Datasheet

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=20Current_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:
V
BUS_MAX
= 32
V
SHUNT_MAX
= 0.32
R
SHUNT
= 5
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
Current_LSB = 1.9 × 10
–6
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)
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