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PDF AD22057 Data sheet ( Hoja de datos )
| Número de pieza | AD22057 | |
| Descripción | Single-Supply Sensor Interface Amplifier | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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FEATURES
Gain of ؋20. Alterable from ؋1 to ؋160
Input CMR from Below Ground to 6؋ (VS – 1 V)
Output Span 20 mV to (VS – 0.2) V
1-, 2-, 3-Pole Low-Pass Filtering Available
Accurate Midscale Offset Capability
Differential Input Resistance 400 k⍀
Drives 1 k⍀ Load to +4 V Using VS = +5 V
Supply Voltage: +3.0 V to +36 V
Transient Spike Protection and RFI Filters Included
Peak Input Voltage (40 ms): 60 V
Reversed Supply Protection: –34 V
Operating Temperature Range: –40؇C to +125؇C
APPLICATIONS
Current Sensing
Motor Control
Interface for Pressure Transducers, Position Indicators,
Strain Gages, and Other Low Level Signal Sources
Accelerometers
Single-Supply Sensor
Interface Amplifier
AD22057
FUNCTIONAL BLOCK DIAGRAM
+VS OFS A1 A2
AD22057
IN+
A1
IN–
A2 OUT
GND
GENERAL DESCRIPTION
The AD22057 is a single-supply difference amplifier for ampli-
fying and low-pass filtering small differential voltages (typically
100 mV FS at a gain of 40) from sources having a large common-
mode voltage.
Supply voltages from +3.0 V to +36 V can be used. The input
common-mode range extends from below ground to +24 V using
a +5 V supply with excellent rejection of this common-mode
voltage. This is achieved by the use of a special resistive attenua-
tor at the input, laser trimmed to a very high differential balance.
Provisions are included for optional low-pass filtering and gain
adjustment. An accurate midscale offset feature allows bipolar
signals to be amplified.
+VS (CAR BATTERY)
SOLENOID
LOAD
+5V
ANALOG OUTPUT
4V PER AMP
100m⍀
AD22057
200k⍀
CMOS DRIVER
CORNER FREQUENCY
= 0.796Hz-F
C
CHASSIS
POWER
DARLINGTON
SINGLE-POLE LOW-PASS FILTERING, GAIN: 40
ANALOG GROUND
Figure 1. Typical Application Circuit for a Current Sensor Interface
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1999
1 page  
AD22057
frequency will increase; it should be calculated using the parallel
sum of the resistor and 100 kΩ.
ANALOG
OUTPUT
+IN OFS +VS OUT
VDM AD22057
–IN GND A1 A2
CORNER
FREQUENCY
=
2C
1
؋ 100k⍀
THAT IS, 1.59Hz-F
VCM
C
(C IS IN FARADS)
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 kΩ (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
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 kΩ, 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)
+IN OFS +VS OUT
VDM AD22057
C
–IN GND A1 A2
255k⍀
CORNER
FREQUENCY = 1Hz-F
f1 f3 (f33/f1)
Figure 9. Comparative Responses of One- and Three-Pole
Low-Pass Filters
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 kΩ and 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
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
AD22057
–IN GND A1 A2
CMOS DRIVER
CHASSIS
POWER
DARLINGTON
C
+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 AD22057.
REV. A
–5–
5 Page | ||
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| PDF Descargar | [ Datasheet AD22057.PDF ] | |
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