SBOS644C February   2013  – March 2018 INA231


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      High-or Low-Side Sensing
  4. Revision History
  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 Timing Requirements: I2C Bus
    7. 7.7 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Basic Analog-to-Digital Converter (ADC) Functions
        1. Power Calculation
        2. ALERT Pin
    4. 8.4 Device Functional Modes
      1. 8.4.1 Averaging and Conversion Time Considerations
    5. 8.5 Programming
      1. 8.5.1 Configure, Measure, and Calculate Example
      2. 8.5.2 Programming the Power Measurement Engine
        1. Calibration Register and Scaling
      3. 8.5.3 Simple Current Shunt Monitor Usage (No Programming Necessary)
      4. 8.5.4 Default INA231 Settings
      5. 8.5.5 Writing to and Reading from the INA231
        1. Bus Overview
          1. Serial Bus Address
          2. Serial Interface
        2. High-Speed I2C Mode
      6. 8.5.6 SMBus Alert Response
    6. 8.6 Register Maps
      1. Table 3. Summary of Register Set
      2. 8.6.1     Configuration Register (00h, Read/Write)
        1. Table 4. Configuration Register (00h, Read/Write) Descriptions
        2.   AVG Bit Settings [11:9]
          1. Table 5. AVG Bit Settings [11:9] Description
        3.   VBUS CT Bit Settings [8:6]
          1. Table 6. VBUS CT Bit Settings [8:6] Description
        4.   VSH CT Bit Settings [5:3]
          1. Table 7. Register Description VSH CT Bit Settings [5:3]
        5.   Mode Settings [2:0]
          1. Table 8. Mode Settings [2:0]
      3. 8.6.2     Shunt Voltage Register (01h, Read-Only)
        1. Table 9. Shunt Voltage Register (01h, Read-Only) Description
      4. 8.6.3     Bus Voltage Register (02h, Read-Only)
        1. Table 10. Bus Voltage Register (02h, Read-Only) Description
      5. 8.6.4     Power Register (03h, Read-Only)
        1. Table 11. Power Register (03h, Read-Only) Description
      6. 8.6.5     Current Register (04h, Read-Only)
        1. Table 12. Current Register (04h, Read-Only) Description
      7. 8.6.6     Calibration Register (05h, Read/Write)
        1. Table 13. Calibration Register (05h, Read/Write) Description
      8. 8.6.7     Mask/Enable Register (06h, Read/Write)
        1. Table 14. Mask/Enable Register (06h, Read/Write) Description
      9. 8.6.8     Alert Limit Register (07h, Read/Write)
        1. Table 15. Alert Limit Register (07h, Read/Write) Description
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Filtering and Input Considerations
    2. 9.2 Typical Applications
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • YFF|12
  • YFD|12
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Filtering and Input Considerations

Measuring current is often a noisy task, and such noise can be difficult to define. The INA231 offers several options for filtering by allowing the conversion times and number of averages to be independently selected in the Configuration register. The conversion times can be independently set for the shunt voltage and bus voltage measurements to allow added flexibility in configuring the monitoring of the power-supply bus.

The internal ADC is based on a delta-sigma (ΔΣ) front-end with a 500-kHz (±30%) typical sampling rate. This architecture has good inherent noise rejection; however, transients that occur at or very close to the sampling rate harmonics can cause problems. These signals are at 1 MHz and higher; therefore, manage them by incorporating filtering at the input of the INA231. The high frequency enables the use of low-value series resistors on the filter with negligible effects on measurement accuracy. In general, filtering the INA231 input is only necessary if there are transients at exact harmonics of the 500-kHz (±30%) sampling rate (greater than 1 MHz). Filter using the lowest possible series resistance (typically 10 Ω or less) and a ceramic capacitor. Recommended values for this capacitor are 0.1 μF to 1.0 μF. Figure 28 shows the INA231 with an additional filter added at the input.

INA231 ai_input_filtering_bos601.gifFigure 28. INA231 With Input Filtering

Overload conditions are another consideration for the INA231 inputs. The INA231 inputs are specified to tolerate 30 V across the inputs. A large differential scenario might be a short to ground on the load side of the shunt. This type of event can result in full power-supply voltage across the shunt (as long as the power supply or energy storage capacitors support it). Keep in mind that removing a short to ground can result in inductive kickbacks that could exceed the 30-V differential and common-mode rating of the INA231. Inductive kickback voltages are best controlled by zener-type transient-absorbing devices (commonly called transzorbs) combined with sufficient energy storage capacitance.

In applications that do not have large energy-storage electrolytics on one or both sides of the shunt, an input overstress condition may result from an excessive dV/dt of the voltage applied to the input. A hard physical short is the most likely cause of this event, particularly in applications with no large electrolytics present. This problem occurs because an excessive dV/dt can activate the ESD protection in the INA231 in systems where large currents are available. Testing has demonstrated that the addition of 10-Ω resistors in series with each input of the INA231 sufficiently protect the inputs against this dV/dt failure up to the 30-V rating of the INA231. Selecting these resistors in the range noted has minimal effect on accuracy.