MaxPossible_I=

V

R

SHUNT_MAX

SHUNT

MaxPossible_I=0.64

Minimum_LSB=

Max_Expected_I

32767

Minimum_LSB=18.311

10

´

-6

Maximum_LSB=

Max_Expected_I

4096

Maximum_LSB=146.520

10

´

-6

Cal=trunc

0.04096

Current_LSB

R

´

SHUNT

Cal=4096

INA220

SBOS459D – JUNE 2009 – REVISED SEPTEMBER 2010

www.ti.com

PROGRAMMING THE INA220 POWER

Calibration Register can also be selected to provide

MEASUREMENT ENGINE

values in the Current and Power Registers that either

provide direct decimal equivalents of the values being

Calibration Register and Scaling

measured, or yield a round LSB number. After these

choices have been made, the Calibration Register

The Calibration Register makes it possible to set the

also offers possibilities for end user system-level

scaling of the Current and Power Registers to

calibration, where the value is adjusted slightly to

whatever

values

are

most

useful

for

a

given

cancel total system error.

application.

One

strategy

may

be

to

set

the

Calibration Register such that the largest possible

Below are two examples for configuring the INA220

number is generated in the Current Register or Power

calibration.

Both

examples

are

written

so

the

Register

at

the

expected

full-scale

point;

this

information directly relates to the calibration setup

approach

yields

the

highest

resolution.

The

found in the INA220EVM software.

Calibration Example 1: Calibrating the INA220 with no possibility for overflow. (Note that the numbers

used in this example are the same used with the INA220EVM software as shown in Figure 20.)

1. Establish the following parameters:

2. Using Equation 1, determine the maximum possible current .

(1)

3. Choose the desired maximum current value. This value is selected based on system expectations.

Max_Expected_I = 0.6

4. Calculate the possible range of current LSBs. To calculate this range, first compute a range of LSBs that is

appropriate for the design. Next, select an LSB within this range. Note that the results will have the most

resolution when the minimum LSB is selected. Typically, an LSB is selected to be the nearest round number

to the minimum LSB value.

(2)

(3)

Choose an LSB in the range: Minimum_LSB<Selected_LSB < Maximum_LSB

Note:

This value was selected to be a round number near the Minimum_LSB. This selection allows for

good resolution with a rounded LSB.

5. Compute the Calibration Register value using Equation 4:

(4)

16

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