SBOS743A July   2015  – May 2020 INA226-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      High-Side or Low-Side Sensing Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 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
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Basic ADC Functions
        1. 7.3.1.1 Power Calculation
        2. 7.3.1.2 Alert Pin
    4. 7.4 Device Functional Modes
      1. 7.4.1 Averaging and Conversion Time Considerations
      2. 7.4.2 Filtering and Input Considerations
    5. 7.5 Programming
      1. 7.5.1 Programming the Calibration Register
      2. 7.5.2 Programming the Power Measurement Engine
        1. 7.5.2.1 Calibration Register and Scaling
      3. 7.5.3 Simple Current Shunt Monitor Usage (No Programming Necessary)
      4. 7.5.4 Default Settings
      5. 7.5.5 Bus Overview
        1. 7.5.5.1 Serial Bus Address
        2. 7.5.5.2 Serial Interface
        3. 7.5.5.3 Writing to and Reading from the INA226-Q1
          1. 7.5.5.3.1 High-Speed I2C Mode
        4. 7.5.5.4 SMBus Alert Response
    6. 7.6 Register Maps
      1. Table 4. Register Set Summary
      2. 7.6.1    Configuration Register (00h) (Read/Write)
        1. Table 5. Configuration Register (00h) (Read/Write) Descriptions
      3. 7.6.2    Shunt Voltage Register (01h) (Read-Only)
        1. Table 10. Shunt Voltage Register (01h) (Read-Only) Description
      4. 7.6.3    Bus Voltage Register (02h) (Read-Only)
        1. Table 11. Bus Voltage Register (02h) (Read-Only) Description
      5. 7.6.4    Power Register (03h) (Read-Only)
        1. Table 12. Power Register (03h) (Read-Only) Description
      6. 7.6.5    Current Register (04h) (Read-Only)
        1. Table 13. Current Register (04h) (Read-Only) Register Description
      7. 7.6.6    Calibration Register (05h) (Read/Write)
        1. Table 14. Calibration Register (05h) (Read/Write) Description
      8. 7.6.7    Mask/Enable Register (06h) (Read/Write)
        1. Table 15. Mask/Enable Register (06h) (Read/Write)
      9. 7.6.8    Alert Limit Register (07h) (Read/Write)
        1. Table 16. Alert Limit Register (07h) (Read/Write) Description
      10. 7.6.9    Manufacturer ID Register (FEh) (Read-Only)
        1. Table 17. Manufacturer ID Register (FEh) (Read-Only) Description
      11. 7.6.10   Die ID Register (FFh) (Read-Only)
        1. Table 18. Die ID Register (FFh) (Read-Only) Description
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 High-Side Sensing Circuit Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
          1. Table 19. Configuration Register (00h) Settings for (Value = 4025h)
          2. Table 20. Configuration Register (00h) Settings for (Value = 4005h)
          3. Table 21. Mask/Enable Register (06h) Settings for and (Value = 8000h)
          4. Table 22. Alert Limit Register (07h) Settings for and (Value = 7D00)
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7.5.1 Programming the Calibration Register

Figure 27 shows a nominal 10-A load that creates a differential voltage of 20 mV across a 2-mΩ shunt resistor. The bus voltage for the INA226-Q1 is measured at the external VBUS input pin, which in this example is connected to the IN– pin to measure the voltage level delivered to the load. For this example, the VBUS 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 for the Current_LSB of 500 μA/Bit or 1 mA/Bit would significantly simplify the conversion from the Current Register (04h) and Power Register (03h) to amperes and watts. For this example, a value of 1 mA/bit was chosen for the Current_LSB. Using this value for the Current_LSB does trade a small amount of resolution for having a simpler conversion process on the user side. Using Equation 1 in this example with a Current_LSB value 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 (01h) 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 contains a value of 8,000 (representing 20 mV), which is multiplied by the Calibration Register value of 2560 and then divided by 2048 to yield a decimal value for the Current Register (04h) of 10000, or 2710h. Multiplying this value by 1 mA/bit results in the original 10-A level stated in the example.

Equation 3. INA226-Q1 q_curr_shunt_cal_reg_bos547.gif

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

The Power Register (03h) is then be calculated by multiplying the decimal value of the Current Register, 10000, by the decimal value of the Bus Voltage Register (02h), 9584, and then dividing by 20,000, as defined in Equation 4. For this example, the result for the Power Register (03h) 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 119.82 W. The power LSB has a fixed ratio to the Current_LSB of 25. For this example, a programmed 1 mA/bit Current_LSB results in a power LSB of 25 mW/bit. This ratio is internally programmed to ensure 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 (12 VCM – 20 mV shunt drop) multiplied by the load current of 10 A to give a result of 119.8 W.

Equation 4. INA226-Q1 q_power_curr_bos547.gif

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

Table 1. Calculating Current and Power(1)

STEP REGISTER NAME ADDRESS CONTENTS DEC LSB VALUE
Step 1 Configuration Register 00h 4127h — — —
Step 2 Shunt Register 01h 1F40h 8000 2.5 µV 20 mV
Step 3 Bus Voltage Register 02h 2570h 9584 1.25 mV 11.98 V
Step 4 Calibration Register 05h A00h 2560 — —
Step 5 Current Register 04h 2710 10000 1 mA 10 A
Step 6 Power Register 03h 12B8h 4792 25 mW 119.82 W
(1) Conditions: Load = 10 A, VCM = 12 V, RSHUNT = 2 mΩ, and VVBUS = 12 V.