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.
Each device includes: a voltage regulator, two Hall
transducers, temperature compensating circuitry, a low-level
amplifier, bandpass filter, Schmitt trigger, and an output
driver. The on-board regulator permits operation with supply
A1421a-DS, Rev. 7
MCO-0000189
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)
High Precision Hall Effect AC-Coupled Differential Sensor IC
with Integrated Filter Capacitor
Continued on the next page…
PACKAGE: 4 pin SIP (suffix K)
Functional Block Diagram
Not to scale
A1421, A1422, and A1423
Hall
Amp
Regulator
Bandpass Filter Integrated
Tracking Capacitor
VOUT
(Pin 2
)
VCC
(Pin 1)
GND
(Pin 4)
0.1 uF
V
S
+
Diagnostic
Circuitry
Gain
Stage
Dual Hall
Transducers
Comparator
TEST
(Pin 3)
(Required)
V
REF
July 2, 2018
High Precision Hall Effect AC-Coupled Differential
Sensor IC with Integrated Filter Capacitor
A1421, A1422,
and A1423
2
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
voltages from 4.0 to 26.5 V. The output stage can switch 20 mA
over the full frequency response range of the device, and is
compatible with CMOS logic circuits.
The devices in this family differ from each other in their
switchpoint specifications and their switching polarity. The
A1421 has a small hysteresis and asymmetrical switchpoints,
with one switchpoint at the zero-crossing. The A1422 has a small
hysteresis and symmetrical switchpoints, both near the zero-
crossing. The A1423 offers high vibration immunity, by means
of its larger hysteresis that establishes symmetrical switchpoints
further from the zero-crossing. The output polarities are shown in
the Selection Guide table.
This variety of options provides flexibility for achieving solu-
tions for a wide range of applications, including automotive
transmission and crankshaft speed sensing.
The device package has an operating ambient temperature range
–40°C to 150°C , and is provided in a 4-pin plastic SIP. Each
package is available in a lead (Pb) free version (suffix, –T) , with
a 100% matte tin plated leadframe.
ABSOLUTE MAXIMUM RATINGS
Characteristic Symbol Notes Rating Units
Supply Voltage V
CC
Refer to Power Derating section 28 V
Reverse Supply Voltage V
RCC
–18 V
Output Current I
OUT
25 mA
Reverse-Output Current I
ROUT
–50 mA
Operating Ambient Temperature T
A
Range L –40 to 150 °C
Maximum Junction Temperature T
J(max)
165 °C
Storage Temperature T
stg
–65 to 170 °C
DESCRIPTION (continued)
SELECTION GUIDE
Part Number
Output Switching
at B
DIFF
= 0
Switchpoints Symmetry
Packing
[1]
B
Di
Increasing
B
Di
Decreasing
B
OP(typ)
(G)
B
RP(typ)
(G)
B
OP(max)
+
B
RP(min)
(G)
B
OP(typ)
+
B
RP(typ)
(G)
B
OP(min)
+
B
RP(max)
(G)
A1421LK-T
[2]
Low (On) to
High (O)
High (O) to
Low (On)
15 0 15 15 7.5
Bulk, 500
pieces/bag
A1422LK-T
High (O) to
Low (On)
Low (On) to
High (O)
15 –15 0 0 0
A1423LK-T
High (O) to
Low (On)
Low (On) to
High (O)
65 –65 0 0 0
[1]
Contact Allegro for additional packing options.
[2]
A1421LK-T is DISCONTINUED. This classification indicates that the product is obsolete and is no longer in production. Samples are no longer available.
Date of status change: July 2, 2018. For existing customer transition, and for new customers or new applications, contact Allegro Sales.
Pinout Diagram
2 3 41
Terminal List Table
Number Name
1 VCC
2 VOUT
3 TEST
4 GND