SBOSA65 July   2021 OPA396


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Low Input Bias Current
      2. 7.3.2 Input Differential Voltage
      3. 7.3.3 Capacitive Load Drive
      4. 7.3.4 EMI Rejection
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Three-Terminal CO Gas Sensor
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curve
      2. 8.2.2 4-mA to 20-mA Loop Design
        1. Design Requirements
        2. Application Curve
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. TINA-TI™ Simulation Software (Free Download)
    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
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Three-Terminal CO Gas Sensor

Figure 8-1 shows a simple micropower potentiostat circuit for use with three-terminal unbiased CO sensors. This same design is applicable to many other type of three-terminal gas sensors or electrochemical cells. The basic sensor has three electrodes: the sense or working electrode (WE), counter electrode (CE) and reference electrode (RE). A current flows between CE and WE proportional to the detected concentration. The RE monitors the potential of the internal reference point. For an unbiased sensor, the WE and RE must be maintained at the same potential by adjusting the bias on CE. Through the potentiostat circuit formed by U1, the servo feedback action maintains the RE pin at a potential set by VREF. R1 maintains stability as a result of the large capacitance of the sensor. C1 and R2 form the potentiostat integrator and set the feedback time constant. U2 forms a transimpedance amplifier (TIA) to convert the resulting sensor current into a proportional voltage. The transimpedance gain, and resulting sensitivity, is set by RF according to Equation 1:

Equation 1. VTIA = (–I * RF) + VREF

RLoad is a load resistor with a value that is normally specified by the sensor manufacturer (typically, 10 Ω). The potential at WE is set by the applied VREF.

GUID-20210720-CA0I-FDKF-JN5S-MLKMQJR9PSHX-low.gif Figure 8-1 Three-Terminal CO Gas Sensor