基于A4936设计的三相无刷DC马达驱动技术

A4936是Allegromicro公司的完整的三相无刷DC（BLDC）马达预驱动器，提供高达28V的输出，直接用来驱动六个功率N-MOSFET的大电流栅极。骑虎难下包括三个霍尔器件输入，用于换相控制的顺序器，PWM电流控制以及同步转子检测。本文介绍了A4936主要特性和优势，功能方框图和典型应用框图。

The A4936 is a complete 3-phase brushless DC motor pre-driver, supplying up to 28 V output for direct, high-current gate drive of an all N-channel power MOSFET 3-phase bridge. The device has 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. Locked rotor detection delay is set by an external capacitor on the CLD terminal. The PWM, DIR, and BRAKE and STOP inputs can be used to control motor speed, position, and torque. Motor speed can be determined using the FG output from an FG coil amplifier and comparator.

The external MOSFETS can be PWMed using an external signal on the PWM input, or using the internal PWM current regulator. In either case, the A4936 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 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. Operating temperature range is –20℃ to 105℃.

The device package is a 32-contact, 5 mm × 5 mm, 0.90 mm nominal overall height QFN, with exposed pad for enhanced thermal dissipation. This small-footprint package is lead (Pb) free, with 100% matte tin leadframe plating.

A4936主要特性和优势：

• Drives 6 N-channel MOSFETs

• Synchronous rectification for low power dissipation

• Internal UVLO and thermal shutdown circuitry

• Hall element inputs

• PWM current limiting

• Dead time protection

• FG outputs

• Standby mode

• Lock detect protection

• Overvoltage protection

图1。A4936功能方框图

图2。A4936典型应用框图