Datasheet

´
Power Register
Current Register
I C
2
Interface
Voltage Register
GND
BUS
ADC
V
I
A0
ALERT
A1
SDA
SCL
C
0.1 F
BYPASS
m
10A
Load
Alert Register
V
(Supply Voltage)
S
+12-V Supply
IN-
IN+
R
2 m
SHUNT
W
ShuntVoltage CalibrationRegister
2048
·
Current =
INA230
SBOS601 –FEBRUARY 2012 www.ti.com
CONFIGURE/MEASURE/CALCULATE EXAMPLE
In this example, shown in Figure 23, a nominal 10-A load creates a differential voltage of 20 mV across a 2-mΩ
shunt resistor. The bus voltage for the INA230 is measured at the external BUS input pin; in this example, BUS
is connected to the IN– pin to measure the voltage level delivered to the load. For this example, the BUS pin
measures less than 12 V because the voltage at the IN– pin is 11.98 V as a result of the voltage drop across the
shunt resistor.
Figure 23. Example Circuit Configuration
For this example, assuming a maximum expected current of 15 A, the Current_LSB is calculated to be 457.7
μA/bit using Equation 2. Using a value of 500 μA/bit or 1 mA/bit for the Current_LSB significantly simplifies the
conversion from the Current register and Power register to amps and watts. For this example, a value of 1 mA/bit
was chosen for the Current register LSB. Using this value for the Current_LSB trades a small amount of
resolution for a simpler conversion process on the processor side. Using Equation 1 in this example with a
current LSB of 1 mA/bit and a shunt resistor of 2 mΩ results in a Calibration register value of 2560, or A00h.
The Current register (04h) is then calculated by multiplying the decimal value of the Shunt Voltage register
contents by the decimal value of the Calibration register and then dividing by 2048, as shown in Equation 3. For
this example, the Shunt Voltage register contains a value of 8,000, which is multiplied by the Calibration register
value of 2560 and then divided by 2048 to yield a decimal value for the Current register of 10000, or 2710h.
Multiplying this value by 1 mA/bit results in the original 10-A level stated in the example.
(3)
The LSB for the Bus Voltage register (02h) is a fixed 1.25 mV/bit. This fixed value means that the 11.98V present
at the BUS pin results in a register value of 2570h, or a decimal equivalent of 9584. Note that the MSB of the
Bus Voltage register is always zero because the BUS pin is only able to measure positive voltages.
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