SBOSA77A March   2023  – April 2024 OPA928

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 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: 4.5V ≤ VS < 8V
    6. 5.6 Electrical Characteristics: 8V ≤ VS ≤ 16V
    7. 5.7 Electrical Characteristics: 16V < VS ≤ 36V
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Guard Buffer
      2. 6.3.2 Input Protection
      3. 6.3.3 Thermal Protection
      4. 6.3.4 Capacitive Load and Stability
      5. 6.3.5 EMI Rejection
      6. 6.3.6 Common-Mode Voltage Range
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Contamination Considerations
      2. 7.1.2 Guarding Considerations
      3. 7.1.3 Single-Supply Considerations
      4. 7.1.4 Humidity Considerations
      5. 7.1.5 Dielectric Relaxation
      6. 7.1.6 Shielding
    2. 7.2 Typical Applications
      1. 7.2.1 High-Impedance Amplifier
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curve
      2. 7.2.2 Transimpedance Amplifier
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
          1. 7.2.2.2.1 Input Bias
          2. 7.2.2.2.2 Offset Voltage
          3. 7.2.2.2.3 Stability
          4. 7.2.2.2.4 Noise
      3. 7.2.3 Improved Diode Limiter
      4. 7.2.4 Instrumentation Amplifier
    3. 7.3 Power-Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Examples
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 PSpice® for TI
        2. 8.1.1.2 TINA-TI™ Simulation Software (Free Download)
        3. 8.1.1.3 TI Reference Designs
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.1.3 Single-Supply Considerations

Some applications require consideration of the limitations of the guard buffer output swing. One such application is the single-supply inverting amplifier with a common-mode voltage equal to the rail, most commonly ground. The guard buffer cannot drive the guard all the way to the rail. The internal guard buffer features a rail-to-rail output stage and is capable of driving the guard to within 15mV of the rail. The small voltage difference manifests as a differential voltage across the antiparallel diodes as shown in Figure 7-3. Even a small differential voltage of 15mV can cause a significant amount of leakage through the diodes at high temperatures.

GUID-20240314-SS0I-8GQX-5GM6-CR0FZSRM0SPD-low.svg Figure 7-3 Single-Supply Transimpedance Amplifier
To avoid the input common-mode limitation of the guard buffer in inverting configurations with zero-common mode voltage, connect the guard pins directly to ground as done in Figure 7-4.
GUID-20240314-SS0I-CFMZ-0X70-JNZLSS1HCLCV-low.svg Figure 7-4 Single-Supply Transimpedance Amplifier With Grounded Guard Pin

Figure 7-5 shows the input bias current performance of the OPA928 near the negative rail when the guard pins are left floating compared to when the guard pins are tied to ground.

GUID-20240325-SS0I-J98V-F83D-2SRSHKTSJRBD-low.svg Figure 7-5 Input Bias Current Near the Negative Rail in Single Supply Applications

Noninverting, high-gain configurations can be susceptible to similar limitations. The limitation occurs when the input signal is less than the specified output swing of the guard buffer. To circumvent this issue, consider using dual supplies.