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INA128U-2K5 Datasheet(PDF) 10 Page - Texas Instruments |
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INA128U-2K5 Datasheet(HTML) 10 Page - Texas Instruments |
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10 / 20 page  INA128 INA129 SBOS051B − OCTOBER 1995 − REVISED FEBRUARY 2005 www.ti.com 10 OFFSET TRIMMING The INA128/INA129 is laser trimmed for low offset voltage and offset voltage drift. Most applications require no external offset adjustment. Figure 2 shows an optional circuit for trimming the output offset voltage. The voltage applied to Ref terminal is summed with the output. The op amp buffer provides low impedance at the Ref terminal to preserve good common-mode rejection. 10k Ω OPA177 100 Ω 100 Ω 1/2 REF200 1/2 REF200 V+ R G INA128 Ref V O V IN V IN + − ±10mV Adjustment Range V− 100 µA 100 µA Figure 2. Optional Trimming of Output Offset Voltage INPUT BIAS CURRENT RETURN PATH The input impedance of the INA128/INA129 is extremely high—approximately 1010 Ω. However, a path must be provided for the input bias current of both inputs. This input bias current is approximately ±2nA. High input impedance means that this input bias current changes very little with varying input voltage. Input circuitry must provide a path for this input bias current for proper operation. Figure 3 shows various provisions for an input bias current path. Without a bias current path, the inputs will float to a potential which exceeds the common-mode range, and the input amplifiers will saturate. If the differential source resistance is low, the bias current return path can be connected to one input (see the thermocouple example in Figure 3). With higher source impedance, using two equal resistors provides a balanced input with possible advantages of lower input offset voltage due to bias current and better high-frequency common-mode rejection. 47k Ω 47k Ω 10k Ω Microphone, Hydrophone etc. Thermocouple Center−tap provides bias current return. INA128 INA128 INA128 Figure 3. Providing an Input Common-Mode Current Path INPUT COMMON-MODE RANGE The linear input voltage range of the input circuitry of the INA128/INA129 is from approximately 1.4V below the positive supply voltage to 1.7V above the negative supply. As a differential input voltage causes the output voltage increase, however, the linear input range will be limited by the output voltage swing of amplifiers A1 and A2. So the linear common-mode input range is related to the output voltage of the complete amplifier. This behavior also depends on supply voltage—see performance curves, Input Common-Mode Range vs Output Voltage. Input-overload can produce an output voltage that appears normal. For example, if an input overload condition drives both input amplifiers to their positive output swing limit, the difference voltage measured by the output amplifier will be near zero. The output of A3 will be near 0V even though both inputs are overloaded. LOW VOLTAGE OPERATION The INA128/INA129 can be operated on power supplies as low as ±2.25V. Performance remains excellent with power supplies ranging from ±2.25V to ±18V. Most parameters vary only slightly throughout this supply voltage range—see typical performance curves. |
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Similar Description - INA128U-2K5 |
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