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AD627B bảng dữ liệu(PDF) 11 Page - Analog Devices |
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AD627B bảng dữ liệu(HTML) 11 Page - Analog Devices |
11 / 16 page AD627 –11– REV. A Table I. Recommended Values of Gain Resistors Desired 1% Std Table Resulting Gain Value of RG, Gain 5 ∞ 5 6 200 k 6 7 100 k 7 8 68.1 k 7.93 9 51.1 k 8.91 10 40.2 k 9.98 15 20 k 15 20 13.7 k 19.6 25 10 k 25 30 8.06 k 29.81 40 5.76 k 39.72 50 4.53 k 49.15 60 3.65 k 59.79 70 3.09 k 69.73 80 2.67 k 79.9 90 2.37 k 89.39 100 2.1 k 99.24 200 1.05 k 195.48 500 412 489.44 1000 205 980.61 Reference Terminal The reference terminal potential defines the zero output voltage and is especially useful when the load does not share a precise ground with the rest of the system. It provides a direct means of injecting a precise offset to the output. The reference terminal is also useful when bipolar signals are being amplified as it can be used to provide a virtual ground voltage. Since the AD627 output voltage is developed with respect to the potential on the reference terminal, it can solve many grounding problems by simply tying the REF pin to the appropriate “local ground.” The REF pin should however be tied to a low imped- ance point for optimal CMR. Input Range Limitations in Single Supply Applications In general, the maximum achievable gain is determined by the available output signal range. However, in single supply applica- tions where the input common mode voltage is close to or equal to zero, some limitations on the gain can be set. While the In- put, Output and Reference Pins have ranges that are nominally defined on the specification pages, there is a mutual interdepen- dence between the voltage ranges on these pins. Figure 34 shows the simplified schematic of the AD627, driven by a differential voltage VDIFF which has a common mode component, VCM. The voltage on the output of op amp A1 is a function of VDIFF, VCM, the voltage on the REF pin and the programmed gain. This voltage is given by the equation: VA1 = 1.25 (VCM + 0.5 V) – 0.25 VREF – VDIFF (25 k Ω/R G – 0.625) We can also express the voltage on A1 as a function of the ac- tual voltages on the –IN and +IN pins (V– and V+) VA1 = 1.25 (V– + 0.5 V) – 0.25 VREF – (V+ – V–) 25 k Ω/R G A1’s output is capable of swinging to within 50 mV of the nega- tive rail and to within 200 mV of the positive rail. From either of the above equations, it is clear that an increasing VREF, (while it acts as a positive offset at the output of the AD627), tends to decrease the voltage on A1. Figures 35 and 36 show the maxi- mum voltages that can be applied to the REF pin, for a gain of five for both the single and dual supply cases. Raising the input common-mode voltage will increase the voltage on the output of A1. However, in single supply applications where the common- mode voltage is low, a differential input voltage or a voltage on REF that is too high can drive the output of A1 into the ground rail. Some low side headroom is added by virtue of both inputs being shifted upwards by about 0.5 V (i.e., by the VBE of Q1 and Q2). The above equations can be used to check that the voltage on amplifier A1 is within its operating range. Table II gives values for the maximum gains for various single supply input conditions. The resulting output swings shown refer to 0 V. The voltages on the REF pins has been set to either A1 200k –VS OUTPUT +VS –VS 2k +IN Q2 +VS –VS Q1 2k –IN 100k REF EXTERNAL GAIN RESISTOR 100k 25k 25k RG 200k –IN VA +IN VCM V+ V– VDIFF 2 VDIFF 2 A2 Figure 34. Amplifying Differential Signals with a Common-Mode Component Table II. Maximum Gain for Low Common-Mode Single Supply Applications REF Supply RG (1% Resulting Output Swing VIN Pin Voltage Tolerance) Max Gain WRT 0 V ±100 mV, V CM = 0 V 2 V +5 V to +15 V 28.7 k Ω 12.0 0.8 V to 3.2 V ±50 mV, V CM = 0 V 2 V +5 V to +15 V 10.7 k Ω 23.7 0.8 V to 3.2 V ±10 mV, V CM = 0 V 2 V +5 V to +15 V 1.74 k Ω 119.9 0.8 V to 3.2 V V– = 0 V, V+ = 0 V to 1 V 1 V +10 V to +15 V 78.7 k Ω 7.5 1 V to 8.5 V V– = 0 V, V+ = 0 mV to 100 mV 1 V +5 V to +15 V 7.87 k Ω 31 1 V to 4.1 V V– = 0 V, V+ = 0 mV to 10 mV 1 V +5 V to +15 V 7.87 Ω 259.1 1 V to 3.6 V |
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Mô tả tương tự - AD627B |
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