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A1102LLHLT

A1102LLHLT - Unipolar Hall Effect Switch, 180G Trip, SOT-23W

The Allegro MicroSystems A1102LLHLT is a continuous-time unipolar Hall-effect digital switch with open-drain output, delivered in a 3-pin SOT-23W surface-mount package. It operates across a 3.8 V to 24 V supply range, switches at a 180 Gauss (typ.) magnetic trip point with a 125 Gauss release point, and is qualified to the extended -40 °C to +150 °C automotive temperature range. A Hall-effect switch is a magnetic sensor whose output changes state when the applied magnetic flux density crosses a programmed threshold. Compared with reed switches, Hall ICs offer solid-state reliability, sub-microsecond response, and integration of the sensing element, signal conditioning, and output driver in a single silicon die. The A1102 belongs to Allegro's continuous-time family: the on-chip oscillator drives a dynamic-cancellation chopper-stabilized Hall plate, eliminating the residual offset of DC-biased Hall elements and yielding a stable switch point over temperature and supply. Key features include a south-pole-only unipolar transfer function (output turns on when |B| exceeds Bop and off when |B| falls below Brp), 20 kHz typical chopping frequency for clean output, low quiescent current, 30 V absolute-maximum supply tolerance, and reverse-battery protection on the supply pin. The open-drain output requires an external pull-up resistor, simplifying interface to 3.3 V, 5 V, or 12 V logic rails without level shifting. Architecturally, the device combines a BiCMOS Hall sensing front-end, a precision comparator with trimmed thresholds, an open-drain DMOS output stage, and on-chip protection (reverse-supply, over-voltage, and output ESD). The BiCMOS process enables fast power-on (<10 µs) and low-noise operation without the offset drift seen in older bipolar Hall ICs, while the chopper-stabilized front end virtually eliminates the residual offset that would otherwise shift the switch point with mechanical stress. Typical applications include automotive seat-belt buckle detection, gear-shift and transmission position sensing, BLDC motor commutation triggers, valve and solenoid position feedback, consumer appliance lid/door interlocks, and contactless limit switches. The wide 3.8 V-24 V supply range allows direct connection to 12 V automotive rails without an upstream regulator. Designers should provide a bypass capacitor of at least 0.1 µF close to the supply pin and a pull-up resistor (typically 10 kΩ) on the output. Place the device so the brand-side marking aligns with the target magnet's pole direction; the sensitive axis is perpendicular to the package top. This page synthesizes distributor pricing, drop-in SOT-23W alternatives, and practical design notes that the manufacturer datasheet alone does not aggregate.