A two-wire, Hall-effect latch from Allegro MicroSystems Europe, the A1244, has on-chip transient protection and a zener clamp to protect against over-voltage conditions on the supply line. The device uses the same patented high-frequency, four-phase, chopper-stabilisation technique that is used on the company's complementary unipolar switches. This is claimed to result in lower noise on the output, less switch-point variation over temperature, and faster settling times. In automotive transmission position sensing systems, two-wire latches require one less wire for operation compared with the more traditional open-collector output latches. The user also gains diagnostic capabilities, because there is always current flowing at one of two specified levels. Any output current outside these two narrow ranges is a fault condition.
