Corrected_Full_Scale_Cal = trunc

Cal

MeasShuntCurrent

INA231_Current

´

Current

BusVoltage

20,000

·

Power =

INA231

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SBOS644 – FEBRUARY 2013

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

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 ensure that the scaling of the power calculation is within an acceptable range. A

shunt drop) multiplied by the load current of 10 A to give a result of 119.8 W.

(4)

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

device.

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

(1)

PROGRAMMING THE INA231 POWER MEASUREMENT ENGINE

Calibration Register and Scaling

The Calibration register makes it possible to set the scaling of the Current and Power registers to the values that

are most useful for a given application. One strategy may be to set the Calibration register so that the largest

possible number is generated in the Current register or Power register at the expected full-scale point. This

approach yields the highest resolution based on the previously-calculated minimum Current_LSB in the equation

for the Calibration register (Equation 1). The Calibration register can also be selected to provide values in the

Current and Power registers that either provide direct decimal equivalents of the values being measured, or yield

a round LSB value for each corresponding register. After these choices have been made, the Calibration register

also offers possibilities for end-user, system-level calibration. By physically measuring the current with an

external ammeter, the exact current is known. The value of the Calibration register can then be adjusted based

on the measured current result of the INA231 to cancel the total system error, as shown in Equation 5.

(5)

Copyright © 2013, Texas Instruments Incorporated

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