SBAS444E May   2009  – December 2024 ADS1113 , ADS1114 , ADS1115

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5.   Device Comparison Table
  6. 4 Pin Configuration and Functions
  7. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements: I2C
    7. 5.7 Typical Characteristics
  8. 6 Parameter Measurement Information
    1. 6.1 Noise Performance
  9. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Multiplexer
      2. 7.3.2 Analog Inputs
      3. 7.3.3 Full-Scale Range (FSR) and LSB Size
      4. 7.3.4 Voltage Reference
      5. 7.3.5 Oscillator
      6. 7.3.6 Output Data Rate and Conversion Time
      7. 7.3.7 Digital Comparator (ADS1114 and ADS1115 Only)
      8. 7.3.8 Conversion Ready Pin (ADS1114 and ADS1115 Only)
      9. 7.3.9 SMbus Alert Response
    4. 7.4 Device Functional Modes
      1. 7.4.1 Reset and Power-Up
      2. 7.4.2 Operating Modes
        1. 7.4.2.1 Single-Shot Mode
        2. 7.4.2.2 Continuous-Conversion Mode
      3. 7.4.3 Duty Cycling For Low Power
    5. 7.5 Programming
      1. 7.5.1 I2C Interface
        1. 7.5.1.1 I2C Address Selection
        2. 7.5.1.2 I2C General Call
        3. 7.5.1.3 I2C Speed Modes
      2. 7.5.2 Target Mode Operations
        1. 7.5.2.1 Receive Mode
        2. 7.5.2.2 Transmit Mode
      3. 7.5.3 Writing To and Reading From the Registers
      4. 7.5.4 Data Format
  10. 8 Registers
    1. 8.1 Register Map
      1. 8.1.1 Address Pointer Register (address = N/A) [reset = N/A]
      2. 8.1.2 Conversion Register (P[1:0] = 00b) [reset = 0000h]
      3. 8.1.3 Config Register (P[1:0] = 01b) [reset = 8583h]
      4. 8.1.4 Lo_thresh (P[1:0] = 10b) [reset = 8000h] and Hi_thresh (P[1:0] = 11b) [reset = 7FFFh] Registers
  11. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Basic Connections
      2. 9.1.2 Single-Ended Inputs
      3. 9.1.3 Input Protection
      4. 9.1.4 Unused Inputs and Outputs
      5. 9.1.5 Analog Input Filtering
      6. 9.1.6 Connecting Multiple Devices
      7. 9.1.7 Quick-Start Guide
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Shunt Resistor Considerations
        2. 9.2.2.2 Operational Amplifier Considerations
        3. 9.2.2.3 ADC Input Common-Mode Considerations
        4. 9.2.2.4 Resistor (R1, R2, R3, R4) Considerations
        5. 9.2.2.5 Noise and Input Impedance Considerations
        6. 9.2.2.6 First-Order RC Filter Considerations
        7. 9.2.2.7 Circuit Implementation
        8. 9.2.2.8 Results Summary
      3. 9.2.3 Application Curves
  12. 10Power Supply Recommendations
    1. 10.1 Power-Supply Sequencing
    2. 10.2 Power-Supply Decoupling
  13. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  14. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  15. 13Revision History
  16. 14Mechanical, Packaging, and Orderable Information

9.1.5 Analog Input Filtering

Analog input filtering serves two purposes:

  1. Limits the effect of aliasing during the sampling process
  2. Reduces external noise from being a part of the measurement

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 fold back and show up in the actual frequency band of interest below half the sampling frequency. The filter response of the digital filter repeats at multiples of the sampling frequency, also known as the modulator frequency (fMOD), as shown in Figure 9-3. 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.

ADS1113 ADS1114 ADS1115 Effect of AliasingFigure 9-3 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) 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 totally eliminate aliasing, or to reduce the effect of aliasing to a level within 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 ADS111x attenuate signals to a certain degree, as shown in Figure 5-21. In addition, noise components are usually smaller in magnitude than the actual sensor signal. Therefore, use a first-order RC filter with a cutoff frequency set at the output data rate or 10x higher as a generally good starting point for a system design.