Datasheet

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:
V
BUS_MAX
= 32
V
SHUNT_MAX
= 0.32
R
SHUNT
= 0.5
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
Current_LSB = 20 × 10
–6
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)
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