Integrated circuit drives DC fans, blowers and pumps

Paul Boughton
The A4930 from Allegro Microsystems Europe is a single-phase brushless DC motor pre-driver integrated circuit for controlling high-current devices such as fans, blowers or pumps with supply voltages from 8-36V.

Key features include PWM (pulse width modulated) current control, locked-rotor protection with auto restart, outputs to drive an all N-channel Mosfet H-bridge, a minimal requirement for external components, and programmable commutation delay, soft start and minimum speed.

The motor speed is regulated by either a PWM input or an external analogue voltage – typically from a thermistor. The speed can be monitored via the device's FG (fan gain) output, and minimum speed is programmed with an external voltage.

Maximum motor current is controlled with the internal PWM fixed off-time current regulator. Synchronous rectification is employed in the PWM 'off' cycle to reduce power dissipation. Start-up current can be ramped up for reduced supply current surges, and lock detection with automatic restart functions reduces damage due to motor overheating.

A single resistor is used to program the commutation delay to prevent shoot-through and to reduce fan noise. An internal 5V regulator is provided for the Hall element.

Protection features include thermal shutdown with hysteresis, undervoltage lockout (UVLO), crossover current and locked-rotor protection with auto restart. Special power-up sequencing is not required.

The new device is targeted at the office automation, telecommunications, consumer and industrial markets. It is supplied in a lead-free 28-pin QFN package (suffix ET) with exposed power tab. It has a 5 x 5mm footprint and 0.90mm nominal height.

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