基于A4936設計的三相無刷DC馬達驅動技術
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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主要特性和優勢：
? 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
圖1。A4936功能方框圖
圖2。A4936典型應用框圖
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