AD628
FILTER CAPACITOR VALUES
KELVIN CONNECTION
Connect a capacitor to Pin 4 (CFILT) to implement a low-pass
filter. The capacitor value is
In certain applications, it may be desirable to connect the
inverting input of an amplifier to a remote reference point.
This eliminates errors resulting in circuit losses in inter-
connecting wiring. The AD628 is particularly suited for this
type of connection. In Figure 35, a 10 kΩ resistor added in the
feedback matches the source impedance of A2. This is
described in more detail in the Gain Adjustment section.
C = 15.9/ft (μF)
where ft is the desired 3 dB filter frequency.
Table 7 shows several frequencies and their closest standard
capacitor values.
Table 7. Capacitor Values for Various Filter Frequencies
Frequency (Hz)
Capacitor Value (μF)
10
1.5
50
0.33
60
0.27
100
400
1 k
5 k
10 k
0.15
0.039
0.015
0.0033
0.0015
+V
S
–IN
100kꢀ
100kꢀ
10kꢀ
10kꢀ
CIRCUIT
LOSS
+IN
A2
–IN
OUT
G = +0.1
A1
–IN
+IN
10kꢀ
R
G
LOAD
+IN
10kꢀ
AD628
V
REF
C
FILT
–V
S
V
/2
S
Figure 35. Kelvin Connection
Rev. G | Page 19 of 20
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