JAJSLE9A March   2023  – April 2024 OPA928

PRODUCTION DATA  

  1.   1
  2. 1 特長
  3. 2 アプリケーション
  4. 3 概要
  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™シミュレーション・ソフトウェア (無償ダウンロード)
        3. 8.1.1.3 TI のリファレンス・デザイン
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 ドキュメントの更新通知を受け取る方法
    4. 8.4 サポート・リソース
    5. 8.5 Trademarks
    6. 8.6 静電気放電に関する注意事項
    7. 8.7 用語集
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7.2.1 High-Impedance Amplifier

The OPA928 behaves very close to an ideal op amp in regards to the input current. The near-zero input bias current performance enables applications with extremely high impedance signal sources. For example, pH probes can have an output impedance of up to 10GΩ. Most op amps are inadequate to use with this kind of sensor impedance. For example, a CMOS op amp with 1pA of input bias current loads the sensor and causes a large, and unacceptable, 10mV error at the input at room temperature. This error can increase exponentially across the industrial temperature range. In Figure 7-7, the OPA928 is used as a high-impedance electrometer to amplify the small signal from the pH probe sensor. The high input impedance and ultra-low bias current into the positive input pin of the OPA928 does not load the sensor and minimizes the input bias current error.

OPA928 High Impedance pH Probe Amplifier Circuit Figure 7-7 High Impedance pH Probe Amplifier Circuit