ZHCSLG0A June 2020 – June 2021 INA238-Q1
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3 Feature Description
- 7.4 Device Functional Modes
- 7.5 Programming
- 7.6 Register Maps
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
8.1.2 Current and Power Calculations
For the INA238-Q1 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 Equation 1. 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 Equation 2, and it directly defines the resolution of the CURRENT register. While the smallest CURRENT_LSB value yields highest resolution, it is common to select a higher round-number (no higher than 8x) value for the CURRENT_LSB in order to simplify 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 Equation 1 for ADCRANGE = 0. For ADCRANGE = 1, the value of SHUNT_CAL must be multiplied by 4.
where
- 819.2 x 106 is an internal fixed value used to ensure scaling is maintained properly.
- the value of SHUNT_CAL must be multiplied by 4 for ADCRANGE = 1.
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 Equation 3:
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 Equation 4:
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 8.2.2.