SBAS905C November   2019  – July 2020 ADS8686S

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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
    6. 6.6  Timing Requirements
    7. 6.7  Switching Characteristics
    8. 6.8  Timing Diagrams: Universal
    9. 6.9  Timing Diagrams: Parallel Data Read
    10. 6.10 Timing Diagrams: Serial Data Read
    11. 6.11 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Analog Inputs
      2. 7.3.2  Analog Input Impedance
      3. 7.3.3  Input Clamp Protection Circuit
      4. 7.3.4  Programmable Gain Amplifier (PGA)
      5. 7.3.5  Second-Order, Programmable, Low-Pass Filter (LPF)
      6. 7.3.6  ADC Driver
      7. 7.3.7  Multiplexer
      8. 7.3.8  Digital Filter and Noise
      9. 7.3.9  Reference
        1. 7.3.9.1 Internal Reference
        2. 7.3.9.2 External Reference
        3. 7.3.9.3 Supplying One VREF to Multiple Devices
      10. 7.3.10 ADC Transfer Function
    4. 7.4 Device Functional Modes
      1. 7.4.1 Device Interface: Pin Description
        1. 7.4.1.1  REFSEL (Input)
        2. 7.4.1.2  RESET (Input)
        3. 7.4.1.3  SEQEN (Input)
        4. 7.4.1.4  HW_RANGESEL[1:0] (Input)
        5. 7.4.1.5  SER/BYTE/PAR (Input)
        6. 7.4.1.6  DB[3:0] (Input/Output)
        7. 7.4.1.7  DB4/SER1W (Input/Output)
        8. 7.4.1.8  DB5/CRCEN (Input/Output)
        9. 7.4.1.9  DB[7:6] (Input/Output)
        10. 7.4.1.10 DB8 (Input/Output)
        11. 7.4.1.11 DB9/BYTESEL (Input/Output)
        12. 7.4.1.12 DB10/SDI (Input/Output)
        13. 7.4.1.13 DB11/SDOB (Input/Output)
        14. 7.4.1.14 DB12/SDOA (Input/Output)
        15. 7.4.1.15 DB13/OS0 (Input/Output)
        16. 7.4.1.16 DB14/OS1 (Input/Output)
        17. 7.4.1.17 DB15/OS2 (Input/Output)
        18. 7.4.1.18 WR/BURST (Input)
        19. 7.4.1.19 SCLK/RD (Input)
        20. 7.4.1.20 CS (Input)
        21. 7.4.1.21 CHSEL[2:0] (Input)
        22. 7.4.1.22 BUSY (Output)
        23. 7.4.1.23 CONVST (Input)
      2. 7.4.2 Device Modes of Operation
        1. 7.4.2.1 Shutdown Mode
        2. 7.4.2.2 Operation Mode
          1. 7.4.2.2.1 Hardware Mode
          2. 7.4.2.2.2 Software Mode
        3. 7.4.2.3 Reset Functionality
        4. 7.4.2.4 Channel Selection
          1. 7.4.2.4.1 Hardware Mode Channel Selection
          2. 7.4.2.4.2 Software Mode Channel Selection
        5. 7.4.2.5 Sequencer
          1. 7.4.2.5.1 Hardware Mode Sequencer
          2. 7.4.2.5.2 Software Mode Sequencer
        6. 7.4.2.6 Burst Sequencer
          1. 7.4.2.6.1 Hardware Mode Burst Sequencer
          2. 7.4.2.6.2 Software Mode Burst Sequencer
        7. 7.4.2.7 Diagnostics
          1. 7.4.2.7.1 Analog Diagnosis
          2. 7.4.2.7.2 Interface Diagnosis: SELF TEST and CRC
    5. 7.5 Programming
      1. 7.5.1 Parallel Interface
        1. 7.5.1.1 Reading Conversion Results
        2. 7.5.1.2 Writing Register Data
        3. 7.5.1.3 Reading Register Data
      2. 7.5.2 Parallel Byte Interface
        1. 7.5.2.1 Reading Conversion Results
        2. 7.5.2.2 Writing Register Data
        3. 7.5.2.3 Reading Register Data
      3. 7.5.3 Serial Interface
        1. 7.5.3.1 Reading Conversion Results
        2. 7.5.3.2 Writing Register Data
        3. 7.5.3.3 Reading Register Data
    6. 7.6 Register Maps
      1. 7.6.1 Page1 Registers
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 8x2 Channel Data Acquisition System (DAQ) for Power Automation
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Input Protection for Electrical Overstress
  9. 9 Power Supply Recommendations
    1. 9.1 Power Supplies
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary

10.1 Layout Guidelines

Figure 10-1 and Figure 10-2 illustrate a printed circuit board (PCB) layout example for the ADS8686S.

  • Keep the analog signal away from the digital lines. This layout keeps the analog input and reference signals away from digital noise.
  • Use a single common ground plane. For designs requiring split analog and digital ground planes, the analog and digital ground planes must be at the same potential joined together in close proximity to the device.
  • Power sources to the ADS8686S must be clean and well-bypassed. As a result of dynamic currents during conversion, each AVDD pin must have a decoupling capacitor to keep the supply voltage stable. Use wide traces or a dedicated analog supply plane to minimize trace inductance and reduce glitches. Use a 10-µF and 0.1-µF ceramic capacitor in close proximity to each analog (AVDD) supply pins (pins 6, 15, 30, and 71) and the digital supply (pin 49).
  • Connect the AVDD supply pins (pins 71 and 30) to bypass capacitors on both the top and bottom layers with an isolated via. Use a separate via to connect the bypass capacitors to the AVDD plane.
  • Decouple the REFCAP pin (pin 31) with a 10-µF, 0805-size capacitor placed in close proximity to the device pin. Avoid placing vias between the REFCAP pin and the decoupling capacitor.
  • Decouple the REGCAP pin (pin 70) with a 10-µF and a 0.1-µF ceramic capacitor placed in close proximity to the device pin. Avoid placing vias between the REGCAP pin and the decoupling capacitor.
  • Decouple the REGCAPD pin (pin 52) with a 10-µF and a 0.1-µF ceramic capacitor placed in close proximity to the device pin. Avoid placing vias between the REGCAPD pin and the decoupling capacitor.
  • If the internal reference of the device is used, decouple the REFIO pin to REFIO_GND with a 10-µF, X7R-grade, 0603-size ceramic capacitor. Place the capacitor on the top layer, close to the device pin. Avoid placing vias between the REFIO pin and the decoupling capacitor.
  • Connect all ground pins (AGND) to the ground plane using short, low-impedance paths and independent vias to the ground plane.