The INA226 device 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 IN+ and IN– pins. The device can also measure the power supply bus voltage by connecting this voltage to the VBUS pin. The differential shunt voltage is measured with respect to the IN– pin while the bus voltage is measured with respect to ground.

The device 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 36 V. Based on the fixed 1.25-mV LSB for the Bus Voltage Register that a full-scale register results in a 40.96 V value.

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 reciprocally.

The device takes two measurements, shunt voltage and bus voltage. The device then converts these measurements to current, based on the Calibration Register value, and then calculates power. Refer to the Programming the Calibration Register section for additional information on programming the Calibration Register.

The device has two operating modes, continuous and triggered, that determine how the ADC operates following these conversions. When the device is in the normal operating mode (that is, MODE bits of the Configuration Register (00h) are set to '111'), the device 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 (00h) is reached. Following every sequence, the present set of values measured and calculated are appended to 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 that can then be read. These values remain in the data output registers until the values 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 Conversion Register (00h) also permits selecting modes to convert only the shunt voltage or the bus voltage 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 (00h) (that is, MODE bits of the Configuration Register (00h) 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 (00h) 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 device also has a power-down mode that reduces the quiescent current and turns off current into the device inputs, reducing the impact of supply drain when the device is not being used. Full recovery from power-down mode requires 40µs. The registers of the device 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 (00h).

Although the device can be read at any time, and the data from the last conversion remain available, the Conversion Ready flag bit (Mask/Enable Register, CVRF bit) is provided to help coordinate one-shot or triggered conversions. The Conversion Ready flag (CVRF) bit is set after all conversions, averaging, and multiplication operations are complete.

The Conversion Ready flag (CVRF) bit clears under these conditions:

• Writing to the Configuration Register (00h), except when configuring the MODE bits for power-down mode; or
• Reading the Mask/Enable Register (06h)