SBOS427F June   2017  – March 2021 OPA145 , OPA2145

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: OPA145
    5. 6.5 Thermal Information: OPA2145
    6. 6.6 Electrical Characteristics: VS = 4.5 V to 36 V; ±2.25 V to ±18 V
    7. 6.7 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 Capacitive Load and Stability
      2. 7.3.2 Output Current Limit
      3. 7.3.3 Noise Performance
      4. 7.3.4 Basic Noise Calculations
      5. 7.3.5 Phase-Reversal Protection
      6. 7.3.6 Electrical Overstress
      7. 7.3.7 EMI Rejection
      8. 7.3.8 EMIRR +IN Test Configuration
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
    3. 8.3 System Examples
      1. 8.3.1 16-Bit, 100-kSPS, Fully Differential Transimpedance Imaging and Measurement
  9. 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. 11.1.1.1 TINA-TI™ SImulation Software (Free Download)
        2. 11.1.1.2 WEBENCH Filter Designer Tool
        3. 11.1.1.3 TI Precision Designs
    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

7.3.3 Noise Performance

Figure 7-1 shows the total circuit noise for varying source impedances with the operational amplifier in a unity-gain configuration (with no feedback resistor network and therefore no additional noise contributions). The OPAx145 and OPAx211 are shown with total circuit noise calculated. The op amp contributes both a voltage noise component and a current noise component. The voltage noise is commonly modeled as a time-varying component of the offset voltage. The current noise is modeled as the time-varying component of the input bias current and reacts with the source resistance to create a voltage component of noise. Therefore, the lowest noise op amp for a given application depends on the source impedance. For low source impedance, current noise is negligible, and voltage noise generally dominates. The OPAx145 has both low voltage noise and extremely low current noise because of the FET input of the op amp. As a result, the current noise contribution of the OPAx145 is negligible for any practical source impedance, which makes it the better choice for applications with high source impedance.

GUID-C04CE85C-09A8-4672-93EE-84F84AFDA02E-low.png
NOTE: For a source resistance, RS, greater than 3.8 kΩ, the OPAx145 is a lower-noise option compared to the OPA211, as shown in Figure 7-1.
Figure 7-1 Noise Performance of the OPAx145 and OPA211 in Unity-Gain Buffer Configuration

Equation 1 can be used to calculate the total noise at the output of the amplifier. A plot can be created using this equation to quickly compare the noise performance of two different amplifiers when used with different source resistances, as is shown in Figure 7-1.

Equation 1. GUID-20201012-CA0I-TSWH-FPC1-PJBHBZ3XXHBC-low.gif
where:
  • en = voltage noise
  • In = current noise
  • RS = source impedance
  • k = Boltzmann's constant = 1.38 × 10–23 J/K
  • T = temperature in kelvins (K)

For more details on calculating noise, see Section 7.3.4.