SBOS644C February   2013  – March 2018 INA231

PRODUCTION DATA.  

  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. 8.3.1.1 Power Calculation
        2. 8.3.1.2 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. 8.5.2.1 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. 8.5.5.1 Bus Overview
          1. 8.5.5.1.1 Serial Bus Address
          2. 8.5.5.1.2 Serial Interface
        2. 8.5.5.2 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. 8.6.1.1   AVG Bit Settings [11:9]
          1. Table 5. AVG Bit Settings [11:9] Description
        3. 8.6.1.2   VBUS CT Bit Settings [8:6]
          1. Table 6. VBUS CT Bit Settings [8:6] Description
        4. 8.6.1.3   VSH CT Bit Settings [5:3]
          1. Table 7. Register Description VSH CT Bit Settings [5:3]
        5. 8.6.1.4   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

Configure, Measure, and Calculate Example

In this example, shown in Figure 29, a nominal 10-A load creates a differential voltage of 20 mV across a 2-mΩ shunt resistor. The bus voltage for the INA231 is measured at the external BUS input pin; in this example, BUS is connected to the IN– pin to measure the voltage level delivered to the load. For this example, the BUS pin measures less than 12 V because the voltage at the IN– pin is 11.98 V as a result of the voltage drop across the shunt resistor.

For this example, assuming a maximum expected current of 15 A, the Current_LSB is calculated to be 457.7 μA/bit using Equation 2. Using a value of 500 μA/bit or 1 mA/bit for the Current_LSB significantly simplifies the conversion from the Current register and Power register to amps and watts, respectively. For this example, a value of 1 mA/bit was chosen for the Current register LSB. Using this value for the Current_LSB trades a small amount of resolution for a simpler conversion process on the processor side. Using Equation 1 in this example with a current LSB of 1 mA/bit and a shunt resistor of 2 mΩ results in a Calibration register value of 2560, or A00h.

The Current register (04h) is then calculated by multiplying the decimal value of the Shunt Voltage register contents by the decimal value of the Calibration register and then dividing by 2048, as shown in Equation 3. For this example, the Shunt Voltage register value of 8000 is multiplied by the Calibration register value of 2560 and then divided by 2048 to yield a decimal value for the Current register of 10000, or 2710h. Multiplying this value by 1 mA/bit results in the original 10-A level stated in the example.

Equation 3. INA231 q_curr_shunt_cal_reg_bos547.gif

The LSB for the Bus Voltage register (02h) is a fixed 1.25 mV/bit. This fixed value means that the 11.98 V present at the BUS pin results in a register value of 2570h, or a decimal equivalent of 9584. Note that the MSB of the Bus Voltage register is always zero because the BUS pin is only able to measure positive voltages.

The Power register (03h) is then calculated by multiplying the decimal value of the Current register, 10000, by the decimal value of the Bus Voltage register, 9584, and then dividing by 20,000, as defined in Equation 4. For this example, the result for the Power register is 12B8h, or a decimal equivalent of 4792. Multiplying this result by the power LSB (25 times the [1 × 10–3 Current_LSB]) results in a power calculation of (4792 × 25 mW/bit), or 119.8 W. The Power register LSB has a fixed ratio to the Current register LSB of 25 W/bit to 1 A/bit. For this example, a programmed Current register LSB of 1 mA/bit results in a Power register LSB of 25 mW/bit. This ratio is internally programmed to make sure that the scaling of the power calculation is within an acceptable range. A manual calculation for the power being delivered to the load would use a bus voltage of 11.98 V (12VCM – 20 mV shunt drop) multiplied by the load current of 10 A to give a result of 119.8 W.

Equation 4. INA231 q_power_curr_bos547.gif

Table 1 shows the steps for configuring, measuring, and calculating the values for current and power for this device.

Table 1. Configure, Measure. and Calculate Example(1)

STEP # REGISTER NAME ADDRESS CONTENTS DEC LSB VALUE
Step 1 Configuration 00h 4127h
Step 2 Shunt 01h 1F40h 8000 2.5 µV 20m V
Step 3 Bus 02h 2570h 9584 1.25 mV 11.98 V
Step 4 Calibration 05h A00h 2560
Step 5 Current 04h 2710h 10000 1 mA 10 A
Step 6 Power 03h 12B8h 4792 25 mW 119.8 W
Conditions: Load = 10 A, VCM = 12 V, RSHUNT = 2 mΩ, and VBUS =11.98 V.