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AD22050RZ-REEL7 View Datasheet(PDF) - Analog Devices

Part Name
Description
View to exact match
AD22050RZ-REEL7
ADI
Analog Devices ADI
AD22050RZ-REEL7 Datasheet PDF : 8 Pages
1 2 3 4 5 6 7 8
ANALOG
OUTPUT
+IN OFS +VS OUT
VDM
AD22050
–IN GND A1 A2
CORNER
FREQUENCY
= 2C
1
؋
100k
THAT IS, 1.59Hz-F
(C IS IN FARADS)
VCM
C
ANALOG
COMMON
Figure 6. Connections for Single-Pole, Low-Pass Filter
If the gain is raised using a resistor, as shown in Figure 5, the
corner frequency is lowered by the same factor as the gain is
raised. Thus, using a resistor of 200 k(for which the gain
would be doubled) the corner frequency is now 0.796 Hz-µF,
(0.039 µF for a 20 Hz corner).
ANALOG
OUTPUT
+IN OFS +VS OUT
VDM
AD22050
C
–IN GND A1 A2
255k
CORNER
FREQUENCY = 1Hz-F
VCM
C
ANALOG
COMMON
Figure 7. Connections for Conveniently Scaled, Two-Pole,
Low-Pass Filter
A two-pole filter (with a roll-off of 40 dB/decade) can be imple-
mented using the connections shown in Figure 7. This is a
Sallen & Key form based on a ×2 amplifier. It is useful to remem-
ber that a two-pole filter with a corner frequency f2 and a
one-pole filter with a corner at f1 have the same attenuation at
the frequency (f22/f1). The attenuation at that frequency is
40 Log(f2/f1). This is illustrated in Figure 8. Using the standard
resistor value shown, and equal capacitors (in Figure 7), the
corner frequency is conveniently scaled at 1 Hz-µF (0.05 µF for
a 20 Hz corner). A maximally flat response occurs when the
resistor is lowered to 196 kand the scaling is then 1.145 Hz-
µF. The output offset is raised by about 4 mV (equivalent to
200 µV at the input pins).
FREQUENCY
ATTENUATION
–40dB/DECADE
–20dB/DECADE
40LOG (f2/f1)
A 1-POLE FILTER, CORNER f1,
AND A 2-POLE FILTER, CORNER f2,
HAVE THE SAME ATTENUATION,
–40LOG (f2/f1), AT FREQUENCY f22/f1
f1
f2
(f22/f1)
Figure 8. Comparative Responses of One- and Two-Pole
Low-Pass Filters
AD22050
A three-pole filter (with roll-off 60 dB/decade) can be formed by
adding a passive RC network at the output forming a real pole.
A three-pole filter with a corner frequency f3 has the same
attenuation a one-pole filter of corner f1 has at a frequency
f33/f1, where the attenuation is 30 Log (f3/f1) (see the graph in
Figure 9). Using equal capacitor values, and a resistor of
160 k, the corner-frequency calibration remains 1 Hz-µF.
FREQUENCY
ATTENUATION
–20dB/DECADE
–60dB/DECADE
30LOG (f3/f1)
A 1-POLE FILTER, CORNER f1,
AND A 3-POLE FILTER, CORNER f3,
HAVE THE SAME ATTENUATION,
–30LOG (f3/f1), AT FREQUENCY (f33/f1)
f1
f3
(f33/f1)
Figure 9. Comparative Responses of One- and Three-Pole
Low-Pass Filters
CURRENT SENSOR INTERFACE
A typical automotive application making use of the large
common-mode range is shown in Figure 10.
+VS (BATTERY)
SOLENOID
LOAD
FLYBACK
DIODE
100m
+IN OFS +VS OUT
AD22050
–IN GND A1 A2
CMOS DRIVER
CHASSIS
C
POWER
DARLINGTON
+5V
ANALOG OUTPUT
4V PER AMP
191k
20k
؎5% SENSOR
CALIBRATION
CORNER FREQUENCY
= 0.796Hz-F
(0.22F FOR f = 3.6Hz)
ANALOG COMMON
Figure 10. Current Sensor Interface. Gain Is ×40, Single-
Pole Low-Pass Filtering
The current in a load, here shown as a solenoid, is controlled by
a power transistor that is either cut off or saturated by a pulse at
its base; the duty-cycle of the pulse determines the average
current. This current is sensed in a small resistor. The aver-
age differential voltage across this resistor is typically 100 mV,
although its peak value will be higher by an amount that
depends on the inductance of the load and the control fre-
quency. The common-mode voltage, on the other hand, extends
from roughly 1 V above ground, when the transistor is satu-
rated, to about 1.5 V above the battery voltage, when the tran-
sistor is cut off and the diode conducts.
If the maximum battery voltage spikes up to +20 V, the common-
mode voltage at the input can be as high as 21.5 V. This can be
measured using even a +5 V supply for the AD22050.
REV. C
–5–
 

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