Magnetic switch with integrated ASIL-B self-test for auto-driving cars

Functional safety applications such as automated driving are the target of a pair of Hall sensors from Allegro MicroSystems.

They are pin-compatible upgrades for existing three-wire Hall switch and latch ICs, developed in accordance with ISO 26262:2011 with ASIL-B capability (pending assessment).

Self-test features are integrated, that are always active in the background while the system is running. This action is automatic, and the tests are executed quickly (25µs typical) and so are transparent to host system “even in the case of latches used in high-speed motors and encoders”, said the firm.

Diagnostics Coverage

Hall plate connectivity and biasing
Signal path and Schmitt trigger
Regulator voltage for normal operation
Digital subsystem and non-volatile memory
Over-temperature and single point failures redundancy
Output verified through valid regulations states (external monitor)

A voltage-mode output communicates the sensor’s status (including the safe state), while remaining backward compatible with logic-level interfaces, application circuits, wiring, and firmware.

Output voltage

90-100% fault indicated
70-90% normal logic high
30-70% fault indicated
10-30% normal logic low
0-10% fault indicated

“Our challenge was to achieve the safety level required by present and future ADAS systems while being backward-compatible with our installed base of billions of Hall switches and latches,” said Allegro product line director Jim Judkins. “The result is the fastest diagnostics available for magnetic switches and latches and a logic-compatible output that can communicate the sensor status and support wiring open/short detection.”

The APS11450/12450 are qualified beyond the requirements of AEC-Q100 grade 0. They were developed to ISO 26262 as a hardware safety element out of context with ASIL-B capability (pending assessment). In other safety systems, “using the APS11450/12450 devices, an ASIL-B (or higher) rating can be achieved without redundant sensors”, according to Allegro.

Two packages are available: LH package is a SOT-23W style package for surface-mount, UA is a 3pin, single in-line package for through-hole. Both are Pb-free.

Magnetic characteristics are matched to legacy Hall sensors – each has three sensitivity magnetic options, and versions are available with different thermal characteristics to match the temperature drifts of SmCo, NdFeB, or ferrite magnets.

Operation is over 3.3 to 24V, with sustained 175°C junction temperature, surviving +35V and -30V (reverse-battery), output shorts, load-dump, and some other over-voltage transients.

Applications are expected in driver assistance systems (ADAS), encoders for window lifts, seat motors, seatbelt tensioners, seatbelt closures, human machine interfaces, roll-over (bank angle) sensors and two-wheeler kickstands.