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. A1421a-DS, Rev. 4 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 VS+ Diagnostic Circuitry Gain Stage Dual Hall Transducers Comparator TEST (Pin 3) (Required) VREF

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 2 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 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 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...

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 3 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com further from the zero-crossing. The output polarities are shown in the Product Selection Guide table. This variety of options provides flexibility for achieving solutions 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...

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 4 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com OPERATING CHARACTERISTICS, continued Valid at TA = – 40ºC to 150ºC, TJ 165°C; over operational air gap range and VCC within operating range, unless otherwise noted. Typical operating parameters: VCC = 12 V and TA = 25°C. Characteristic Symbol Test Conditions Min. Typ. Max. Units MAGNETIC CHARACTERISTICS5,6 Operate Point BOP 1421, Bdiff increasing, fBdiff...

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 5 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information Characteristic Symbol Test Conditions* Value Units Package Thermal Resistance RèJA Minimum-K PCB (single-sided with copper limited to solder pads) 177 ºC/W *In still air. Additional thermal information available on Allegro Web site. 20 40 60 80 100 120 140...

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 7 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Simulation Results Continued on next page.

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 8 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Simulation Results, continued Continued on next page.

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 9 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Simulation Results, continued Continued on next page.

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 10 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Simulation Results, continued

High Precision Hall Effect AC-Coupled Differential Sensor IC with Integrated Filter Capacitor A1421, A1422, and A1423 Allegro MicroSystems, Inc. 11 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com Device Evaluation: EMC Characterization Test Name Reference Specifi cation ESD – Human Body Model* AEC-Q100-002 ESD – Machine Model AEC-Q100-003 Conducted Transients ISO 7637-1 Direct RF Injection ISO 11452-7 Bulk Current Injection ISO 11452-4 TEM Cell ISO 11452-3 *ESD test is done with no external components. Please contact Allegro MicroSystems for...