A1425
A1425-DS Rev. 0b
Worcester, Massachusetts 01615-0036 (508) 853-5000
115 Northeast Cutoff, Box 15036
www.allegromicro.com
Allegro MicroSystems, Inc.
AB SO LUTE MAX I MUM RAT INGS
Supply Voltage, V
CC
..........................................28 V
Reverse-Supply Voltage, V
RCC
........................–18 V
Output Current, I
OUT
.......................................25 mA
Reverse-Output Current, I
ROUT
.....................–50 mA
Reverse-Output Voltage, V
ROUT
...................–50 mA
Operating Temperature
Ambient, T
A
................................–40ºC to 150ºC
Maximum Junction, T
J(max)
........................165ºC
Storage Temperature, T
S
..................–65ºC to 170ºC
Use the following complete part number when ordering:
Package K, 4-pin SIP
Features and Benefi ts
The A1425 ac-coupled Hall-effect sensor is a monolithic integrated circuit that
switches in response to changing differential magnetic fi elds created by rotating
ring magnets or, 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 fi eld strength between the two Hall elements is zero. A unique dual-
comparator scheme provides for accurate switching during zero-crossing, both
when the sensed fi eld is increasing in strength and when it is decreasing, while
utilizing hysteresis to prevent false switching. The zero-crossing nature of this
device provides excellent repeatability for crankshaft applications.
Changes in fi eld strength at the device face caused by a moving target are sensed
by the two integrated Hall transducers, generating signals that are differen-
tially amplifi ed by on-chip electronics. This differential sensing 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 fi lter. This fi lter also provides
relative immunity to interference from electromagnetic sources.
The device utilizes advanced temperature compensation for the high-pass fi lter,
sensitivity, and the Schmitt trigger switchpoints, guaranteeing optimal operation to
low frequencies over a wide range of air gaps and temperatures.
Each Hall effect digital integrated circuit includes a voltage regulator, two Hall
effect sensing elements, temperature compensating circuitry, a low-level ampli-
fi er, band-pass fi lter, Schmitt trigger, and an output driver. 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 sensor, and is
compatible with both TTL and CMOS logic circuits.
The device is packaged in a 4-pin plastic SIP (part number suffi x -K).
• Senses motion of ring magnet targets
• Integrated fi lter capacitor
• Wide operating temperature range
• Operation with frequency of sensed transitions from 20 Hz to 30 kHz
• EMI-resistant
• Large working air gaps
• 4.0 to 26.5 V operating range
• Output compatible with both TTL and CMOS logic families
• Reverse battery protection
Part Number Package Ambient (ºC)
A1425LK 4-pin plastic SIP –40 to 150
1. VCC
2. VOUT
3. Test pin, tie to GND
4. GND
1234
High Accuracy Analog Speed Sensor with Integrated Filter Capacitor
and Dual Zero-Crossing Output Signal
Preliminary Data Sheet
Subject to Change Without Notice
November 10, 2004
Engineering samples available on a limited basis. Contact your local
sales or applications support offi ce for additional information.