Datasheet
MaxPossible_I=
V
R
SHUNT_MAX
SHUNT
MaxPossible_I=320
Minimum_LSB=
Max_Expected_I
32767
Minimum_LSB=1.831 10´
-3
Maximum_LSB=
Max_Expected_I
4096
Maximum_LSB=14.652 10´
-3
Cal=trunc
0.04096
Current_LSB R´
SHUNT
Cal=21557
Power_LSB=20 Current_LSB´
Power_LSB=38 10´
-3
TPS2480
TPS2481
www.ti.com
SLUS939B –APRIL 2010–REVISED DECEMBER 2010
Calibration Example 2 (Overflow Possible)
This design example uses the nine-step procedure for calibrating the TPS2480/81 where overflow is possible.
Figure 27 illustrates how the same procedure is performed using the automated TPS2480/81EVM software.
NOTE
(The same numbers used in the nine-step example are used in the software example in
Figure 27. Also note that Figure 27 illustrates which results correspond to which step (for
example, the information entered in Step 1 is circled in Figure 27 and labeled).
1. Establish the following parameters:
V
BUS_MAX
= 32, This does not mean the input can go over 26 V!
V
SHUNT_MAX
= 0.32
R
SHUNT
= 0.001
2. Determine the maximum possible current using Equation 39:
(39)
3. Choose the desired maximum current value: Max_Expected_I, ≤ MaxPossible_I. This value is selected
based on system expectations.
Max_Expected_I = 60
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.
(40)
(41)
Choose an LSB in the range: Minimum_LSB<Selected_LSB<Maximum_LSB
Current_LSB = 1.9 × 10
–3
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 42:
(42)
6. Calculate the Power LSB using Equation 43. Equation 43 shows a general formula; because the bus voltage
measurement LSB is always 4mV, the power formula reduces to calculate the result.
(43)
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