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 Hall-effect gear-tooth sensors with integrated filter capacitors
Allegro MicroSystems Europe has introduced a new family of AC-coupled Hall-effect gear-tooth sensors, the A142x Series, which combine a compact package size with integrated filter capacitors to provide additional reliability.
The A1421LK, A1422LK, and A1423LK are AC-coupled Hall-effect gear-tooth sensors with monolithic integrated circuits that switch in response to changing differential magnetic fields created by a moving ring magnet or by a ferrous target when back-biased with a magnet. These devices are ideal for use in speed, position and timing applications such as automotive transmission and engine management or industrial speed measurement.
The addition of an integrated filter capacitor allows high-accuracy analogue sensing to be achieved without the need for additional external components, thus improving overall system reliability.
Each device incorporates two integrated Hall transducers, which sense changes in magnetic fields and generate signals which are differentially amplified by on-chip electronics. Differential sensing provides immunity to radial vibration within the device’s operating air-gap range by rejection of the common-mode signal change. Steady-state system offsets are eliminated using an on-chip differential band-pass filter, which also provides relative immunity to interference from electromagnetic sources.
Also included are a voltage regulator, temperature-compensating circuitry, a low-level amplifier, Schmitt trigger, and an output driver that requires a pull-up resistor. The on-board regulator permits operation with supply voltages of 4.0-26.5 V. The output stage can easily switch 20 mA over the full frequency response range of the sensor, and is compatible with bipolar and MOS logic circuits.
The A142x family features advanced temperature compensation for the high-pass filter, sensitivity, and Schmitt trigger switchpoints to guarantee optimal operation down to low frequencies over a wide range of air gaps and temperatures.
The devices differ in their switchpoints: the A1421 provides one zero crossing; the A1422 includes narrow-set and symmetric switch points; and the A1423 offers high vibration immunity with its wide-set switchpoints. This variety of options gives the flexibility to suit a wide variety of applications, including transmission and crankshaft speed sensing.
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