Analysis

Linear Hall-effect sensors have a user-selectable 'sleep' mode

26th February 2008
ES Admin
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The A139x family of linear Hall effect sensor integrated circuits from Allegro MicroSystems Europe combines micropower operation, a tri-state output and a user-selectable 'sleep' mode. The new sensor ICs provide a voltage output that is directly proportional to an applied magnetic field. The 'sleep' mode allows the devices to operate at a current consumption of less than 25 µA, which contrasts with typical Hall-effect ICs whose sensitivity before amplification is directly proportional to the current flowing through the transducer element. As a result, it is difficult to achieve sufficient sensitivity levels with traditional Hall-effect sensor ICs without consuming more than 3 mA of current.
This low-current operation and the resulting power consumption of less than 10 mW makes these devices perfect for battery-operated applications such as mobile telephones, digital cameras, and portable tools. The operating voltage of 3 V makes them compatible with 2.5-3.5 V supplies.

There are four devices in the family, differentiated only by sensitivity: A1391, 1.25 mV/Gs; A1392, 2.5 mV/Gs; A1393, 5 mV/Gs; and A1395, 10 mV/Gs. Despite the low power consumption of the circuitry in the A139x family, the features required to produce a highly accurate linear Hall effect IC have not been compromised.

Each BiCMOS monolithic circuit integrates a Hall element, improved temperature-compensating circuitry to reduce the intrinsic sensitivity drift of the Hall element, a small-signal high-gain amplifier, and proprietary dynamic offset cancellation circuits. End-of-line post-packaging factory programming allows precise control of device sensitivity and offset.

End users can control the current consumption of the A139x by applying a logic level signal to the 'sleep' pin. The outputs of the devices are not valid during sleep mode, when they switch to high-impedance mode. The high-impedance output feature allows the connection of multiple A139x Hall-effect devices to a single A-to-D convertor input.

The quiescent output voltage of these devices is 50% nominal of the ratiometric supply reference voltage applied to the reference pin of the device.

The new sensors will operate over a wide ambient temperature range from -20°C to +85°C, and feature electrostatic discharge protection of greater than 3 kV.

The A1391x Series devices are available in a small (2.0 × 3.0 mm, 0.75 mm nominal height) microleaded MLP/DFN package. The package is Pb (lead) free, with 100% matt tin leadframe plating.

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