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

4-Wire CS Mode With a Busy Indicator

This interface option is most useful when a single ADC is connected to an SPI-compatible digital host and an interrupt-driven data transfer is desired. In this interface option, the analog sample is least affected by clock jitter because the CONVST signal (used to sample the input) is independent of the data read operation. In this interface option, DIN is controlled by the digital host and functions as CS (as shown in Figure 56). The pull-up resistor on the DOUT pin ensures that the IRQ pin of the digital host is held high when DOUT goes to 3-state. As shown in Figure 57, when DIN is high, a CONVST rising edge selects CS mode, forces DOUT to 3-state, samples the input signal, and causes the device to enter a conversion phase. In this interface option, CONVST must be held high from the start of the conversion until all data bits are read. Conversion is done with the internal clock and continues regardless of the state of DIN. As a result, DIN (acting as CS) can be pulled low to select other devices on the board. However, DIN must be pulled low before the minimum conversion time (tconv-min) elapses and remains low until the maximum possible conversion time (tconv-max) elapses. A low level on the DIN input at the end of a conversion ensures the device generates a busy indicator.

ADS8864 ai_cs_4wire_conex_busy_bas557.gifFigure 56. Connection Diagram: 4-Wire CS Mode With a Busy Indicator
ADS8864 ai_cs_4wire_tim_busy_bas557.gifFigure 57. Interface Timing Diagram: 4-Wire CS Mode With a Busy Indicator

When conversion is complete, the device enters an acquisition phase and powers down, DOUT comes out of 3-state, and the device outputs a busy indicator bit (low level) on the DOUT pin. This configuration provides a high-to-low transition on the IRQ pin of the digital host. The data bits are clocked out, MSB first, on the 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 17th SCLK falling edge or when DIN goes high, whichever occurs first. Care must be taken so that CONVST and DIN are not both low together at any time during the cycle.