AD705 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD705 Datasheet PDF : 8 Pages
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AD705
A 1 Hz, 2-Pole, Active Filter
Table II gives recommended component values for the 1 Hz fil-
ter of Figure 26. An unusual characteristic of the AD705 is that
both the input bias current and the input offset current and their
drift remain low over most of the op amps rated temperature
range. Therefore, for most applications, there is no need to use
the normal balancing resistor tied between the noninverting ter-
minal of the op amp and ground. Eliminating the standard bal-
ancing resistor reduces board space and lowers circuit noise.
However, this resistor is needed at temperatures above 110°C,
because input bias current starts to change rapidly, as shown by
Figure 27.
INPUT
R1
1MΩ
R2
1MΩ
C2
OPTIONAL BALANCE
RESISTOR NETWORK
WITHOUT THE NETWORK,
PINS 2 AND 6 OF THE AD705
ARE TIED TOGETHER.
C1
+VS
3
7
AD705
2
4
0.1µF
6
0.1µF
–VS
R3
2MΩ
C3
0.01µF
VOUT
Table II. Recommended Component Values
for the 1 Hz Low-Pass Filter
Desired Low
Pass Response
Pole
Pole Q C1 Value C2 Value
Frequency
(Hz)
(F)
(F)
Bessel Response
1.27
Butterworth Response 1.00
0.1 dB Chebychev 0.93
0.2 dB Chebychev 0.90
0.5 dB Chebychev 0.85
1.0 dB Chebychev 0.80
0.58 0.14
0.11
0.707 0.23
0.11
0.77 0.26
0.11
0.80 0.28
0.11
0.86 0.32
0.11
0.96 0.38
0.10
Specified values are for a –3 dB point of 1.0 Hz. For other frequencies,
simply scale capacitors C1 and C2 directly; i.e., for 3 Hz Bessel response,
C1 = 0.046 µF, C2 = 0.037 µF.
90
WITHOUT OPTIONAL
60
BALANCE RESISTOR, R3
30
0
WITH OPTIONAL BALANCE
–30
RESISTOR, R3
–60
CAPACITORS C1, C2 AND C3 ARE SOUTHERN ELECTRONICS MPCC,
POLYCARBONATE, ±5%, 50 VOLT.
–90
–60 –40 –20
0 +20 +40 +60 +80 +100 +120 +140
TEMPERATURE – °C
Figure 26. A 1 Hz, 2-Pole Active Filter
Figure 27. VOS vs. Temperature of 1 Hz Filter
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
Cerdip (Q) Package
0.005 (0.13) MIN
0.055 (1.4) MAX
8
5
0.25R
(0.64)
1
4
0.200
(5.08)
MAX
0.200 (5.08)
0.125 (3.18)
0.405 (10.29) MAX
0.060 (1.52)
0.015 (0.38)
0.150
(3.81)
MIN
0.023 (0.58) 0.100 0.070 (1.78)
0.014 (0.36) (2.54) 0.030 (0.76)
BSC
SEATING
PLANE
0.310 (7.87)
0.220 (5.59)
Plastic Mini-DIP (N) Package
8
PIN 1
1
5
0.25 0.31
(6.35) (7.87)
4
0.165 ± 0.01
(4.19 ± 0.25)
0.39 (9.91)
MAX
0.035 ± 0.01
(0.89 ± 0.25)
0.125 (3.18)
MIN
0.018 ± 0.003
(0.46 ± 0.08)
0.100
(2.54)
TYP
0.033
(0.84)
NOM
0.30 (7.62)
REF
0.18 ± 0.03
(4.57 ± 0.76)
SEATING
PLANE
8-Pin SOIC (R) Package
8
PIN 1
1
5
0.154 ± 0.004
(3.91 ± 0.10)
4
0.236 ± 0.012
(6.00 ± 0.20)
0.008 ± 0.004
(0.203 ± 0.075)
0.193 ± 0.008
(4.90 ± 0.10)
0.098 ± 0.006
(2.49 ± 0.23)
0.0500 0.017 ± 0.003
(1.27) (0.42 ± 0.07)
BSC
0.011 ± 0.002
(0.269 ± 0.03)
0.033 ± 0.017
(0.83 ± 0.43)
0.32 (8.13)
0.29 (7.37)
0-15 °
0.015 (0.38)
0.008 (0.20)
0.011 ± 0.003
(0.28 ± 0.08)
0-15 °
–8–
REV. B
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