A1421

• Integrated tracking capacitor
• Senses 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 both TTL and 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)

The A1421, A1422 and A1423 are ac-coupled Hall-effect sensors 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. A1421, A1422 and A1423 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 of A1421, A1422 and A1423 are sensed by two integrated Hall transducers and then are differentially amplified on the chip. Differential sensing 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. A1421, A1422 and A1423 utilize 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.

A1421, A1422 and A1423 include: 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 of A1421, A1422 and A1423 can switch 20 mA over the full frequency response range of the sensor, and is compatible with TTL and CMOS logic circuits.

A1421, A1422 and A1423 in this family differ from each other in their switchpoint specifications and their switching polarity. The A1421 has a small hysteresis and asymmetrical switchpoints, with one switchpoint at the zero-crossing. The A1422 has a small hysteresis and symmetrical switchpoints, both near the zero-crossing. The A1423 offers high vibration immunity, by means of its larger hysteresis that establishes symmetrical switchpoints 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.

A1421, A1422 and A1423 package has an operating ambient temperature range 40 °C to 150°C , and is provided in a 4-pin plastic SIP. Each package is available in a lead (Pb) free version (suffix, T), with a 100% matte tin plated leadframe.