Allegro Introduces New Three-Phase Brushless DC Motor Pre-Driver
Allegro MicroSystems, Inc. introduced a new three-phase brushless dc motor pre-driver targeted at the office automation, telecommunications, consumer and industrial markets. It is designed with outputs for a direct high current gate drive of an all N-channel power MOSFET three phase bridge with a maximum supply voltage of 38V. It also includes Hall element inputs, a sequencer for commutation control, fixed off time pulse width modulation (PWM) current control and locked rotor protection.
Output current is scalable with the choice of external MOSFETS. Enable, Direction and Brake inputs can be used to control the motor, speed, position and torque. Output speed can be regulated using FG1 (once per each Hall transition) and FG2 (once per Hall A transition) outputs. The external MOSFETS can be PWM’d with the Enable input or with the internal PWM current regulator. In both cases Allegro’s A4931 synchronous rectification feature will turn on the appropriate MOSFET(s) during current decay to reduce power dissipation.
The A4931 uses Hall elements with noise filtering to prevent false commutation signals. A 7.5V regulated supply output is provided to power the three Hall elements. Internal circuit protection includes thermal shutdown with hysteresis, under voltage lockout, locked rotor and dead time protection. Special power up sequencing is not required. Operating temperature range is -20 to 105°C.
Allegro’s A4931 is supplied in a 5x5 mm 28 lead QFN package with exposed thermal pad. This small footprint package is lead (Pb) free with 100% matte tin leadframe plating. It is priced at $1.00 in quantities of 1,000 and has a 10-12 week typical lead-time to market.
