Datasheet

Current BusVoltage
20,000
·
Power =
Corrected_Full_Scale_Cal = trunc
Cal MeasShuntCurrent
INA230_Current
´
INA230
www.ti.com SBOS601 –FEBRUARY 2012
The Power register (03h) is then calculated by multiplying the decimal value of the Current register, 10000, by
the decimal value of the Bus Voltage register, 9584, and then dividing by 20,000, as defined in Equation 4. For
this example, the result for the Power register is 12B8h, or a decimal equivalent of 4792. Multiplying this result by
the power LSB (25 times the [1 × 10
–3
Current_LSB]) results in a power calculation of (4792 × 25 mW/bit), or
119.8 W. The Power register LSB has a fixed ratio to the Current register LSB of 25 W/bit to 1 A/bit. For this
example, a programmed Current register LSB of 1 mA/bit results in a Power register LSB of 25 mW/bit. This ratio
is internally programmed to ensure that the scaling of the power calculation is within an acceptable range. A
manual calculation for the power being delivered to the load would use a bus voltage of 11.98 V (12V
CM
– 20 mV
shunt drop) multiplied by the load current of 10 A to give a result of 119.8 W.
(4)
Table 1 shows the steps for configuring, measuring, and calculating the values for current and power for this
device.
Table 1. Configure/Measure/Calculate Example
(1)
STEP # REGISTER NAME ADDRESS CONTENTS DEC LSB VALUE
Step 1 Configuration 00h 4127h — — —
Step 2 Shunt 01h 1F40h 8000 2.5 µV 20m V
Step 3 Bus 02h 2570h 9584 1.25 mV 11.98 V
Step 4 Calibration 05h A00h 2560 — —
Step 5 Current 04h 2710 10000 1 mA 10 A
Step 6 Power 03h 12B8h 4792 25 mW 119.8 W
(1) Conditions: Load = 10 A, V
CM
= 12 V, R
SHUNT
= 2 mΩ, and V
BUS
=11.98 V.
PROGRAMMING THE INA230 POWER MEASUREMENT ENGINE
Calibration Register and Scaling
The Calibration register makes it possible to set the scaling of the Current and Power registers to the values that
are most useful for a given application. One strategy may be to set the Calibration register so that the largest
possible number is generated in the Current register or Power register at the expected full-scale point. This
approach yields the highest resolution based on the previously calculated minimum Current_LSB in the equation
for the Calibration register (Equation 1). The Calibration register can also be selected to provide values in the
Current and Power registers that either provide direct decimal equivalents of the values being measured, or yield
a round LSB value for each corresponding register. After these choices have been made, the Calibration register
also offers possibilities for end-user, system-level calibration. By physically measuring the current with an
external ammeter, the exact current is known. The value of the Calibration register can then be adjusted based
on the measured current result of the INA230 to cancel the total system error, as shown in Equation 5.
(5)
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