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INA122PG4 Datasheet(PDF) 9 Page - Burr-Brown (TI) |
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INA122PG4 Datasheet(HTML) 9 Page - Burr-Brown (TI) |
9 / 14 page 9 ® INA122 equal to 0V. The outputs of both A1 and A2 must be 0V. But any small positive voltage applied to V IN + requires that A 2’s output must swing below 0V, which is clearly impossible without a negative power supply. To achieve common-mode range that extends to single- supply ground, the INA122 uses precision level-shifting buffers on its inputs. This shifts both inputs by approxi- mately +0.5V, and through the feedback network, shifts A2’s output by approximately +0.6V. With both inputs and VREF at single-supply, A2’s output is well within its linear range. A positive VIN+ causes A2’s output to swing below 0.6V. As a result of this input level-shifting, the voltages at pin 1 and pin 8 are not equal to their respective input terminal voltages (pins 2 and 3). For most applications, this is not important since only the gain-setting resistor connects to these pins. LOW VOLTAGE OPERATION The INA122 can be operated on a single power supply as low as +2.2V (or a total of +2.2V on dual supplies). Perfor- mance remains excellent throughout the power supply range up to +36V (or ±18V). Most parameters vary only slightly throughout this supply voltage range—see typical perfor- mance curves. Operation at very low supply voltage requires careful atten- tion to ensure that the common-mode voltage remains within its linear range. LOW QUIESCENT CURRENT OPERATION The INA122 maintains its low quiescent current (60 µA) while the output is within linear operation (up to 200mV from the supply rails). When the input creates a condition that overdrives the output into saturation, quiescent current increases. With VO overdriven into the positive rail, the quiescent current increases to approximately 400 µA. Like- wise, with VO overdriven into the negative rail (single supply ground) the quiescent current increases to approxi- mately 200 µA. OUTPUT CURRENT RANGE Output sourcing and sinking current values versus the output voltage ranges are shown in the typical performance curves. The positive and negative current limits are not equal. Positive output current sourcing will drive moderate to high load impedances. Battery operation normally requires the careful management of power consumption to keep load impedances very high throughout the design. FIGURE 6. Single-Supply Current Shunt Measurement. INA122 ADS7816 12-Bit A/D V IN R G R S 0.02 Ω I L 2.5A + V IN – 3 2 4 5 6 7 G = 100 1 8 +5V V+ Differential measurement avoids ground loop errors. Load Shunt 7 5 6 8 4 2 1 3 Chip Select Clock Serial Data CS CLK D V REF +IN –IN 1k Ω 0.47µF 50mV FIGURE 5. Micropower Single Supply Bridge Amplifier. 1k Ω REF200 200µA INA122 3 8 7 4 5 6 2 1 V CM ≈ 100mV ≈ 200mV V IN + V IN R G V O = 0.1V to 4.9V V O – (60µA) Ref(1) +5V NOTE: (1) To accomodate bipolar input signals, V REF can be offset to a positive voltage. Output voltage is then referred to the voltage applied to Ref. |
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