Datenblatt-Suchmaschine für elektronische Bauteile |
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AD22050 Datenblatt(PDF) 8 Page - Analog Devices |
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AD22050 Datenblatt(HTML) 8 Page - Analog Devices |
8 / 8 page AD22050 –8– REV. C A unique method of feedback around A1, provided by R9 and R7, sets the closed-loop gain of the preamplifier to ×10 (from the input pins). The feedback network is balanced by the inclu- sion of R6 and R8. The small value of R7 results in a more practical value for R9 (which would have to be 2 M Ω if the feedback were taken directly to the inputs of A1). R8 is not directly connected to ground, but to an optional voltage of one half that is applied to Pin 7 (OFS). It is trimmed to within close tolerances through R10 and R11. This allows the output of A1 to be offset to midscale, typically +VS/2, by tying Pins 6 and 7 together. (For an example of the use of this feature, see Figure 12.) The gain is adjusted by the single resistor R5, which acts only on the differential signal. More importantly, it also results in much less feed forward of the common-mode signal to the output of A1, which, being a single-supply circuit, has no means of pulling this output down toward ground in those circumstances where the common-mode input is very positive while the net differential signal is small. (The output of A1 is the collector of a PNP transistor whose emitter is tied to +VS.) R16 is specifically included to alleviate this problem. The output of the preamplifier is connected to Pin 3 via R12, a 100 k Ω resistor that is trimmed to within ±3%. The inclusion of R12 allows a low-pass filter to be formed, with an accurate time constant, by placing a capacitor from Pin 3 to ground. By separating the connections at Pins 3 and 4, a two-pole Sallen and Key filter can be formed (see Low-Pass Filtering section) and also provides a means for setting the overall gain to values other than ×20 (see Altering the Gain section). The output buffer has a gain of ×2, set by the feedback network around op amp A2, formed by R15 and R13 R14. Note that this gain is not trimmed to a precise value, but may have a tolerance of ±3% (max). Only the overall gain of A1 and A2 is trimmed to within ±0.5% by R5. As a consequence, the gain of A1 may be in error by ±3% (max) as the trim to R5 absorbs the initial error in the gain of A2. In most applications Pins 3 and 4 are simply tied together, but the output buffer can be used independently if desired. The offset voltage of A2 is nulled during manufacture. R17 is included to minimize the offset due to bias currents. It is recommended, in applications where A2 is used independently and the source resistance is less than 100 k Ω, that the necessary extra resistance should be included. The output of A2 is the collector of a PNP transistor whose emitter is tied to +VS. The bias current out of the inverting input of this amplifier generates an offset voltage of about +1 mV in R13 R14, which is passed directly to the output via R15. This sets the lowest output that can be reached when there is no load resistor. However, the output can drive a 1 k Ω load to at least +4.5 V when +VS = +5 V. If operation to much lower minimum voltages is essential, a load resistor can be added externally. AD22050 A1 A2 +VS R12 100k A2 C1 5pF R1 200k R18 1k A1 R19 1k C2 5pF R4 41k R9 10k R7 250 R17 95k R15 10k OUT R16 10k R14 20k R13 20k R5 2.6k R3 41k GND OFS R6 250k R8 9k R2 200k R11 2k R10 2k IN+ IN– Figure 16. Simplified Schematic of AD22050, Including Component Values OUTLINE DIMENSIONS Dimensions shown in inches and (mm). Plastic SOIC Package (SO-8) 0.1968 (5.00) 0.1890 (4.80) 8 5 4 1 0.2440 (6.20) 0.2284 (5.80) PIN 1 0.1574 (4.00) 0.1497 (3.80) 0.0688 (1.75) 0.0532 (1.35) SEATING PLANE 0.0098 (0.25) 0.0040 (0.10) 0.0192 (0.49) 0.0138 (0.35) 0.0500 (1.27) BSC 0.0098 (0.25) 0.0075 (0.19) 0.0500 (1.27) 0.0160 (0.41) 8 0 0.0196 (0.50) 0.0099 (0.25) 45 Plastic Mini-DIP Package (N-8) 8 14 5 0.430 (10.92) 0.348 (8.84) 0.280 (7.11) 0.240 (6.10) PIN 1 SEATING PLANE 0.022 (0.558) 0.014 (0.356) 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) MAX 0.130 (3.30) MIN 0.070 (1.77) 0.045 (1.15) 0.100 (2.54) BSC 0.160 (4.06) 0.115 (2.93) 0.325 (8.25) 0.300 (7.62) 0.015 (0.381) 0.008 (0.204) 0.195 (4.95) 0.115 (2.93) |
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Ähnliche Beschreibung - AD22050 |
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