Monday 21 June 2010

DC motor pre driver IC

The new A4936 from Allegro MicroSystems Europe is a three-phase brushless DC motor pre-driver IC targeted at applications within the office automation sector including laser printer and copier drum drives.

The new device incorporates outputs for the direct high-current gate drive of an all N-channel power MOSFET three-phase bridge with a maximum supply voltage of 38 V. Also included in the A4936 device are three Hall-element inputs, a sequencer for commutation control, fixed off-time pulse width modulation (PWM) current control, and locked-rotor detection.

Output current is scaled by the capability of the external MOSFETs, and locked-rotor detection delay is set by an external capacitor on the CLD terminal. The PWM, DIR, BRAKE and STOP inputs can be used to control motor speed, position, and torque. The motor speed can be determined using the motor's FG (frequency generator) coil signal, which is amplified and shaped with the internal differential amplifier and comparator to produce a digital FG signal output.

The external MOSFETs can be pulse-width-modulated by using an external signal on the PWM input or the internal PWM current regulator. In either case, the synchronous rectification capability of the A4936 reduces power dissipation by turning on the appropriate MOSFETs during current decay.

The Hall elements can be inexpensive types, and are used in conjunction 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, undervoltage lockout and dead-time protection. Special power-up sequencing is not required. The operating temperature range is -20°C to +105°C.

The A4936 is supplied in a 5 x 5 mm, 32-terminal QFN package with exposed thermal pad. This small footprint package is lead (Pb) free with 100% matt tin leadframe plating.

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