SBOSAK8 March   2025 INA950-SEP

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
    6. 5.6 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 Amplifier Input Common-Mode Range
      2. 6.3.2 Input-Signal Bandwidth
      3. 6.3.3 Low Input Bias Current
      4. 6.3.4 Low VSENSE Operation
      5. 6.3.5 Wide Fixed-Gain Output
    4. 6.4 Device Functional Modes
      1. 6.4.1 Unidirectional Operation
      2. 6.4.2 High Signal Throughput
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 RSENSE and Device Gain Selection
      2. 7.1.2 Input Filtering
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Overload Recovery With Negative VSENSE
      3. 7.2.3 Application Curve
    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 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
    1. 10.1 Mechanical Data

7.1.1 RSENSE and Device Gain Selection

The accuracy of any current-sense amplifier is maximized by choosing the current-sense resistor to be as large as possible. 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 because of the resistor size and maximum allowable power dissipation. Equation 1 gives the maximum value for the current-sense resistor for a given power dissipation budget:

Equation 1. INA950-SEP

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 results from the power-supply voltage, VS, and device swing-to-rail limitations. To verify that the current-sense signal is properly passed to the output, both positive and negative output swing limitations must be examined. Equation 2 provides the maximum values of RSENSE and GAIN to keep the device from exceeding the positive swing limitation.

Equation 2. INA950-SEP

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 as specified in this data sheet.

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 3 provides the limit on the minimum value of the sense resistor.

Equation 3. INA950-SEP

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.

Table 7-1 shows an example of the different results obtained from using five different gain versions of the INA950-SEP. From the table data, the highest gain device allows a smaller current-shunt resistor and decreased power dissipation in the element.

Table 7-1 RSENSE Selection and Power Dissipation
PARAMETER(1) EQUATION RESULTS
VS Supply Voltage 5V
G Gain 20V/V
VSENSE Ideal differential input voltage (Ignores swing limitation and power-supply variation.) VSENSE = VOUT / G 250mV
RSENSE Current-sense resistor value RSENSE = VSENSE / IMAX 25mΩ
PSENSE Current-sense resistor power dissipation RSENSE x IMAX2 2.5 W
(1) Design example with 10A, full-scale current with maximum output voltage set to 5V.