PROGRAMMING THE INA220 POWER MEASUREMENT ENGINE

Calibration Register and Scaling

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

MaxPossible_I=

V

R

SHUNT_MAX

SHUNT

MaxPossible_I=0.64

(1)

Minimum_LSB=

Max_Expected_I

32767

Minimum_LSB=18.311

10

´

-6

(2)

Maximum_LSB=

Max_Expected_I

4096

Maximum_LSB=146.520

10

´

-6

(3)

Cal=trunc

0.04096

Current_LSB

R

´

SHUNT

Cal=4096

(4)

INA220

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 yields the highest resolution. 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 number. After these choices have been made, the Calibration Register also offers possibilities

for end user system-level calibration, where the value is adjusted slightly to cancel total system error.

Below are two examples for configuring the INA220 calibration. Both examples are written so the information

directly relates to the calibration setup found in the INA220EVM software.

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 .

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.

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:

16

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