Datasheet

INA226
www.ti.com SBOS547 –JUNE 2011
APPLICATION INFORMATION
The INA226 is a digital current shunt monitor with an I
2
C- and SMBus-compatible interface. It provides digital
current, voltage, and power readings necessary for accurate decision-making in precisely-controlled systems.
Programmable registers allow flexible configuration for measurement resolution as well as
continuous-versus-triggered operation. Detailed register information appears at the end of this data sheet,
beginning with Table 2. See the Register Block Diagram for a block diagram of the INA226.
INA226 TYPICAL APPLICATION
The front-page figure shows a typical application circuit for the INA226. Use a 0.1μF ceramic capacitor for
power-supply bypassing, placed as closely as possible to the supply and ground pins.
BASIC ADC FUNCTIONS
The INA226 performs two measurements on the power-supply bus of interest. The voltage developed from the
load current that flows through a shunt resistor creates a shunt voltage that is measured at the VIN+ and VIN–
pins. The device can also measure the power supply bus voltage by connecting this voltage to the V
BUS
pin. The
differential shunt voltage is measured with respect to the VIN– pin while the bus voltage is measured with
respect to ground.
The INA226 is typically powered by a separate supply that can range from 2.7V to 5.5V. The bus that is being
monitored can range in voltage from 0V to 36V. It is important to note here that based on the fixed 1.25mV LSB
for the bus voltage register that a full-scale register would result in a 40.96V value. The actual voltage that is
applied to the input pins of the INA226 should not exceed 36V. There are no special considerations for
power-supply sequencing because the common-mode input range and power-supply voltage are independent of
each other; therefore, the bus voltage can be present with the supply voltage off, and vice-versa.
As noted, the INA226 takes two measurements, shunt voltage and bus voltage. It then converts these
measurements to current, based on the Calibration Register value, and then calculates power. Refer to the
Configure/Measure/Calculate Example section for additional information on programming the Calibration
Register.
The INA226 has two operating modes, continuous and triggered, that determine how the ADC operates following
these conversions. When the INA226 is in the normal operating mode (that is, MODE bits of the Configuration
Register are set to '111'), it continuously converts a shunt voltage reading followed by a bus voltage reading.
After the shunt voltage reading, the current value is calculated (based on Equation 3). This current value is then
used to calculate the power result (using Equation 4). These values are subsequently stored in an accumulator,
and the measurement/calculation sequence repeats until the number of averages set in the Configuration
Register is reached. Following every sequence, the present set of values measured and calculated are
appended to previously collected values. Once all of the averaging has been completed, the final values for
shunt voltage, bus voltage, current, and power are updated in the corresponding registers that can then be read.
These values remain in the data output registers until they are replaced by the next fully completed conversion
results. Reading the data output registers does not affect a conversion in progress.
The Mode control in the Configuration Register also permits selecting modes to convert only the shunt voltage or
the bus voltage in order to further allow the user to configure the monitoring function to fit the specific application
requirements.
All current and power calculations are performed in the background and do not contribute to conversion time.
In triggered mode, writing any of the triggered convert modes into the Configuration Register (that is, MODE bits
of the Configuration Register are set to ‘001’, ‘010’, or ‘011’) triggers a single-shot conversion. This action
produces a single set of measurements; thus, to trigger another single-shot conversion, the Configuration
Register must be written to a second time, even if the mode does not change.
In addition to the two operating modes (continuous and triggered), the INA226 also has a power-down mode that
reduces the quiescent current and turns off current into the INA226 inputs, reducing the impact of supply drain
when the device is not being used. Full recovery from power-down mode requires 40ms. The registers of the
INA226 can be written to and read from while the device is in power-down mode. The device remains in
power-down mode until one of the active modes settings are written into the Configuration Register.
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Product Folder Link(s): INA226