DMOS Motor Driver ICs For Office Automation Market

Allegro Microsystems Europe has introduced four DMOS microstepping motor driver ICs for the office automation market. The new A4982, A4984, A4985 and A4988 devices feature built-in over-current protection, simple 'step' and 'direction' interfaces and built-in translators. The integrated devices require few external components and occupy a small footprint in a compact, thermally efficient package, according to the company. The new devices are designed to operate bipolar stepper motors in full, half, quarter, eighth and sixteenth step modes, with an output drive capacity of up to 35V and +/-2A.

They include a fixed off-time current regulator, which can operate in slow or mixed decay modes. The built-in translator facilitates the implementation of the devices; simply inputting one pulse on the 'step' input is said to drive the motor one microstep. There are no phase sequence tables, high-frequency control lines or complex interfaces to program. The interface is suitable for applications where a complex microprocessor is unavailable or overburdened.

The chopping control circuitry automatically selects the current decay mode (slow or mixed). When a signal occurs at the 'step' input pin, the device determines if that step results in a higher or lower current in each of the motor phases. If the change is to a higher current, the decay mode is set to slow decay. If the change is to a lower current, the current decay is set to mixed.

In this mode, the current is set initially to a fast decay for a period amounting to 31.25 per cent of the fixed 'off' time, then to a slow decay for the remainder of the 'off' time. According to Allegro Microsystems, this current decay control scheme results in reduced audible motor noise, increased step accuracy and reduced power dissipation. Internal synchronous rectification control circuitry is provided to improve power dissipation during pulse-width-modulation operation.

Internal circuit protection includes thermal shutdown with hysteresis, under-voltage lockout, crossover current and over-current protection. Special power-on sequencing is not required. The A4982, A4984, A4985 and A4988 devices are offered in several different package options: 28- and 32-contact 5 x 5 x 0.90 mm QFN (ET) packages; a 24-contact 4.0 x 4.0 x 0.75mm QFN (ES) package; and a 24-lead 7.8 x 4.4 x 1.2mm eTSSOP (LP) package. All packages feature exposed thermal pads for enhanced thermal dissipation and are lead free, with 100 per cent matt tin-plated lead frames.

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