Dual-channel switch interface IC for Hall-effect sensor systems

20th June 2007

ES Admin

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The new A6850 from Allegro MicroSystems Europe is a dual-channel switch interface IC designed to simplify the implementation of two-wire Hall-effect sensor systems in automotive applications. The new device eliminates the need for an external sense resistor and comparator, thereby reducing system costs. The elimination of the sense resistor also results in a subsequent elimination of the voltage drop across the resistor, which can enable sensing systems to operate down to lower battery voltages.

The A6850 offers two channels integrated on a single IC as well as benefits such as current clamping, thermal protection, and a low operating current 'sleep' mode. It is rated over a wide operating voltage and temperature range, making it an excellent fit for various automotive sensing systems. It
can also be used to interface with mechanical switches.

Protected high-side low-resistance DMOS MOSFETs are used to switch the supply voltage to the two Hall-effect devices. Each switch can be controlled independently via individual 'enable' pins, and both switches are protected with current-limiting circuitry. The output switches are rated to operate at
up to 26.5 V and will source at least 25 mA per channel before current limiting.

The A6850 acts as a logic-enabled high-side switch to the sensor. This high-side switching is the preferred method in automotive systems owing to the better protection it affords if there are short-to-ground conditions on the sensor.

Typical two-wire Hall sensor applications require the user to measure the supply current to determine whether the Hall sensor is switched on (magnetic field present) or switched off (no magnetic field present). This is usually accomplished by using an external series shunt resistor. The A6850 eliminates the need for the external series shunt resistor by incorporating an integrated current mirror which reports the Hall sensor supply current as a one-tenth value on the 'sense' output pins.

A key benefit of this implementation is that the input supply voltage on the sensor can be run down to as little as 4.2 V. In addition, the ground side of the Hall sensor can be tied directly to the chassis ground, allowing a single-wire solution from the control board to the sensor.

The low current (less than 15 µA) 'sleep' mode is activated by driving both 'enable' pins low.

The primary application for the new device will be in automotive occupancy detection systems, which sense seatbelt buckle and seat position using two-wire Hall-effect sensors. It is equally suited to any other automotive, industrial, or consumer application using two-wire Hall sensors for position
sensing.

The A6850 is supplied in an industry standard profile 8-pin Pb (lead) free SOIC package.