JAJSCL0B July   2016  – February 2018 INA240


  1. 特長
  2. アプリケーション
  3. 概要
    1.     代表的なアプリケーション
    2.     強化されたPWM除去
  4. 改訂履歴
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Amplifier Input Signal
        1. Enhanced PWM Rejection Operation
        2. Input Signal Bandwidth
      2. 8.3.2 Selecting the Sense Resistor (RSENSE)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Adjusting the Output Midpoint With the Reference Pins
      2. 8.4.2 Reference Pin Connections for Unidirectional Current Measurements
        1. Ground Referenced Output
        2. VS Referenced Output
      3. 8.4.3 Reference Pin Connections for Bidirectional Current Measurements
        1. Output Set to External Reference Voltage
        2. Output Set to Midsupply Voltage
        3. Output Set to Mid-External Reference
        4. Output Set Using Resistor Divider
      4. 8.4.4 Calculating Total Error
        1. Error Sources
        2. Reference Voltage Rejection Ratio Error
          1. Total Error Example 1
          2. Total Error Example 2
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Input Filtering
    2. 9.2 Typical Applications
      1. 9.2.1 Inline Motor Current-Sense Application
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curve
      2. 9.2.2 Solenoid Drive Current-Sense Application
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curve
    3. 9.3 Do's and Don'ts
      1. 9.3.1 High-Precision Applications
      2. 9.3.2 Kelvin Connection from the Current-Sense Resistor
  10. 10Power Supply Recommendations
    1. 10.1 Power Supply Decoupling
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Connection to the Current-Sense Resistor
    2. 11.2 Layout Example
  12. 12デバイスおよびドキュメントのサポート
    1. 12.1 ドキュメントのサポート
      1. 12.1.1 関連資料
    2. 12.2 関連リンク
    3. 12.3 ドキュメントの更新通知を受け取る方法
    4. 12.4 コミュニティ・リソース
    5. 12.5 商標
    6. 12.6 静電気放電に関する注意事項
    7. 12.7 Glossary
  13. 13メカニカル、パッケージ、および注文情報



Selecting the Sense Resistor (RSENSE)

The INA240 determines the current magnitude from measuring the differential voltage developed across a resistor. This resistor is referred to as a current-sensing resistor or a current-shunt resistor. The flexible design of the device allows a wide input signal range across this current-sensing resistor.

The current-sensing resistor is ideally chosen solely based on the full-scale current to be measured, the full-scale input range of the circuitry following the device, and the device gain selected. The minimum current-sensing resistor is a design-based decision in order to maximize the input range of the signal chain circuitry. Full-scale output signals that are not maximized to the full input range of the system circuitry limit the ability of the system to exercise the full dynamic range of system control.

Two important factors to consider when finalizing the current-sensing resistor value are: the required current measurement accuracy and the maximum power dissipation across the resistor. A larger resistor voltage provides for a more accurate measurement, but increases the power dissipation in the resistor. The increased power dissipation generates heat, which reduces the sense resistor accuracy because of the temperature coefficient. The voltage signal measurement uncertainty is reduced when the input signal gets larger because any fixed errors become a smaller percentage of the measured signal. The design trade-off to improve measurement accuracy increases the current-sensing resistor value. The increased resistance value results in an increased power dissipation in the system which can additionally decrease the overall system accuracy. Based on these relationships, the measurement accuracy is inversely proportional to both the resistance value and power dissipation contributed by the current-shunt selection.

By increasing the current-shunt resistor, the differential voltage is increased across the resistor. Larger input differential voltages require a smaller amplifier gain to achieve a full-scale amplifier output voltage. Smaller current-shunt resistors are desired but require large amplifier gain settings. The larger gain settings often have increased error and noise parameters, which are not attractive for precision designs. Historically, the design goals for high-performance measurements forced designers to accept selecting larger current-sense resistors and the lower gain amplifier settings. The INA240 provides 100-V/V and 200-V/V gain options that offer the high-gain setting and maintains high-performance levels with offset values below 25 µV. These devices allow for the use of lower shunt resistor values to achieve lower power dissipation and still meet high system performance specifications.

Table 1 shows an example of the different results obtained from using two different gain versions of the INA240. From the table data, the higher gain device allows a smaller current-shunt resistor and decreased power dissipation in the element. The Calculating Total Error section provides information on the error calculations that must be considered in addition to the gain and current-shunt value when designing with the INA240.

Table 1. RSENSE Selection and Power Dissipation(1)

INA240A1 INA240A4
Gain 20 V/V 200 V/V
VDIFF Ideal maximum differential input voltage VDIFF = VOUT / Gain 150 mV 15 mV
RSENSE Current-sense resistor value RSENSE = VDIFF / IMAX 15 mΩ 1.5 mΩ
PRSENSE Current-sense resistor power dissipation RSENSE × IMAX2 1.5 W 0.15 W
Full-scale current = 10 A, and full-scale output voltage = 3 V.