SBOSA30D March   2022  – December 2024

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Amplifier Input Common-Mode Signal
        1. 7.3.1.1 Enhanced PWM Rejection Operation
        2. 7.3.1.2 Input-Signal Bandwidth
        3. 7.3.1.3 Low Input Bias Current
        4. 7.3.1.4 Low VSENSE Operation
        5. 7.3.1.5 Wide Fixed Gain Output
        6. 7.3.1.6 Wide Supply Range
    4. 7.4 Device Functional Modes
      1. 7.4.1 Adjusting the Output With the Reference Pins
      2. 7.4.2 Reference Pin Connections for Unidirectional Current Measurements
        1. 7.4.2.1 Ground Referenced Output
        2. 7.4.2.2 VS Referenced Output
      3. 7.4.3 Reference Pin Connections for Bidirectional Current Measurements
        1. 7.4.3.1 Output Set to External Reference Voltage
        2. 7.4.3.2 Output Set to Mid-Supply Voltage
        3. 7.4.3.3 Output Set to Mid-External Reference
        4. 7.4.3.4 Output Set Using Resistor Divider
      4. 7.4.4 High Signal Throughput
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 RSENSE and Device Gain Selection
    2. 8.2 Typical Application
      1. 8.2.1 Inline Motor Current-Sense Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
    3. 8.3 Power Supply Recommendations
      1. 8.3.1 Power Supply Decoupling
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Examples
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

8.1.1 RSENSE and Device Gain Selection

The accuracy of any current-sense amplifier is maximized by choosing the largest current-sense resistor value possible. A larger value 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 value can be in a given application because of the physical dimensions of the package, package construction, and maximum power dissipation. Equation 2 gives the maximum value for the current-sense resistor for a given power dissipation budget:

Equation 2. INA241A INA241B

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 exceeding the positive swing limitation.

Equation 3. INA241A INA241B

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 of the device as specified in the Specifications.

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 under consideration. If the sense resistor selected for the maximum power dissipation is too large, then selecting a lower gain device is possible to avoid positive swing limitations.

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

Equation 4. INA241A INA241B

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 as specified in the Specifications.

Table 8-1 shows an example of the different results obtained from using five different gain versions of the INA241x. From the table data, the highest gain device allows a smaller current-shunt resistor and decreased power dissipation in the element.

Table 8-1 RSENSE Selection and Power Dissipation(1)
PARAMETEREQUATIONRESULTS AT VS = 5V
A1, B1 DEVICESA2, B2 DEVICESA3, B3 DEVICESA4, B4 DEVICESA5, B5 DEVICES
GGain10V/V20V/V50V/V100V/V200V/V
VSENSEIdeal differential input voltageVSENSE = VOUT / G500mV250mV100mV50mV25mV
RSENSECurrent sense resistor valueRSENSE = VSENSE / IMAX50mΩ25mΩ10mΩ5mΩ2.5mΩ
PSENSECurrent-sense resistor power dissipationRSENSE × IMAX25W2.5W1W0.5W0.25W
(1) Design example with 10A full-scale current with maximum output voltage set to 5V.