INA230_13 Datasheet, PDF (10/35 Pages) Texas Instruments – High- or Low-Side Measurement, Bidirectional CURRENT/POWER MONITOR with I2C Interface

INA230
SBOS601 – FEBRUARY 2012
www.ti.com
APPLICATION INFORMATION
The INA230 is a digital current shunt monitor with an I²C- and SMBus-compatible interface. This device 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 towards the end of this data sheet,
beginning with Table 2. See Figure 1 for a block diagram of the INA230.
INA230 TYPICAL APPLICATION
The figure on the front page shows a typical application circuit for the INA230. For power-supply bypassing, use
a 0.1-μF ceramic capacitor placed as close as possible to the supply and ground pins.
BASIC ANALOG-TO_DIGITAL CONVERTER (ADC) FUNCTIONS
The INA230 performs two measurements on the power-supply bus of interest. The voltage developed from the
load current that flows through a shunt resistor creates the shunt voltage signal that is measured at the IN+ and
IN– pins. The device can also measure the power supply bus voltage by connecting this voltage to the BUS pin.
The differential shunt voltage is measured with respect to the IN– pin while the bus voltage is measured with
respect to ground.
The INA230 is typically powered by a separate supply that can range from 2.7 V to 5.5 V. The bus that is being
monitored can range in voltage from 0 V to 28 V. NOTE: Based on the fixed 1.25 mV LSB for the bus voltage
register, a full-scale register would result in a 40.96-V value. However, the actual voltage that is applied
to the input pins of the INA230 should not exceed 28 V. 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 INA230 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 INA230 has two operating modes, continuous and triggered, that determine how the ADC operates after
these conversions. When the INA230 is in the normal operating mode (that is, the 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. Note that the current and power calculations are based on the value
programmed into the Calibration register. If the Calibration register is not programmed, the result of the current
and power calculations is zero. Following every sequence, the present set of measured and calculated values
are appended to the previously collected values. After all of the averaging has been completed, the final values
for shunt voltage, bus voltage, current, and power are updated in the corresponding registers and 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 bits in the Configuration register also permit selecting specific modes to convert only the shunt
voltage or the bus voltage in order to further allow the monitoring function configuration to fit 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, the 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. To trigger another single-shot conversion, the Configuration register
must be written to again, even if the mode does not change.
In addition to the two operating modes (continuous and triggered), the INA230 also has a power-down mode that
reduces the quiescent current and turns off current into the INA230 inputs, which reduces the impact of supply
drain when the device is not being used. Full recovery from power-down mode requires 40 ms. The registers of
the INA230 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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