Datasheet

´
Power Register
Current Register
I C
2
Interface
Voltage Register
GND
V
BUS
ADC
V
I
A0
Alert
A1
SDA
SCL
C
0.1 F
BYPASS
m
10A
Load
Alert Register
V
(Supply Voltage)
S
+12V Supply
V
IN-
V
IN+
R
2m
SHUNT
W
ShuntVoltage CalibrationRegister
2048
·
Current =
INA226
www.ti.com SBOS547 –JUNE 2011
CONFIGURE/MEASURE/CALCULATE EXAMPLE
In this example, shown in Figure 23, a nominal 10A load creates a differential voltage of 20mV across a 2mΩ
shunt resistor. The bus voltage for the INA226 is measured at the external V
BUS
input pin, which in this example
is connected to the VIN– pin to measure the voltage level delivered to the load. For this example, the V
BUS
pin
measures less than 12V because the voltage at the VIN– pin is 11.98V 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 15A, the Current_LSB is calculated to be
457.7μA/bit using Equation 2. Using a value for the Current_LSB of 500μA/Bit or 1mA/Bit would significantly
simplifiy the conversion from the Current Register and Power Register to amps and watts. For this example, a
value of 1mA/bit was chosen for the current LSB. Using this value for the Current_LSB does trade a small
amount of resolution for having a simpler conversion process on the user side. Using Equation 1 in this example
with a current LSB of 1mA/bit and a shunt resistor of 2mΩ 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 1mA/bit results in the original 10A level stated in the example.
(3)
The LSB for the Bus Voltage Register (02h) is a fixed 1.25mV/bit, which means that the 11.98V present at the
V
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 V
BUS
pin is only able to measure positive voltages.
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Product Folder Link(s): INA226