Description
The A1425 AC-coupled Hall-effect sensor IC is a monolithic
integrated circuit that switches in response to changing
differential magnetic fields created by rotating ring magnets
and, when coupled with a magnet, by ferrous targets. The device
is a true zero-crossing detector: the output switches precisely
when the difference in magnetic field strength between the
two Hall elements is zero. A unique dual-comparator scheme
provides for accurate switching at the zero crossing on both the
positive and negative-going regions of the differential signal,
while utilizing hysteresis to prevent false switching. The zero-
crossing nature of this device provides excellent repeatability
and accuracy for crankshaft applications.
Changes in field strength at the device face, which are
induced by a moving target, are sensed by the two integrated
Hall transducers. The transducers generate signals that are
differentially amplified by on-chip electronics. This differential
design provides immunity to radial vibration within the
operating air gap range of the A1425, by rejection of the
common mode signal. Steady-state magnet and system offsets
are eliminated using an on-chip differential band-pass filter.
This filter also provides relative immunity to interference from
electromagnetic sources.
1425-DSa, Rev.4
MCO-0000608
Features and Benefits
▪ Usedinsensingmotionofringmagnetorferroustargets
▪ Integratedfiltercapacitor
▪ Wideoperatingtemperaturerange
▪ Operationwithmagneticinputsignalfrequencyfrom
20 Hz to 20 kHz
▪ ResistanttoEMI
▪ Largeeffectiveairgaps
▪ 4.0to26.5Vsupplyoperatingrange
▪ OutputcompatiblewithbothTTLandCMOSlogic
families
▪ Reversebatteryprotection
▪ Resistanttomechanicalandthermalstress
▪ Accuratetruezero-crossingswitchpoint
High Accuracy Analog Speed Sensor IC with Integrated Filter
Capacitor and Dual Zero-Crossing Output Signal
Continued on the next page…
Package: 4 pin SIP (suffix K)
Functional Block Diagram
A1425
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
February 22, 2019
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
2
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
The device utilizes advanced temperature compensation for the
high-passlter,sensitivity,andSchmitttriggerswitchpoints,
to guarantee optimal operation to low frequencies over a wide
range of air gaps and temperatures.
EachHalleectdigitalintegratedcircuitincludesavoltage
regulator,twoHalleectelements,temperaturecompensating
circuitry,alow-levelamplier,band-passlter,Schmitttrigger,
and an output driver, which requires a pull-up resistor. The on-
board regulator permits operation with supply voltages from 4.0
to26.5V.Theoutputstagecaneasilyswitch20mAoverthefull
frequency response range of the device, and is compatible with
bothTTLandCMOSlogiccircuits.
The device is packaged in a 4-pin plastic SIP. It is lead (Pb) free,
with 100% matte tin plated leadframe.
2 3 41
Terminal List Table
Name Number
VCC 1
VOUT 2
TEST 3
GND 4
Pin-out Diagram
Selection Guide
Part Number Packing
*
Switchpoints
B
RP(MIN)
(G)
B
OP(MAX)
(G)
A1425LK-T
Bulk, 500 pieces/bag
–11 11
*
Contact Allegro for additional packing options.
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
Continuous Output Current I
OUT
25 mA
Continuous Reverse-Output Current I
ROUT
–50 mA
Operating Ambient Temperature T
A
Range L –40 to 150 ºC
Maximum Junction T
J(max)
165 ºC
Storage Temperature T
stg
–65 to 170 ºC
Description (continued)