A3981: Automotive, Programmable Stepper Driver


The A3981 is a flexible microstepping motor driver with built-in translator for easy operation. It is a single-chip solution, designed to operate bipolar stepper motors in full-, half-, quarter- and sixteenth-step modes, at up to 28 V and ±1.4 A. The A3981 can be controlled by simple Step and Direction inputs, or through the SPI-compatible serial interface that also can be used to program many of the integrated features and to read diagnostic information.

The current regulator can be programmed to operate in fixed off-time or fixed frequency PWM, with several decay modes to reduce audible motor noise and increase step accuracy. In addition the phase current tables can be programmed via the serial interface to create unique microstep current profiles to further improve motor performance for specific applications.

The current in each phase of the motor is controlled through a DMOS full bridge, using synchronous rectification to improve power dissipation. Internal circuits and timers prevent cross-conduction and shoot-through, when switching between high-side and low-side drives.

The outputs are protected from short circuits, and features for low load current and stalled rotor detection are included. Chip-level protection includes: hot and cold thermal warnings, overtemperature shutdown, and overvoltage and undervoltage lockout.


  • Automotive stepper motors
  • Engine management
  • Headlamp positioning

Top Features

  • Peak motor current up to ±1.4 A, 28 V
  • Low RDS(on) outputs, 0.5 Ω source and sink, typical
  • Automatic current decay mode detection/selection
  • Mixed, Fast, and Slow current decay modes
  • Synchronous rectification for low power dissipation
  • Internal OVLO, UVLO, and Thermal Shutdown circuitry
  • Crossover-current protection
  • Short circuit and open load diagnostics
  • Hot and cold thermal warning
  • Stall detect features
  • SPI-compatible or simple Step and Direction motion control
  • Highly configurable via SPI-compatible serial interface

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
A3981KLP-T 28-lead TSSOP -40°C to 125°C Yes View Data Contact your
local sales rep
Distributor Stock
A3981KLPTR-T 28-lead TSSOP -40°C to 125°C Yes View Data Contact your
local sales rep
Distributor Stock
APEK3981KLP-01-T DEMO BOARD -40°C to 125°C No -- Contact your
local sales rep
Distributor Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.


The A3981 is supplied in a 28-pin TSSOP power package with an exposed thermal pad (package type LP). This package is lead (Pb) free with 100% matte tin leadframe plating.

LP TSSOP 28 pin

Design Support Tools

When ordering an APEK3981KLP-01-T demo board, please remember to order all three part numbers:

Part Numbers  
APEK3981KLP-01-T Demo Board
A3981KLP-T Sample Parts