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Pre-driver for 3-phase brushless DC motors targets office automation

June 15, 2010

Susan Rambo-June 15, 2010

Worcester, MA -- A new pre-driver integrated circuit for three-phase brushless DC motors is available for office automation products, such as laser printer and copier drum drives. Allegro MicroSystems' A4936 outputs up to 28V for direct, high-current gate drive of an all N-channel power MOSFET three-phase bridge. The A4936 has three Hall-element inputs, a sequencer for commutation control, fixed off-time pulse-width modulation (PWM) current control, and locked-rotor detection.

A4936 drives six N-channel MOSFETs and scales its output current to the external MOSFETs' capability. An external capacitor on the CLD terminal sets the delay on locked rotor detection. PWM, DIR, BRAKE, and STOP inputs can be used to control motor speed, position, and torque. Motor speed can be determined using a motor FG coil signal that is amplified and shaped with the internal differential amplifier and comparator to produce a digital FGS output.

Using an external signal on the PWM input or the internal PWM current regulator, the A4936 can "pulse-width modulate" the external MOSFETS. In either method, says Allegro MicroSystems, the A4936's synchronous rectification feature reduces power dissipation by turning on the appropriate MOSFETs during current decay.

The Hall elements can be inexpensive types when used with internal noise filtering to prevent false commutation signals. The A4936 provides a regulated 7.5 V supply to power the three Hall elements. Internal circuit protection includes thermal shutdown with hysteresis, under voltage lockout, and dead-time protection. Special power-up sequencing is not required. The operating temperature range is -20°C to 105°C. The absolute maximum output is 38V.

Packaging: Lead-free with 100% matte tin lead frame plating, 5mm x 5mm, 32-terminal QFN package with exposed thermal pad. Pricing: $1.00 in quantities of 1,000.

More info on A4936.

(Based on press release.)

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