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INA139-Q1 Datasheet(PDF) 7 Page - Texas Instruments |
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INA139-Q1 Datasheet(HTML) 7 Page - Texas Instruments |
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7 / 16 page  2 1 p 2 1 INA139-Q1 INA169-Q1 www.ti.com SGLS185E – SEPTEMBER 2003 – REVISED MAY 2011 POWER SUPPLIES The input circuitry of the INA139 can accurately measure beyond its power-supply voltage, V+. For example, the V+ power supply can be 5 V, whereas the load power supply voltage is up to 36 V (or 60 V with the INA169). However, the output voltage range of the OUT terminal is limited by the lesser of the two voltages (see the Output Voltage Range section). SELECTING RS AND RL The value chosen for the shunt resistor, RS, depends on the application and is a compromise between small-signal accuracy and maximum permissible voltage loss in the measurement line. High values of RS provide better accuracy at lower currents by minimizing the effects of offset, while low values of RS minimize voltage loss in the supply line. For most applications, best performance is attained with an RS value that provides a full-scale shunt voltage range of 50 mV to 100 mV. Maximum input voltage for accurate measurements is 500 mV. RL is chosen to provide the desired full-scale output voltage. The output impedance of the INA139 OUT terminal is very high, which permits using values of RL up to 100 kΩ with excellent accuracy. The input impedance of any additional circuitry at the output should be much higher than the value of RL to avoid degrading accuracy. Some analog-to-digital (A/D) converters have input impedances that significantly affect measurement gain. The input impedance of the A/D converter can be included as part of the effective RL if its input can be modeled as a resistor to ground. Alternatively, an op amp can be used to buffer the A/D converter input as shown in Figure 10. See Figure 9 for recommended values of RL. OUTPUT VOLTAGE RANGE The output of the INA139 is a current, which is converted to a voltage by the load resistor, RL. The output current remains accurate within the compliance voltage range of the output circuitry. The shunt voltage and the input common-mode and power-supply voltages limit the maximum possible output swing. The maximum output voltage compliance is limited by the lower of the two equations below: VOUT MAX = (V+) − 0.7 V − (VIN+ − VIN−) or VOUT MAX = VIN− − 0.5 V (whichever is lower) BANDWIDTH Measurement bandwidth is affected by the value of the load resistor, RL. High gain produced by high values of RL yields a narrower measurement bandwidth (see the Typical Characteristics section). For widest possible bandwidth, keep the capacitive load on the output to a minimum. If bandwidth limiting (filtering) is desired, a capacitor can be added to the output (as shown in Figure 11), which will not cause instability. Figure 10. Buffering Output to Drive the A/D Figure 11. Output Filter Converter Copyright © 2003–2011, Texas Instruments Incorporated 7 |
Similar Part No. - INA139-Q1_15 |
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Similar Description - INA139-Q1_15 |
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