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INA199B3 Datasheet(PDF) 10 Page - Texas Instruments |
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INA199B3 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 28 page R SHUNT V REF V OUT V+ V CM R < 10W S R INT R < 10 S W R INT Load C F Bias INA199A1, INA199B1 INA199A2, INA199B2 INA199A3, INA199B3 SBOS469D – MAY 2009 – REVISED NOVEMBER 2012 www.ti.com UNIDIRECTIONAL OPERATION Unidirectional operation allows the INA199 to measure currents through a resistive shunt in one direction. The most frequent case of unidirectional operation sets the output at ground by connecting the REF pin to ground. In unidirectional applications where the highest possible accuracy is desirable at very low inputs, bias the REF pin to a convenient value above 50mV to get the device output swing into the linear range for zero inputs. A less frequent case of unipolar output biasing is to bias the output by connecting the REF pin to the supply; in this case, the quiescent output for zero input is at quiescent supply. This configuration would only respond to negative currents (inverted voltage polarity at the device input). BIDIRECTIONAL OPERATION Bidirectional operation allows the INA199 to measure currents through a resistive shunt in two directions. In this case, the output can be set anywhere within the limits of what the reference inputs allow (that is, between 0V to V+). Typically, it is set at half-scale for equal range in both directions. In some cases, however, it is set at a voltage other than half-scale when the bidirectional current is nonsymmetrical. The quiescent output voltage is set by applying voltage to the reference input. Under zero differential input conditions the output assumes the same voltage that is applied to the reference input. INPUT FILTERING An obvious and straightforward filtering location is at the device output. However, this location negates the advantage of the low output impedance of the internal buffer. The only other filtering option is at the device input pins. This location, though, does require consideration of the ±30% tolerance of the internal resistances. Figure 21 shows a filter placed at the inputs pins. Figure 21. Filter at Input Pins The addition of external series resistance, however, creates an additional error in the measurement so the value of these series resistors should be kept to 10 Ω or less if possible to reduce impact to accuracy. The internal bias network shown in Figure 21 present at the input pins creates a mismatch in input bias currents when a differential voltage is applied between the input pins. If additional external series filter resistors are added to the circuit, the mismatch in bias currents results in a mismatch of voltage drops across the filter resistors. This mismatch creates a differential error voltage that subtracts from the voltage developed at the shunt resistor. This error results in a voltage at the device input pins that is different than the voltage developed across the shunt resistor. Without the additional series resistance, the mismatch in input bias currents has little effect on device operation. The amount of error these external filter resistor add to the measurement can be calculated using Equation 2 where the gain error factor is calculated using Equation 1. 10 Submit Documentation Feedback Copyright © 2009–2012, Texas Instruments Incorporated Product Folder Links: INA199A1 INA199B1 INA199A2 INA199B2 INA199A3 INA199B3 |
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