Allegro MicroSystems, Inc. (www.allegromicro.com) unveiled the expanded microstepping motor driver line, including four new devices which utilize a simple Direction and STEP interface and require fewer external components. The company’s A4988/A4985/A4984 and A4982 devices are complete microstepping motor drivers with an embedded translator for overcurrent protection and easy operation to reduce rework cost in both normal and manufacturing operations.
These new devices are made to operate bipolar stepper motors in sixteenth, eighth, quarter-, half- and full- step modes, with output drive capacity of up to ±2A and 35V. These devices include a fixed off-time current regulator, which can operate in Mixed or Slow decay modes. The translator is the key to implement devices easily. Simply inputting a single pulse on the STEP input drives the motor one microstep. There are no complex interfaces, phase sequence tables or high frequency control lines to program. The interface is best suited for applications where a complex microprocessor is overburdened or is unavailable.
The chopping control automatically chooses the current decay mode (“Slow or Mixed”). Once a signal occurs at the STEP input pin, the devices determine if that step results in a lower or higher current in every motor phase. If it changes to a higher current, the current decay is set to Slow decay. If it changes to a lower current, the decay mode is set to Mixed (“set initially to a fast decay for a period amounting to 31.25 percent of the fixed offtime, then to a slow decay for the remainder of the off-time”). The current decay control scheme results in increased step accuracy, reduced power dissipation and reduced audible motor noise.
To improve power dissipation in PWM operation, an internal synchronous rectification control circuitry is provided. This internal circuit protection includes: over-current protection, crossovercurrent, undervoltage lockout (UVLO) and thermal shutdown with hysteresis.