AD705AQ AD [Analog Devices], AD705AQ Datasheet - Page 8

• Manufacturer Part Number: AD705AQ
• Description: Picoampere Input Current Bipolar Op Amp
• Manufacturer: AD [Analog Devices]

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
0.200 (5.08)
0.125 (3.18)
0.25R
(0.64)
(5.08)
0.200
MAX
0.005 (0.13) MIN
PINS 2 AND 6 OF THE AD705
0.023 (0.58)
0.014 (0.36)
Cerdip (Q) Package
WITHOUT THE NETWORK,
0-15
CAPACITORS C1, C2 AND C3 ARE SOUTHERN ELECTRONICS MPCC,
POLYCARBONATE, 5%, 50 VOLT.
Figure 26. A 1 Hz, 2-Pole Active Filter
ARE TIED TOGETHER.
8
1M
RESISTOR NETWORK
OPTIONAL BALANCE
1
0.405 (10.29) MAX
R1
0.310 (7.87)
0.220 (5.59)
0.32 (8.13)
0.29 (7.37)
(2.54)
0.100
BSC
0.055 (1.4) MAX
0.070 (1.78)
0.030 (0.76)
1M
R2
5
4
0.015 (0.38)
0.008 (0.20)
C2
0.060 (1.52)
0.015 (0.38)
SEATING
PLANE
0.150
(3.81)
MIN
3
2
C1
AD705
2M
R3
–V
+V
4
7
S
S
0.01µF
C3
0.1µF
6
0.1µF
(4.19
0.165
0.125 (3.18)
Dimensions shown in inches and (mm).
Plastic Mini-DIP (N) Package
0.25)
0.01
OUTLINE DIMENSIONS
0.018
PIN 1
(0.46
MIN
0-15
0.003
0.08)
8
1
V
OUT
0.011
0.30 (7.62)
0.39 (9.91)
(0.28
0.100
(2.54)
MAX
TYP
REF
–8–
0.003
0.08)
0.033
(0.84)
Desired Low
Pass Response
Bessel Response
Butterworth Response 1.00
0.1 dB Chebychev
0.2 dB Chebychev
0.5 dB Chebychev
1.0 dB Chebychev
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 F, C2 = 0.037 F.
NOM
4
5
0.035
(0.89
(6.35)
0.25
Table II. Recommended Component Values
for the 1 Hz Low-Pass Filter
0.18
(4.57
Figure 27. V
SEATING
PLANE
0.25)
0.01
–30
–60
–90
(7.87)
90
60
30
0.31
0
–60
0.03
0.76)
–40
BALANCE RESISTOR, R3
WITHOUT OPTIONAL
–20
OS
Pole
Frequency
(Hz)
1.27
0.93
0.90
0.85
0.80
vs. Temperature of 1 Hz Filter
0
(0.203
0.008
TEMPERATURE – C
0.011
(0.269
+20
8-Pin SOIC (R) Package
0.075)
0.004
PIN 1
0.002
+40
WITH OPTIONAL BALANCE
0.03)
Pole Q
0.58
0.707
0.77
0.80
0.86
0.96
+60
RESISTOR, R3
0.0500
8
1
(1.27)
0.193
BSC
(4.90
+80
0.017
(0.42
0.008
0.10)
C1 Value
( F)
0.14
0.23
0.26
0.28
0.32
0.38
0.033
(0.83
+100
5
4
0.07)
0.003
0.154
0.098
(2.49
(3.91
0.43)
0.017
+120
0.236
(6.00
0.23)
0.004
0.10)
0.006
+140
C2 Value
( F)
0.11
0.11
0.11
0.11
0.11
0.10
REV. B
0.012
0.20)