Power Electronics

Switching into Ultra-Slim MLP Packages

Responding to feedback from users, Allegro MicroSystems Inc. has made enhancements to its existing micropower omnipolar Hall-effect switch A3212, which was released almost 18 months ago. The new additions to this line of pole independent, ultra-sensitive switch with latched digital output, A3213 and A3214, come in ultra-slim micro lead-frame package (MLP) with a height of only 0.75 mm. Its length is 2 mm, and the width of the MLP package is 3 mm (Fig.1). According to product marketing manager Josh Bailey, this is the first Hall-Effect device to be offered in an ultra-slim MLP package.

Other improvements include higher voltage range, extended temperature, and slightly wider switch points. While the older A3212 is designed for operation between 2.5V to 3.5V, the A3213 and A3214 can operate from battery voltages of 2.4V to 5.5V — ideal for use in almost all handheld portable electronic equipment. They have nominal current consumption of 300µA and 5µA, respectively. Additional features include chopper-stabilization for improved stability, high-sensitivity thresholds, temperature stability, low switch-point drift, and insensitivity to physical stresses.

These low-power omnipolar parts incorporate a clocking scheme designed to reduce the average operating power requirements, making them suited for the detection of open/closed positions in battery-operated equipment. The patented omnipolar feature simplifies application assembly by allowing the device to detect the presence or absence of a magnetic field irrespective of the magnet's polarity.

The internal clocking scheme activates the sensor for 60µs and deactivates it for the remainder of the period. A short awake time allows for stabilization prior to sensor sampling and data latching on the falling edge of the timing pulse. On average, the A3212 and A3214 look for a change in magnetic flux every 60 ms. If the change is above the operate point of the part, the device latches on. If the change is below the release point of the part, the device latches off. As a result of this clocking scheme, the Hall-effect switches are able to reduce the average supply current to around 5uA.

However, unlike others, A3213 uses a faster clock period of 240µs. This is ideal for programs that need to detect faster moving objects or systems that need quicker response time from the sensor, said Bailey. Like A3212 and A3214, the awake time is again 60µs for A3213. The result of the faster period is 300uA of supply current. But, added Bailey, it‘s still a tremendous reduction from the standard Hall sensor, which has about 5mA supply current.

According to Allegro MicroSystems, the polarity independence and minimal power requirements enable these switches to replace reed switches for high reliability and ease of manufacturing, while eliminating the need for signal conditioning, Implemented in 1.25µm biCMOS process, these devices include on a single chip a Hall-voltage generator, small signal amplifier, chopper stabilization, a latch, and a MOSFET output (Fig.2). The temperature capability of the new Hall-effect switches has been extended to 150°C, making them suitable for automotive and other harsh industrial environments. Thus, the operating temperature range for A3213 and A3214 is -40°C to +150°C.

Besides the ultra-slim MLP package, the two new devices also come in single-in-line (SIP) and surface-mount SOT23W packages. The A3213 and A3214 are each priced at $0.50, in quantities of 10,000.

For more information, visit www.allegromicro.com or CIRCLE 349 on Reader Service Card

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