Datasheet

R
2mW
SHUNT
10A
Load
+12V
VCM
GND
V
I
V
IN+
V
IN-
PowerRegister
I C
Interface
2
CurrentRegister
VoltageRegister
SDA
SCK
A0
A1
0.1 Fm10 Fm
+3.3Vto+5V
V (SupplyVoltage)
S
´
INA219
www.ti.com SBOS448F –AUGUST 2008– REVISED SEPTEMBER 2011
CONFIGURE/MEASURE/CALCULATE shunt voltage. By knowing the value of the shunt
EXAMPLE resistor, the device can then calculate the amount of
current that created the measured shunt voltage drop.
In this example, the 10A load creates a differential
The first step when calculating the calibration value is
voltage of 20mV across a 2mΩ shunt resistor. The
setting the current LSB. The Calibration Register
voltage present at the V
IN–
pin is equal to the
value is based on a calculation that has its precision
common-mode voltage minus the differential drop
capability limited by the size of the register and the
across the resistor. The bus voltage for the INA219 is
Current Register LSB. The device can measure
internally measured at the V
IN–
pin to measure the
bidirectional current; thus, the MSB of the Current
voltage level delivered to the load. For this example,
Register is a sign bit that allows for the rest of the 15
the voltage at the V
IN–
pin is 11.98V. For this
bits to be used for the Current Register value. It is
particular range (40mV full-scale), this small
common when using the current value calculations to
difference is not a significant deviation from the 12V
use a resolution between 12 bits and 15 bits.
common-mode voltage. However, at larger full-scale
Calculating the current LSB for each of these
ranges, this deviation can be much larger.
resolutions provides minimum and maximum values.
These values are calculated assuming the maximum
Note that the Bus Voltage Register bits are not
current that will be expected to flow through the
right-aligned. In order to compute the value of the
current shunt resistor, as shown in Equation 2 and
Bus Voltage Register contents using the LSB of 4mV,
Equation 3. To simplify the mathematics, it is
the register must be shifted right by three bits. This
common to choose a round number located between
shift puts the BD0 bit in the LSB position so that the
these two points. For this example, the maximum
contents can be multiplied by the 4mV LSB value to
current LSB is 3.66mA/bit and the minimum current
compute the bus voltage measured by the device.
LSB would be 457.78µA/bit assuming a maximum
The shifted value of the bus voltage register contents
expected current of 15A. For this example, a value of
is now equal to BB3h, a decimal equivalent of 2995.
1mA/bit was chosen for the current LSB. Setting the
This value of 2995 multiplied by the 4mV LSB results
current LSB to this value allows for sufficient
in a value of 11.98V.
precision while serving to simplify the math as well.
The Calibration Register (05h) is set in order to
Using Equation 4 results in a Calibration Register
provide the device information about the current
value of 20480, or 5000h.
shunt resistor that was used to create the measured
Figure 23. Example Circuit Configuration
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