A1425 Datasheet, PDF (1/13 Pages) Allegro MicroSystems – High Accuracy Analog Speed Sensor with Integrated Filter Capacitor and Dual Zero-Crossing Output Signal

A1425
High Accuracy Analog Speed Sensor IC with Integrated Filter
Capacitor and Dual Zero-Crossing Output Signal
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
Package: 4 pin SIP (suffix K)
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.
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V_S+
VCC
(Pin 1)
Functional Block Diagram
Dual Hall
Transducers
Regulator
0.1 uF
Hall
Amp
Gain
Stage
Bandpass Filter Integrated
Tracking Capacitor
V_REF
Diagnostic
Circuitry
Comparator
TEST
(Pin 3)
VOUT
(Pin 2)
1425-DSa, Rev.3
GND
(Pin 4)
(Required)