The A3977 from Allegro MicroSystems is a stepper-motor driver IC with a built-in translator circuit for easy operation of microstepping functions. With this device, it is only necessary to input one pulse on the step input for the motor to take one microstep. No phase sequence tables, high-frequency control lines or complex interfaces to program are required.
The integration of the microstepping control functions means that the A3977 can run independently of a microprocessor, making it ideally suited to applications where complex processors are unavailable or over-burdened.
This IC is designed to operate bipolar stepper motors in full, half, quarter and eighth step modes, with output drive capability of 35 V and ±2,5 A. It includes a fixed off-time current regulator that has the ability to operate in slow, fast or mixed-decay modes, automatically selected by the chopping control.
When a 'step' signal occurs, the A3977 determines if that step results in a higher or lower current in each of the motor phases. If the change is a higher current, the decay mode is set to slow decay. If the change is a lower current, the voltage at the 'percentage fast decay' input will set the decay mode. 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-modulated (PWM) operation. Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout (UVLO) and crossover current protection. Special power-up sequencing is not required.
Applications for the A3977 include the office automation, industrial and medical markets. The inclusion of a 'sleep' mode, coupled with a 3,3-5 V logic supply voltage range, makes the A3977 ideally suited to use in battery-powered equipment.
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