator
        4. 4-Wire CS Mode With a Busy Indicator
      2. 9.4.2 Daisy-Chain Mode
        1. Daisy-Chain Mode Without a Busy Indicator
        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. Input Amplifier Selection
        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. Design Requirements
        2. Detailed Design Procedure
      2. 10.2.2 DAQ Circuit for Lowest Distortion and Noise Performance at 400 kSPS
        1. Design Requirements
        2. Detailed Design Procedure
      3. 10.2.3 Ultralow-Power DAQ Circuit at 10 kSPS
        1. Design Requirements
        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

3-Wire CS Mode Without a Busy Indicator

This interface option is most useful when a single ADC is connected to an SPI-compatible digital host. In this interface option, DIN can be connected to DVDD and CONVST functions as CS (as shown in Figure 48). As shown in Figure 49, a CONVST rising edge forces DOUT to 3-state, samples the input signal, and causes the device to enter a conversion phase. Conversion is done with the internal clock and continues regardless of the state of CONVST. As a result, CONVST (functioning as CS) can be pulled low after the start of the conversion to select other devices on the board. However, CONVST must return high before the minimum conversion time (tconv-min) elapses and is held high until the maximum possible conversion time (tconv-max) elapses. A high level on CONVST at the end of the conversion ensures the device does not generate a busy indicator.

ADS8864 ai_cs_3wire_conex_bas557.gifFigure 48. Connection Diagram: 3-Wire CS Mode Without a Busy Indicator (DIN = 1)
ADS8864 ai_cs_3wire_tim_bas557.gifFigure 49. Interface Timing Diagram: 3-Wire CS Mode Without a Busy Indicator (DIN = 1)

When conversion is complete, the device enters an acquisition phase and powers down. CONVST (functioning as CS) can be brought low after the maximum conversion time (tconv-max) elapses. On the CONVST falling edge, DOUT comes out of 3-state and the device outputs the MSB of the data. The lower data bits are output on subsequent SCLK falling edges. Data can be read at either SCLK falling or rising edges. Note that with any SCLK frequency, reading data at SCLK falling edge requires the digital host to clock in the data during the th_CK_DO-min time frame. DOUT goes to 3-state after the 16th SCLK falling edge or when CONVST goes high, whichever occurs first.