Motor driver shrinks without thermal compromise

A DMOS full-bridge motor driver integrated circuit controls the speed, direction of rotation and torque of a DC motor with externally applied PWM control signals.

The new A3950 from Allegro MicroSystems Europe is a DMOS full-bridge motor driver integrated circuit for controlling the speed, direction of rotation and torque of a DC motor with externally applied PWM (pulsewidth-modulated) control signals.

Key features of the new device include synchronous rectification, overcurrent protection, low-on-resistance DMOS outputs, a diagnostic output and an exceptionally small package which is less than a quarter of the size of any other equivalent product on the market.

The A3950, which complements Allegro's parallel input DC motor driver family, is capable of peak output currents up to +/-2.8A and operating voltages up to 36V.

The wide operating voltage range reduces the requirement for power-supply regulation and reduces system cost, with no need for a driver logic supply.

Speed, direction and torque are controlled via the device's phase and enable input terminals, while a mode input is also provided to select fast (coast) or slow (brake) PWM current decay control.

Internal synchronous rectification control circuitry reduces power dissipation by switching on the appropriate DMOS outputs to effectively short out the body diodes during PWM operation.

This internal control technique can reduce output power dissipation by 10 to 30% in most applications.

The A3950's overcurrent protection feature prevents damage to the integrated circuit that might occur as a result of short circuits between the motor lead and the supply and ground.

Other internal circuit protection features include thermal shutdown with hysteresis, undervoltage lockout of the motor supply and charge pump output, and crossover current protection.

A diagnostic open-drain output is provided to alert the external system controller to fault conditions such as undervoltage, overtemperature and overcurrent.

The low-on-resistance DMOS outputs result in lower power dissipation: up to 50% lower than other devices on the market.

A sleep mode is also provided to reduces power consumption when the device is not in use.

The A3950 is supplied in a lead-free (Pb-free), 16-lead eTSSOP package with exposed power tab.

The small size of only 5 x 4.4 x 1.2mm makes it the ideal solution when printed circuit board space is limited, and the small size does not compromise the thermal performance, typified by a 34C/W thermal resistance.

Target applications include office equipment, vending and ATM machines, industrial servo drives and medical instrumentation.

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