JAJSR73 February   2024 INA185-Q1

PRODUCTION DATA  

  1.   1
  2. 特長
  3. アプリケーション
  4. 概要
  5. Pin Configuration and Functions
  6. 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
  7. Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 High Bandwidth and Slew Rate
      2. 6.3.2 Bidirectional Current Monitoring
      3. 6.3.3 Wide Input Common-Mode Voltage Range
      4. 6.3.4 Precise Low-Side Current Sensing
      5. 6.3.5 Rail-to-Rail Output Swing
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Mode
      2. 6.4.2 Unidirectional Mode
      3. 6.4.3 Bidirectional Mode
      4. 6.4.4 Input Differential Overload
      5. 6.4.5 Shutdown Mode
  8. Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Basic Connections
      2. 7.1.2 RSENSE and Device Gain Selection
      3. 7.1.3 Signal Filtering
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curve
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Common-Mode Transients Greater Than 26V
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
    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. 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

RSENSE and Device Gain Selection

User can choose a current-sense resistor that is as large as possible to maximize the accuracy of the INA185-Q1. A large sense resistor maximizes the differential input signal for a given amount of current flow and reduces the error contribution of the offset voltage. However, there are practical limits as to how large the current-sense resistor can be in a given application. The INA185-Q1 has a typical input bias current of 75µA for each input when operated at a 12V common-mode voltage input. When large current-sense resistors are used, these bias currents cause increased offset error and reduced common-mode rejection. Therefore, using current-sense resistors larger than a few ohms is generally not recommended for applications that require current-monitoring accuracy. Another common restriction on the value of the current-sense resistor is the maximum allowable power dissipation that is budgeted for the resistor. Equation 2 gives the maximum value for the current sense resistor for a given power dissipation budget:

Equation 2. GUID-D22B6BBC-6DF1-468C-A29D-92424755A1B3-low.gif

where:

  • PDMAX is the maximum allowable power dissipation in RSENSE.
  • IMAX is the maximum current that flows through RSENSE.

An additional limitation on the size of the current-sense resistor and device gain is due to the power-supply voltage, VS, and device swing-to-rail limitations. To make sure that the current-sense signal is properly passed to the output, both positive and negative output swing limitations must be examined. Equation 3 provides the maximum values of RSENSE and GAIN to keep the device from hitting the positive swing limitation.

Equation 3. GUID-F8F39180-91E2-4717-82A7-46213FF2E79D-low.gif

where:

  • IMAX is the maximum current that flows through RSENSE.
  • GAIN is the gain of the current sense-amplifier.
  • VSP is the positive output swing specified in the data sheet.
  • VREF is the externally applied voltage on the REF pin.

To avoid positive output swing limitations when selecting the value of RSENSE, there is always a trade-off between the value of the sense resistor and the gain of the device to consider. If the sense resistor selected for the maximum power dissipation is too large, then selecting a lower-gain device to avoid positive swing limitations is possible.

The negative swing limitation places a limit on how small of a sense resistor can be used in a given application. Equation 4 provides the limit on the minimum size of the sense resistor.

Equation 4. GUID-CB03E871-5ACB-406D-B3B2-BCA94F3BB636-low.gif

where:

  • IMIN is the minimum current that flows through RSENSE.
  • GAIN is the gain of the current sense amplifier.
  • VSN is the negative output swing of the device (see Rail-to-Rail Output Swing).
  • VREF is the externally applied voltage on the REF pin.

In addition to adjusting the offset and gain, the voltage applied to the REF pin can be slightly increased to avoid negative swing limitations.