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AD22050R-REEL7 View Datasheet(PDF) - Analog Devices

Part Name
Description
View to exact match
AD22050R-REEL7
ADI
Analog Devices ADI
AD22050R-REEL7 Datasheet PDF : 8 Pages
1 2 3 4 5 6 7 8
AD22050
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 Mif 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 kresistor 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 R13ʈR14. 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, 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 R13ʈR14, 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 kload 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.
+VS A1
A2
AD22050
R1
R18
C1
R12
200k
1k
5pF
100k
IN+
R19 1k
A1
A2
IN–
R2
200k
R8
9k
R3
41k
R5
2.6k
R4
41k
C2
5pF R9
10k
R17
95k
R15
10k
R11
2k
R6
250k
R7
250
R16
10k
R14
20k
R10
2k
R13
20k
OUT
GND
OFS
Figure 16. Simplified Schematic of AD22050, Including Component Values
Plastic Mini-DIP Package
(N-8)
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
Plastic SOIC Package
(SO-8)
0.430 (10.92)
0.348 (8.84)
8
5
0.280 (7.11)
0.240 (6.10)
1
4
0.325 (8.25)
PIN 1
0.060 (1.52)
0.300 (7.62)
0.210 (5.33)
0.015 (0.38)
MAX
0.130
0.160 (4.06)
(3.30)
0.115 (2.93)
MIN
0.022 (0.558) 0.100 0.070 (1.77)
0.014 (0.356) (2.54) 0.045 (1.15)
SEATING
PLANE
BSC
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
0.1968 (5.00)
0.1890 (4.80)
8
0.1574 (4.00)
0.1497 (3.80) 1
5
0.2440 (6.20)
4 0.2284 (5.80)
PIN 1
0.0098 (0.25)
0.0040 (0.10)
0.0688 (1.75)
0.0532 (1.35)
0.0196 (0.50)
0.0099 (0.25)؋ 45؇
SEATING
PLANE
0.0500 0.0192 (0.49)
(1.27) 0.0138 (0.35)
BSC
0.0098 (0.25)
0.0075 (0.19)
8؇
0؇ 0.0500 (1.27)
0.0160 (0.41)
–8–
REV. C
 

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