April 29, 2010
Worcester, MA – Allegro MicroSystems, Inc. announces the expansion of their microstepping motor driver line to include four new devices that require fewer external components and utilize a simple STEP and Direction interface. Allegro’s A4982/A4984/A4985 and A4988 devices are complete microstepping motor drivers with a built-in translator for easy operation and overcurrent protection to reduce the rework cost in both manufacturing and normal operations. They are targeted at the office automation market.
These latest 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 35 V and ±2 A. They include a fixed off-time current regulator which has the ability to operate in Slow or Mixed decay modes. The translator is the key to the easy implementation of the devices. Simply inputting one pulse on the STEP input drives the motor one microstep. There are no phase sequence tables, high frequency control lines, or complex interfaces to program. The interface is an ideal fit for applications where a complex microprocessor is unavailable or is overburdened.
The chopping control 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, then the decay mode is set to Slow decay. If the change is to a lower current, then the current decay is set to Mixed (set initially to a fast decay for a period amounting to 31.25% of the fixed offtime, then to a slow decay for the remainder of the off-time). 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 PWM operation. Internal circuit protection includes: thermal shutdown with hysteresis, undervoltage lockout (UVLO), crossovercurrent, and over-current protection. Special power-on sequencing is not required.
Allegro’s A4982/A4984/A4985 and A4988 are offered in several different package options: a 28 and 32 contact 5 mm × 5 mm × 0.90 mm QFN (ET) package, a 24 contact 4.0 mm × 4.0 mm × 0.75 mm QFN (ES) package, and a 24 lead 7.8 mm × 4.4 mm × 1.2 mm eTSSOP (LP) package. All packages have exposed thermal pads for enhanced thermal dissipation, and are lead (PB) free with 100% matte tin plated lead frames.