Proving the Business Case for the Internet of Things

Allegro chip helps detect tampering in smart meters

Steve Rogerson
June 2, 2015
 
To help detect magnetic tampering in smart meters, the A1266 from Allegro MicroSystems is a three-dimensional sensor IC incorporating a combination of vertical and traditional planar Hall-effect sensor ICs that can detect a magnetic field of either polarity in any direction.
 
The omnipolar, omnidirectional sensitivity of the device makes it suitable for detecting magnetic tampering in smart meters, ATMs, gambling and gaming machines, ticket machines and electronic locks. It can also serve as a general-purpose magnetic switch that is virtually insensitive to magnet orientation or polarity in applications such as games, consumer electronics and white goods.
 
This compact surface-mount SOT23 IC is functionally equivalent to an array of three standard Hall-effect sensors mounted in three different orientations: something that is not possible using a single circuit board and all surface-mount components. With a typical BOP operating point of 25G, the device has higher sensitivity than most conventional Hall-effect switches, leading to a claimed high-sensitivity 3D tamper or proximity sensing in less space with lower assembly cost.
 
Each device integrates, on a single silicon chip, three Hall-voltage generators, a small-signal amplifier, chopper stabilisation, a Schmitt trigger, and one or more NMOS outputs. UK-based Allegro’s proprietary dynamic offset cancellation technique means the magnetic operating characteristics are specified across the operating voltage and temperature ranges.
 
The device is for operation in green and battery-powered systems; it can be powered from a 2.5 to 5.0V supply and the average supply current is typically 7.5µA at 2.5V. Operating temperature range is -40 to +85ËšC.
 
Two configurations are available: one with a separate output for each sensing direction (X, Y, Z) and one with a combined output (X+Y+Z). Package type LH is a modified SOT23W surface-mount package that is RoHS-compliant and lead (Pb) free (suffix -T), with a 100 per cent matt-tin plated leadframe.