Allegro Bipolar Stepper Motor Driver A3987

DMOS Microstepping Driver with Translator


Top Features

  • Low RDS(on) outputs
  • Short-to-ground protection
  • Shorted load protection
  • Automatic current decay mode detection/selection
  • Mixed and slow current decay modes
  • Synchronous rectification for low power dissipation
  • Internal UVLO and thermal shutdown circuitry
  • Crossover-current protection


The A3987 is a complete microstepping motor driver with built-in translator for easy operation. It is designed to operate bipolar stepper motors in full, half, quarter, and sixteenth step modes, with output drive capability of 50 V and 1.5 A. The A3987 includes 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 A3987. Simply inputting one pulse on the step input drives the motor to take one microstep. There are no phase sequence tables, high frequency control lines, or complex interfaces to program. The A3987 interface is an ideal fit for applications where a complex microprocessor is unavailable or over-burdened.

The A3987 chopping control automatically selects the current decay mode (slow or mixed). When a STEP signal occurs, the translator 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 decay mode is set to 30.1% fast decay. 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), and crossover current protection. Special power-up sequencing is not required.

The A3987 is supplied in a thin profile (1.2 mm maximum height) 24-lead TSSOP (suffix LP) with exposed thermal tab. The package is lead (Pb) free with 100% matte tin leadframe plating.


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