SBAS815A February   2017  – June 2017 ADS114S06 , ADS114S08

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Functional Block Diagram
  4. 4 Revision History
  5. 5 Device Family 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 Characteristics
    7. 7.7 Switching Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Noise Performance
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Multiplexer
      2. 9.3.2  Low-Noise Programmable Gain Amplifier
        1. 9.3.2.1 PGA Input-Voltage Requirements
        2. 9.3.2.2 PGA Rail Flags
        3. 9.3.2.3 Bypassing the PGA
      3. 9.3.3  Voltage Reference
        1. 9.3.3.1 Internal Reference
        2. 9.3.3.2 External Reference
        3. 9.3.3.3 Reference Buffers
      4. 9.3.4  Clock Source
      5. 9.3.5  Delta-Sigma Modulator
      6. 9.3.6  Digital Filter
        1. 9.3.6.1 Low-Latency Filter
          1. 9.3.6.1.1 Low-Latency Filter Frequency Response
          2. 9.3.6.1.2 Data Conversion Time for the Low-Latency Filter
        2. 9.3.6.2 Sinc3 Filter
          1. 9.3.6.2.1 Sinc3 Filter Frequency Response
          2. 9.3.6.2.2 Data Conversion Time for the Sinc3 Filter
        3. 9.3.6.3 Note on Conversion Time
        4. 9.3.6.4 50-Hz and 60-Hz Line Cycle Rejection
        5. 9.3.6.5 Global Chop Mode
      7. 9.3.7  Excitation Current Sources (IDACs)
      8. 9.3.8  Bias Voltage Generation
      9. 9.3.9  System Monitor
        1. 9.3.9.1 Internal Temperature Sensor
        2. 9.3.9.2 Power Supply Monitors
        3. 9.3.9.3 Burn-Out Current Sources
      10. 9.3.10 Status Register
        1. 9.3.10.1 POR Flag
        2. 9.3.10.2 RDY Flag
        3. 9.3.10.3 PGA Output Voltage Rail Monitors
        4. 9.3.10.4 Reference Monitor
      11. 9.3.11 General-Purpose Inputs and Outputs (GPIOs)
      12. 9.3.12 Low-Side Power Switch
      13. 9.3.13 Cyclic Redundancy Check (CRC)
      14. 9.3.14 Calibration
        1. 9.3.14.1 Offset Calibration
        2. 9.3.14.2 Gain Calibration
    4. 9.4 Device Functional Modes
      1. 9.4.1 Reset
        1. 9.4.1.1 Power-On Reset
        2. 9.4.1.2 RESET Pin
        3. 9.4.1.3 Reset by Command
      2. 9.4.2 Power-Down Mode
      3. 9.4.3 Standby Mode
      4. 9.4.4 Conversion Modes
        1. 9.4.4.1 Continuous Conversion Mode
        2. 9.4.4.2 Single-Shot Conversion Mode
        3. 9.4.4.3 Programmable Conversion Delay
    5. 9.5 Programming
      1. 9.5.1 Serial Interface
        1. 9.5.1.1 Chip Select (CS)
        2. 9.5.1.2 Serial Clock (SCLK)
        3. 9.5.1.3 Serial Data Input (DIN)
        4. 9.5.1.4 Serial Data Output and Data Ready (DOUT/DRDY)
        5. 9.5.1.5 Data Ready (DRDY)
        6. 9.5.1.6 Timeout
      2. 9.5.2 Data Format
      3. 9.5.3 Commands
        1. 9.5.3.1  NOP
        2. 9.5.3.2  WAKEUP
        3. 9.5.3.3  POWERDOWN
        4. 9.5.3.4  RESET
        5. 9.5.3.5  START
        6. 9.5.3.6  STOP
        7. 9.5.3.7  SYOCAL
        8. 9.5.3.8  SYGCAL
        9. 9.5.3.9  SFOCAL
        10. 9.5.3.10 RDATA
        11. 9.5.3.11 RREG
        12. 9.5.3.12 WREG
      4. 9.5.4 Reading Data
        1. 9.5.4.1 Read Data Direct
        2. 9.5.4.2 Read Data by RDATA Command
        3. 9.5.4.3 Sending Commands When Reading Data
      5. 9.5.5 Interfacing with Multiple Devices
    6. 9.6 Register Map
      1. 9.6.1 Configuration Registers
        1. 9.6.1.1  Device ID Register (address = 00h) [reset = xxh]
          1. Table 26. Device ID (ID) Register Field Descriptions
        2. 9.6.1.2  Device Status Register (address = 01h) [reset = 80h]
          1. Table 27. Device Status (STATUS) Register Field Descriptions
        3. 9.6.1.3  Input Multiplexer Register (address = 02h) [reset = 01h]
          1. Table 28. Input Multiplexer (INPMUX) Register Field Descriptions
        4. 9.6.1.4  Gain Setting Register (address = 03h) [reset = 00h]
          1. Table 29. Gain Setting (PGA) Register Field Descriptions
        5. 9.6.1.5  Data Rate Register (address = 04h) [reset = 14h]
          1. Table 30. Data Rate (DATARATE) Register Field Descriptions
        6. 9.6.1.6  Reference Control Register (address = 05h) [reset = 10h]
          1. Table 31. Reference Control (REF) Register Field Descriptions
        7. 9.6.1.7  Excitation Current Register 1 (address = 06h) [reset = 00h]
          1. Table 32. Excitation Current Register 1 (IDACMAG) Register Field Descriptions
        8. 9.6.1.8  Excitation Current Register 2 (address = 07h) [reset = FFh]
          1. Table 33. Excitation Current Register 2 (IDACMUX) Register Field Descriptions
        9. 9.6.1.9  Sensor Biasing Register (address = 08h) [reset = 00h]
          1. Table 34. Sensor Biasing (VBIAS) Register Field Descriptions
        10. 9.6.1.10 System Control Register (address = 09h) [reset = 10h]
          1. Table 35. System Control (SYS) Register Field Descriptions
        11. 9.6.1.11 Reserved Register (address = 0Ah) [reset = 00h]
          1. Table 36. Reserved Register Field Descriptions
        12. 9.6.1.12 Offset Calibration Register 1 (address = 0Bh) [reset = 00h]
          1. Table 37. Offset Calibration Register 1 (OFCAL0) Register Field Descriptions
        13. 9.6.1.13 Offset Calibration Register 2 (address = 0Ch) [reset = 00h]
          1. Table 38. Offset Calibration Register 2 (OFCAL1) Register Field Descriptions
        14. 9.6.1.14 Reserved Register (address = 0Dh) [reset = 00h]
          1. Table 39. Reserved Register Field Descriptions
        15. 9.6.1.15 Gain Calibration Register 1 (address = 0Eh) [reset = 00h]
          1. Table 40. Gain Calibration Register 1 (FSCAL0) Field Descriptions
        16. 9.6.1.16 Gain Calibration Register 2 (address = 0Fh) [reset = 40h]
          1. Table 41. Gain Calibration Register 2 (FSCAL1) Field Descriptions
        17. 9.6.1.17 GPIO Data Register (address = 10h) [reset = 00h]
          1. Table 42. GPIO Data (GPIODAT) Register Field Descriptions
        18. 9.6.1.18 GPIO Configuration Register (address = 11h) [reset = 00h]
          1. Table 43. GPIO Configuration (GPIOCON) Register Field Descriptions
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Serial Interface Connections
      2. 10.1.2 Analog Input Filtering
      3. 10.1.3 External Reference and Ratiometric Measurements
      4. 10.1.4 Establishing a Proper Input Voltage
      5. 10.1.5 Unused Inputs and Outputs
      6. 10.1.6 Pseudo Code Example
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Register Settings
      3. 10.2.3 Application Curves
    3. 10.3 Do's and Don'ts
  11. 11Power Supply Recommendations
    1. 11.1 Power Supplies
    2. 11.2 Power-Supply Sequencing
    3. 11.3 Power-On Reset
    4. 11.4 Power-Supply Decoupling
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Development Support
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Related Links
    4. 13.4 Receiving Notification of Documentation Updates
    5. 13.5 Community Resources
    6. 13.6 Trademarks
    7. 13.7 Electrostatic Discharge Caution
    8. 13.8 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10.1.2 Analog Input Filtering

Analog input filtering serves two purposes: first, to limit the effect of aliasing during the sampling process and second, to reduce external noise from being a part of the measurement.

As with any sampled system, aliasing can occur if proper antialias filtering is not in place. Aliasing occurs when frequency components are present in the input signal that are higher than half the sampling frequency of the ADC (also known as the Nyquist frequency). These frequency components are folded back and show up in the actual frequency band of interest below half the sampling frequency. Note that inside a ΔΣ ADC, the input signal is oversampled at the modulator frequency, fMOD and not at the output data rate. The filter response of the digital filter repeats at multiples of fMOD, as shown in Figure 112. Signals or noise up to a frequency where the filter response repeats are attenuated to a certain amount by the digital filter depending on the filter architecture. Any frequency components present in the input signal around the modulator frequency or multiples thereof are not attenuated and alias back into the band of interest, unless attenuated by an external analog filter.

ADS114S06 ADS114S08 AliasingEffect_bas501.gifFigure 112. Effect of Aliasing

Many sensor signals are inherently band limited; for example, the output of a thermocouple has a limited rate of change. In this case, the sensor signal does not alias back into the pass band when using a ΔΣ ADC. However, any noise pick-up along the sensor wiring or the application circuitry can potentially alias into the pass band. Power line-cycle frequency and harmonics are one common noise source. External noise can also be generated from electromagnetic interference (EMI) or radio frequency interference (RFI) sources, such as nearby motors and cellular phones. Another noise source typically exists on the printed circuit board (PCB) itself in the form of clocks and other digital signals. Analog input filtering helps remove unwanted signals from affecting the measurement result.

A first-order resistor-capacitor (RC) filter is (in most cases) sufficient to either eliminate aliasing, or to reduce the effect of aliasing to a level below the noise floor of the sensor. Ideally, any signal beyond fMOD / 2 is attenuated to a level below the noise floor of the ADC. The digital filter of the ADS114S0x attenuates signals to a certain degree, as illustrated in the filter response plots in the Digital Filter section. In addition, noise components are usually smaller in magnitude than the actual sensor signal. Therefore, using a first-order RC filter with a cutoff frequency set at the output data rate or 10 times higher is generally a good starting point for a system design.

Internal to the device, prior to the PGA inputs, is an EMI filter; see Figure 50. The cutoff frequency of this filter is approximately 40 MHz and helps reject high-frequency interference.