Automotive Hall-effect switch offers self-diagnostics for SIL

January 08, 2014 // By Graham Prophet
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.

It is the only Hall sensor IC capable of verifying proper electrical performance and magnetic sensing: a critical feature for safety applications that must adhere to Automotive Safety Integrity Level standards or 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 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 (pulse-width modulated) 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. This can eliminate the need for redundant sensors in safety-critical applications and satisfies most Automotive Safety Integrity Level requirements.

The device offers superior temperature stability through the use of 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 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. Data sheet here.

Allegro Microsystems; www.allegromicro.com