Unipolar Hall switch supports automotive safety requirements

January 08, 2014 // By Christoph Hammerschmidt
The A1160 from Allegro MicroSystems Europe is a unipolar Hall-effect switch with built-in diagnostic capabilities that provide a solution to the monitoring of device performance and the self-diagnosis of incorrect device operation.

The device is - according to the vendor - currently the only Hall sensor IC capable of verifying proper electrical performance and magnetic sensing - which is considered a critical feature for safety applications that must adhere to Automotive Safety Integrity Level standards. The same holds true for those applications requiring two sensors for redundancy.

The key to the self-diagnostic capability of the A1160 is an integrated coil surrounding the Hall sensing element. During normal operation, the A1160 functions as a typical unipolar switch (with the output turning on in the presence of a south-pole magnetic field and turning off when the field is removed), but when the diagnostics pin is pulled high it enters the diagnostics mode.

This feature allows current to pass through the integrated coils, generating a magnetic field. The proximity of the coils to the Hall sensing element allows the element to sense the field generated by the coil, while ignoring external fields. In diagnostics mode the device will output a PWM signal of 50% duty cycle when the device is properly sensing the internally generated magnetic field.

The diagnostics mode exercises the entire electrical signal path of the integrated circuit, and ensures proper sensing of the magnetic signal to provide accurate device functionality.

The A1160 eliminates the need for redundant sensors in safety-critical applications and satisfies most Automotive Safety Integrity Level (ASIL) requirements.

The device offers superior temperature stability through the use of advanced chopper stabilisation techniques. It includes output short-circuit protection and reverse battery protection, as well as an internal regulator which enables operation from unregulated supplies.

The Allegro A1160LLH-T is targeted at both the automotive and industrial markets. It has an operating temperature range of -40°C to +150°C and is supplied in a small surface-mount 5-lead (SOT-23W) package.

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