Programmable unipolar Hall-effect switch comes with inbuilt diagnostics


Unipolar switches, usually known as Unipolar Hall-effect sensor IC’s, are conducted through a positive magnetic field. A single magnet presenting a positive magnetic field of sufficient magnetic flux density causes the device to switch to it’s on. After it has been turned on, the unipolar switches will remain turned on until the magnetic field is removed. On removing magnetic field, switches goes to its OFF state. It has a various application such as in vehicle gear-shift lever for detecting the position of a vehicle, van interrupter switching, proximity sensing, seat positivity sensing, pulse counter, cell-phone flip switch, etc.

Allegro Microsystems has recently cultivated a new unipolar hall-effect switch with an apparently authorized diagnostic function and user programmable switch points. (Allegro Microsystems LLC private company is a leader in constructing, manufacturing and marketing high-performance semiconductors). They have created A1162 with on-chip electromagnetic coils. It is used to perform self-test of the whole magnetic and electrical signal chain of the sensor.

The purpose of designing the A1162 for systems is by considering some critical factors like exact magnetic switch points, safety, reliability, or both to meet the requirements of ISO 26262.

ISO 26262 is an international standard for functional safety of electrical and electronic systems in production automobiles defined by the International Organization for standardization in 2011. It is a derivative of IEC61508.

The A1162 has functions like a standard Unipolar Hall-effect switch in its normal operating mode. The output transistor of A1162 turns on in the presence of sufficient magnetic field (output signal switches low > maximum BOP). Similarly, the output transistor of A1162 turns off when the magnetic field is removed (output signal switches high < minimum BRP). Its applications are in including shift selectors (PRNDL), seat belt buckles and brake sensors.

When the diagnostic feature of A1162 is activated, its output becomes as a square wave. It proves that the device is sensing inside generated magnetic field properly. The result comes out as it increases robustness in safety-critical applications that may need redundant sensors. It eliminates the need for redundant sensors in safety critical applications.

This massive IC merges voltage regular, half voltage generator, small signal amplifier, chopper stabilization, Schmitt trigger and short- circuit- protected- open- collector output (capable to full in up to 25MA). The onboard regulator allows operation of 3.8 to 24V supply voltages.

Due to advanced dynamic cancellation techniques, high-temperature performance is possible. It is capable of reducing residual offset voltage, which is caused due to device overloading, temperature dependencies, and thermal stress. The adjacency of the coils to the Hall sensing element permits the element to sense the field while ignoring external fields. When the device is properly sensing inside a magnetic field, it gives output a PWM signal of %0% duty cycle, in diagnostic mode.

The operating temperature range of A1160 is -40 degrees C to +150 degree C. It is supplied in a small surface mount, % lead (SOT 23W) package. The device works on the whole electrical signal path of the integrated circuit.