Datasheet

Power_LSB=20Current_LSB
Power_LSB=400 10´
-6
(5)
Max_Current=Current_LSB 32767´
Max_Current=0.65534
(6)
Max_ShuntVoltage=Max_Current_Before_Overflow R´
SHUNT
Max_ShuntVoltage=0.32
(7)
MaximumPower=Max_Current_Before_Overflow V´
BUS_MAX
MaximumPower=20.48
(8)
Corrected_Full_Scale_Cal=trunc
Cal MeasShuntCurrent
INA209_Current
´
Corrected_Full_Scale_Cal=3548
(9)
INA209
SBOS403B – JUNE 2007 – REVISED MARCH 2009 ......................................................................................................................................................... www.ti.com
6. Calculate the Power LSB, using Equation 5 . Equation 5 shows a general formula; because the bus voltage
measurement LSB is always 4mV, the power formula reduces to the calculated result.
7. Compute the maximum current and shunt voltage values (before overflow), as shown by Equation 6 and
Equation 7 . Note that both Equation 6 and Equation 7 involve an If - then condition:
If Max_Current ≥ Max Possible_I then
Max_Current_Before_Overflow = MaxPossible_I
Else
Max_Current_Before_Overflow = Max_Current
End If
(Note that Max_Current is greater than MaxPossible_I in this example.)
Max_Current_Before_Overflow = 0.64 (Note: This result is displayed by software as seen in Figure 25 .)
If Max_ShuntVoltage ≥ V
SHUNT_MAX
Max_ShuntVoltage_Before_Overflow = V
SHUNT_MAX
Else
Max_ShuntVoltage_Before_Overflow= Max_ShuntVoltage
End If
(Note that Max_ShuntVoltage is greater than V
SHUNT_MAX
in this example.)
Max_ShuntVoltage_Before_Overflow = 0.32 (Note: This result is displayed by software as seen in
Figure 25 .)
8. Compute the maximum power with Equation 8 .
9. (Optional second Calibration step.) Compute corrected full-scale calibration value based on measured
current.
INA209_Current = 0.63484
MeaShuntCurrent = 0.55
Figure 25 illustrates how to perform the same procedure discussed in this example using the automated
INA209EVM software. Note that the same numbers used in the nine-step example are used in the software
example in Figure 25 . Also note that Figure 25 illustrates which results correspond to which step (for example,
the information entered in Step 1 is enclosed in a box in Figure 25 and labeled).
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