Wednesday 21 April 2010

Protection against voltage transients & high temps

Hall-effect latches withstand high-voltage transients and high temperatures

The new A1225, A1227 and A1229 from Allegro MicroSystems Europe are a family of Hall-effect latch ICs that combine enhanced protection against high transient voltages with the ability to operate over extended temperature ranges up to +150°C.

These extremely temperature-stable and stress-resistant sensor ICs are especially suited for applications that require high-voltage transient protection close to the sensors, but where space or distance considerations preclude the use of external protection devices. Typical uses include motor commutation in sunroofs and power windows within the automotive market.

The A1225/7/9 devices include Allegro’s advanced offset cancellation technique which, along with high-speed 4-phase chopping, gives lower noise on the output, less switch-point variation with temperature, and faster settling times. The resulting improvements in noise and switch-point drift lead to much better switching accuracy and repeatability.

Superior high-temperature performance is made possible through a Schmitt trigger circuit that maintains operate and release point symmetry by compensating for temperature changes in the Hall element. In addition, the internal compensation circuitry provides magnetic switch points that become more sensitive with temperature, hence offsetting the usual degradation of the magnetic field with temperature. The symmetry capability makes these devices ideal for use in pulse-counting applications where duty cycle is an important parameter.

The improved high-voltage transient protection allows the devices to survive the tests specified in ISO 7637-2 and a 40 V load dump for less than 0.5 s with minimal external protection. In addition, enhanced ESD (electrostatic discharge) prevention structures provide ESD protection of up to 8 kV HBM (human body model) without the need for external protection components.
The three basic devices (A1225, A1227 and A1229) are identical except for magnetic switch points. Each device includes, on a single silicon chip, a voltage regulator, Hall-voltage generator, temperature compensation circuit, signal amplifier, Schmitt trigger, and a buffered open-drain output to sink up to 25 mA. The on-board regulator permits operation with supply voltages of 3.8 V to 24 V.

The first character of the part number suffix determines the device operating temperature range, with suffix ” L” denoting -40°C to +150°C. Two package styles provide a magnetically optimised package for most applications. Suffix “LT” is a miniature SOT89/TO-243AA transistor package for surface-mount applications, while suffix “UA” is a 3-lead ultra-miniature single-inline package. Both packages are lead (Pb) free with 100% matt tin leadframe plating.

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