Current

BusVoltage

20,000

·

Power =

Corrected_Full_Scale_Cal = trunc

Cal

MeasShuntCurrent

INA226_Current

´

INA226

SBOS547

– JUNE 2011

www.ti.com

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, 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

25mW/bit), or 119.82W. The power LSB has a fixed ratio to the current LSB of 25W/bit to 1A/bit. For this

example, a programmed 1mA/bit current LSB results in a power LSB of 25mW/bit. This ratio is internally

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

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

(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

20mV

Step 3

Bus

02h

2570h

9584

1.25mV

11.98V

Step 4

Calibration

05h

A00h

2560

—

—

Step 5

Current

04h

2710

10000

1mA

10A

Step 6

Power

03h

12B8h

4792

25mW

119.82W

(1)

PROGRAMMING THE INA226 POWER MEASUREMENT ENGINE

Calibration Register and Scaling

The Calibration Register makes it possible to set the scaling of the Current and Power Registers to whatever

values are most useful for a given application. One strategy may be to set the Calibration Register such that the

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

This approach would yield the highest resolution based using the previously calculated minimum current LSB in

the equation for the Calibration Register. 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 INA226 to cancel the total system error as shown in Equation 5.

(5)

16

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