Tuesday 20 December 2011

Two-wire Hall-effect latch

The A1244 from Allegro Microsystems,  is a two-wire Hall-effect latch featuring on-chip transient protection and a zener clamp to protect against overvoltage conditions on the supply line.

The new device, which is programmed at the factory to optimise the magnetic switch point accuracy, uses the same patented high-frequency, 4-phase, chopper-stabilisation technique that is used on the company's complementary family of unipolar switches. This results in lower noise on the output, less switch-point variation over temperature, and faster settling times.

The improvement in noise and switch-point drift allows the device to realise much better switching accuracy, which means better switching repeatability. Moreover, the improved high-voltage transient protection allows the A1244 to survive the conditions specified in ISO 7637-2 and 40 V load dump.
Allegro's advanced BiCMOS wafer fabrication process is used to achieve magnetic stability over temperature and to eliminate the offset inherent in single-element devices when exposed to harsh application environments.

Two-wire latches are particularly advantageous in cost-sensitive applications, such as automotive transmission position sensing and motor commutations applications, because they require one less wire for operation compared with the more traditional open-collector output latches. In addition, the user inherently 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.

The A1244 is available in two package styles: the "LH" is a SOT-23W style, miniature low-profile package for surface-mount applications, and the "UA" is a TO-92 style, three-lead ultra-miniature single inline package (SIP) for through-hole mounting. The A1244 is also offered with two supply-current options: -I1 from 5.0 to 6.9 mA, and  -I2 from 2.0 to 5.0 mA.

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