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issue: December 2005 APPLIANCE Magazine

Motor Technology
Full-Bridge Motor Driver

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A new full-bridge motor driver is designed to drive single-phase, low-voltage, bipolar brushless DC (BLDC) motors.

Gary T. Pepka, strategic marketing manager - Sensors, NAM, Allegro MicroSystems, Inc. (Worcester, Massachusetts, U.S.) tells APPLIANCE that the company sees a constant pressure to reduce motor size and add functionality and reliability in cell phones and other applications. The A1441 full-bridge motor driver targeted the requirements.

Commutation of the motor is achieved using a single Hall element to detect the position of an alternating pole ring magnet. The supplier of the A1441 motor driver, Allegro MicroSystems, Inc. (Worcester, Massachusetts, U.S.), says its advanced IC semiconductor process allows for the integration of the Hall element on the same integrated circuit (IC) as the motor control circuitry, providing a single-chip solution. Allegro says it is one of just two suppliers in the world that integrate a full bridge motor driver and a Hall element for commutation. The advantage of a single-chip solution for a motor driver comes through the conservation of board space through reduction of discrete components.
“Many coin-type vibration motors are no larger than 0.70 cm in diameter, thus printed circuit board space is at a premium,” Gary T. Pepka, strategic marketing manager-Sensors, NAM, tells APPLIANCE.
Circuit board space is also optimized with the use of an on-chip charge pump circuit, which allows for the use of a MOS full-bridge output, complete with body diodes, and eliminating the need for flyback diodes or capacitors. All necessary circuitry is integrated and no external devices are required. Allegro recommends a bypass capacitor to lower switching transients and, therefore, reduced radiated emissions. The switchpoints of the device are chopper-stabilized for precision over operating temperature and voltage.
“Focus applications for the A1441 include vibration motors for cellular phones and pagers and other energy conscious, battery-powered applications, which may use small, 100 mH 2-phase DC motors,” Pepka says.
An active braking function and sleep mode are also key features of the motor driver. “The sleep mode causes the device to be inactive and hence draw less current,” Pepka tells APPLIANCE. “This is important for sustaining battery life, because this feature allows a microprocessor to keep the device in sleep mode during periods when the vibration motor is not needed.”
The braking function, he adds, allows the motor to be turned on and off more quickly. “Much like vibrating video game controllers, this function gives new game phones more ‘feel’ during play,” he says.
The device, targeted at the consumer products market, is available in a low-profile 2-mm by 2-mm by 0.5-mm MLP package with 100-percent tin plating.

Suppliers mentioned in this article:
Allegro MicroSystems Inc.

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