A1425_05 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 with Integrated Filter Capacitor
and Dual Zero-Crossing Output Signal
Package K, 4-pin SIP
1234
1. VCC
2. VOUT
3. TEST
4. GND
The A1425 ac-coupled Hall-effect sensor 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-com-
parator scheme provides for accurate switching at the zero crossing on both the
positive and negative-going regions of the differential signal, while utilizing hys-
teresis 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
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 filter.
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 Hall effect digital integrated circuit includes a voltage regulator, two Hall
effect sensing elements, temperature compensating circuitry, a low-level amplifier,
band-pass filter, 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 sensor, and is compatible with both TTL and CMOS logic
circuits.
The device is packaged in a 4-pin plastic SIP. The lead (Pb) free version (suffix
–T) has a 100% matte tin plated leadframe.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage*, V_CC ........................................ 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 Temperature
Ambient, T_A................................ –40ºC to 150ºC
Maximum Junction, T_J(max)........................165ºC
Storage Temperature, T_S .................. –65ºC to 170ºC
*Refer to Power Derating section.
Features and Benefits
• Senses 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
A1425a-DS
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com