MaxPossible_I=

V

R

SHUNT_MAX

SHUNT

MaxPossible_I=0.064

Minimum_LSB=

Max_Expected_I

32767

Minimum_LSB=1.831

10

´

-6

Maximum_LSB=

Max_Expected_I

4096

Maximum_LSB=14.652

10

´

-6

Cal=trunc

0.04096

Current_LSB

R

´

SHUNT

Cal=4311

Power_LSB=20Current_LSB

Power_LSB=38

10

´

-6

INA220

www.ti.com

SBOS459D – JUNE 2009 – REVISED SEPTEMBER 2010

Calibration Example 2 (Overflow Possible)

software. Note that the same numbers used in the

nine-step example are used in the software example

This design example uses the nine-step procedure for

in Figure 21. Also note that Figure 21 illustrates which

calibrating the INA220 where overflow is possible.

results correspond to which step (for example, the

Figure 21 illustrates how the same procedure is

information entered in Step 1 is circled in Figure 21

performed

using

the

automated

INA220EVM

and labeled).

1. Establish the following parameters:

2. Determine the maximum possible current using Equation 10:

(10)

3. Choose the desired maximum current value: Max_Expected_I,

≤ MaxPossible_I. This value is selected

based on system expectations.

Max_Expected_I = 0.06

4. Calculate the possible range of current LSBs. This calculation is done by first computing a range of LSB's

that is appropriate for the design. Next, select an LSB withing 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.

(11)

(12)

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 section allows for good

resolution with a rounded LSB.

5. Compute the calibration register using Equation 13:

(13)

6. Calculate the Power LSB using Equation 14. Equation 14 shows a general formula; because the bus voltage

measurement LSB is always 4mV, the power formula reduces to calculate the result.

(14)

Copyright © 2009–2010, Texas Instruments Incorporated

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