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A1422 Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer A1422
Beschreibung High Precision Hall Effect AC-Coupled Differential Sensor IC
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 15 Seiten
A1422 Datasheet, Funktion
A1421, A1422, and A1423
High Precision Hall Effect AC-Coupled Differential Sensor IC
with Integrated Filter Capacitor
Features and Benefits
Integrated tracking capacitor
Used for sensing motion of ring magnet or ferrous targets
• Wide operating temperature range
• Operation with magnetic input signal frequency from
20 Hz to 30 kHz
• EMI/ESD-resistant
• Large effective air gaps
• 4.0 to 26.5 V supply operating range
• Output compatible with CMOS logic families
• Reverse battery protection
• Resistant to mechanical and thermal stress
• Accurate true zero crossing switchpoint (A1421 only)
• High vibration immunity, in running mode (A1423 only)
Package: 4 pin SIP (suffix K)
Description
The A1421, A1422, and A1423 are AC-coupled Hall-effect
sensor ICs which include monolithic integrated circuits that
switch in response to changing differential magnetic fields
created by rotating ring magnets or, when coupled with a
magnet, by ferrous targets. This family of devices also includes
an integrated capacitor that provides the high accuracy of analog
sensing without an external filter capacitor. This reduces cost
and components, while improving the reliability of the final
sensor solution.
Magnetic field changes affect the two integrated Hall
transducers and then are differentially amplified on the chip.
Differential design provides immunity to radial vibration,
within the device operating air gap range, by rejection of this
common-mode signal change. Steady-state system offsets
are eliminated using an on-chip differential bandpass filter
with integrated capacitor. This filter also provides relative
immunity to interference from electromagnetic sources. The
device utilizes advanced temperature compensation for the
high-pass filter, sensitivity, and Schmitt trigger switchpoints
to guarantee optimal operation to low frequencies over a wide
range of air gaps and temperatures.
Not to scale
Continued on the next page…
VS+
VCC
(Pin 1)
Functional Block Diagram
Dual Hall
Transducers
Regulator
0.1 uF
Hall
Amp
Gain
Stage
Bandpass Filter Integrated
Tracking Capacitor
VREF
Diagnostic
Circuitry
Comparator
TEST
(Pin 3)
VOUT
(Pin 2)
A1421a-DS, Rev. 4
GND
(Pin 4)
(Required)






A1422 Datasheet, Funktion
A1421, A1422,
and A1423
High Precision Hall Effect AC-Coupled Differential
Sensor IC with Integrated Filter Capacitor
Empirical Results
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
–50
ICC(OFF) by TA
Over VCC Range
VCC (V)
4.5
12.0
20.0
0 50 100 150
Ambient Temperature, TA (ºC)
200
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
–50
ICC(ON) by TA
Over VCC Range
VCC (V)
4.5
12.0
20.0
0 50 100 150
Ambient Temperature, TA (ºC)
200
500
450
400
350
300
250
200
150
100
50
0
–50
VOUT(SAT) by TA
Over VCC Range; ISINK = 20 mA
VCC (V)
4.5
12.0
20.0
0 50 100 150
Ambient Temperature, TA (ºC)
200
Continued on next page.
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
ICC(OFF) by VCC
Over TA Range
TA (ºC)
150
25
–40
5 10 15 20
Supply Voltage, VCC (V)
25
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
ICC(ON) by VCC
Over TA Range
TA (ºC)
150
25
–40
5 10 15 20
Supply Voltage, VCC (V)
25
500
450
400
350
300
250
200
150
100
50
0
0
VOUT(SAT) by VCC
Over TA Range; ISINK = 20 mA
TA (ºC)
150
25
–40
5 10 15 20
Supply Voltage, VCC (V)
25
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6

6 Page









A1422 pdf, datenblatt
A1421, A1422,
and A1423
High Precision Hall Effect AC-Coupled Differential
Sensor IC with Integrated Filter Capacitor
Applications Information
The A1421, A1422, and A1423 are versatile high-precision dif-
ferential sensor ICs that can be used in a wide range of applica-
tions. Proper choice of the target material and shape, magnet
material and shape, and assembly techniques enables large
working air gaps and high switchpoint accuracy over the device
operating temperature range.
Device Operation
The device IC contains two integrated Hall transducers that are
used to differentially respond to a magnetic field across the sur-
face of the IC. Referring to figure 1, which shows curves for the
A1421 as an example, the trigger switches the output when the
differential magnetic field crosses the BOP level while increasing
in strength (referred to as the positive direction). In the example,
the A1421 output voltage switches high (off), and switches the
output low (on) when the differential magnetic field crosses BRP
while decreasing (the negative direction).
The operation is achieved through the use of two separate com-
parators. One comparator has a positive hysteresis, BHYS1, and
the other a negative hysteresis, BHYS2. Therefore, one comparator
switches at the BOP crossing on an increasing differential signal
and the other switches at the BRP crossing on a decreasing differ-
ential signal. The hysteresis on each comparator precludes false
switching on noise or target jitter.
The behavior is similar for the A1422 and the A1423. The
switchpoints are as shown in the magnetic charactersitics table,
and the output polarity is inverted. This is illustrated in figure 2,
on the next page.
Start-up
During power-on time, tPO, the output signal, VOUT, is high.
Beyond this time, if the applied magnetic field, Bdiff, is smaller
than BHYS, the switching state and VOUT polarity are indeter-
minate. VOUT will be valid for Bdiff > BHYS, after the additional
settling time, tSettling, has also elapsed.
Delay
The bandpass filter induces delay in the output signal, VOUT, rel-
ative to the applied magnetic field, Bdiff. Simulation data shown
Applied Magnetic 15.0
Field, Bdiff 0.0
BRP(typ)1421
BHYS1
B OP(typ)1421
BHYS2
Comparator 1, A1421
Comparator 2, A1421
1421 Switching State
1421 Output Signal, VOUT
Off
Off
On
Figure 1. Typical output characteristics with dual comparator operation. The example shown is for the A1421. Characteristics
shown without delay, see characteristic data charts for delay and phase shift contributions.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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