SBOSA29A June   2020  – November 2023 INA281

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 Signal
        1. 6.3.1.1 Input-Signal Bandwidth
        2. 6.3.1.2 Low Input Bias Current
        3. 6.3.1.3 Low VSENSE Operation
        4. 6.3.1.4 Wide Fixed Gain Output
        5. 6.3.1.5 Wide Supply Range
    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
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

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

where:

  • PDMAX is the maximum allowable power dissipation in RSENSE.
  • IMAX is the maximum current that will flow 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 2 provides the maximum values of RSENSE and GAIN to keep the device from exceeding the positive swing limitation.

Equation 2. GUID-481DE8B6-7634-486D-94D7-9FAB6BAA6C7A-low.gif

where:

  • IMAX is the maximum current that will flow through RSENSE.
  • GAIN is the gain of the current-sense amplifier.
  • VSP is the positive output swing as specified in the 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 it is possible to select a lower-gain device 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. GUID-B96769C5-71F0-4A94-8E7C-F00500978F8A-low.gif

where:

  • IMIN is the minimum current that will flow 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 INA281-Q1. 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(1)
PARAMETEREQUATIONRESULTS AT VS = 5 V
A1, B1 DEVICESA2, B2 DEVICESA3, B3 DEVICESA4, B4 DEVICESA5, B5 DEVICES
GGain20 V/V50 V/V100 V/V200 V/V500 V/V
VDIFFIdeal differential input voltageVDIFF = VOUT / G250 mV100 mV50 mV25 mV10 mV
RSENSECurrent sense resistor valueRSENSE = VDIFF / IMAX25 mΩ10 mΩ5 mΩ2.5 mΩ1 mΩ
PSENSECurrent-sense resistor power dissipationRSENSE × IMAX22.5 W1 W0.5W0.25 W0.1 W
(1) Design example with 10-A full-scale current with maximum output voltage set to 5 V.