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INA212 Datasheet(PDF) 9 Page - Texas Instruments |
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INA212 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 33 page INA226 www.ti.com SBOS547 – JUNE 2011 APPLICATION INFORMATION The INA226 is a digital current shunt monitor with an I2C- 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 0.1 μF 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 VBUS 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. Copyright © 2011, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Link(s): INA226 |
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