SLYS025B January   2021  – May 2025 INA238

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 Timing Requirements (I2C)
    7. 5.7 Timing Diagram
    8. 5.8 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 Versatile High Voltage Measurement Capability
      2. 6.3.2 Power Calculation
      3. 6.3.3 Low Bias Current
      4. 6.3.4 High-Precision Delta-Sigma ADC
        1. 6.3.4.1 Low Latency Digital Filter
        2. 6.3.4.2 Flexible Conversion Times and Averaging
      5. 6.3.5 Integrated Precision Oscillator
      6. 6.3.6 Multi-Alert Monitoring and Fault Detection
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown Mode
      2. 6.4.2 Power-On Reset
    5. 6.5 Programming
      1. 6.5.1 I2C Serial Interface
        1. 6.5.1.1 Writing to and Reading Through the I2C Serial Interface
        2. 6.5.1.2 High-Speed I2C Mode
        3. 6.5.1.3 SMBus Alert Response
    6. 6.6 Register Maps
      1. 6.6.1 INA238 Registers
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Device Measurement Range and Resolution
      2. 7.1.2 Current and Power Calculations
      3. 7.1.3 ADC Output Data Rate and Noise Performance
      4. 7.1.4 Input Filtering Considerations
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Select the Shunt Resistor
        2. 7.2.2.2 Configure the Device
        3. 7.2.2.3 Program the Shunt Calibration Register
        4. 7.2.2.4 Set Desired Fault Thresholds
        5. 7.2.2.5 Calculate Returned Values
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.1.2 Current and Power Calculations

For the INA238 device to report current values in Ampere units, a constant conversion value must be written in the SHUNT_CAL register that is dependent on the maximum measured current and the shunt resistance used in the application. The SHUNT_CAL register is calculated based on the first equation in this section. The term CURRENT_LSB is the LSB step size for the CURRENT register where the current in Amperes is stored. The value of CURRENT_LSB is based on the maximum expected current as shown in the second equation in this section. This value directly defines the resolution of the CURRENT register. While the smallest CURRENT_LSB value yields highest resolution, selecting a higher round-number (no higher than 8x) value for the CURRENT_LSB is common for simplifying the conversion of the CURRENT.

The RSHUNT term is the resistance value of the external shunt used to develop the differential voltage across the IN+ and IN– pins. Use the following equation for ADCRANGE = 0. For ADCRANGE = 1, the value of SHUNT_CAL must be multiplied by 4.

Equation 1. S H U N T _ C A L = 819.2 × 10 6 × C U R E N T _ L S B × R S H U N T

where

  • 819.2 × 106 is an internal fixed value used to verify that scaling is maintained properly.
  • the value of SHUNT_CAL must be multiplied by 4 for ADCRANGE = 1.

 

Equation 2. C u r r e n t _ L S B   = M a x i m u m   E x p e c t e d   C u r r e n t 2 15

Note that the current is calculated following a shunt voltage measurement based on the value set in the SHUNT_CAL register. If the value loaded into the SHUNT_CAL register is zero, the current value reported through the CURRENT register is also zero.

After programming the SHUNT_CAL register with the calculated value, the measured current in Amperes can be read from the CURRENT register. The final value is scaled by CURRENT_LSB and calculated in the following equation:

Equation 3. C u r r e n t   A = C U R R E N T _ L S B × C U R R E N T

where

  • CURRENT is the value read from the CURRENT register

The power value can be read from the POWER register as a 24-bit value and converted to Watts by using the following equation:

 

Equation 4. P o w e r   W = 0.2 × C U R R E N T _ L S B × P O W E R

where

  • POWER is the value read from the POWER register.
  • CURRENT_LSB is the lsb size of the current calculation as defined by Equation 2.

 

For a design example using these equations refer to Section 7.2.2.