A3906 Low Voltage Stepper and Single/Dual DC Motor Driver


A3906 is a low-voltage, dual, full-bridge motor driver designed to drive 1 bipolar stepper motor or 2 DC motors. Each output channel in this new device is rated at 1 A with an operating supply voltage range of 2.5 to 9V. Key features include fixed off-time PWM current control, low-on-resistance DMOS outputs, and a peak current flag output.


The output current for each full bridge can be controlled using the internal fixed-off-time PWM regulator or by PWM control of the two logic inputs. The current flag output is triggered when the output current reaches the trip level for the internal PWM regulator and stays on for a minimum of 300 µs. This feature is used to detect DC motor stall conditions and allows for control of the stall time for improved battery life and to prevent damage to the motor.


The output drivers are all N-channel DMOS full bridges. An internal charge pump supply will double or even triple VBB to ensure proper gate drive voltage for the high and low side DMOS. The stable gate drive results in a consistent output on-resistance over the full input voltage range. Protection features include thermal shutdown, under voltage lockout, and crossover current protection. Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation.


Allegro’s A3906 is targeted at the consumer, industrial, office automation, and medical markets and is supplied in a 4 x 4 mm, 20-contact QFN package with an exposed thermal pad. This small footprint package is lead (Pb) free with 100% matte tin lead frame plating.


  • 2.5 to 9V operation
  • Internal PWM current limit control
  • Synchronous rectification for reduced power dissipation
  • Peak current output flag
  • Undervoltage lockout
  • Low RDS(on) outputs
  • Small package
  • Brake mode for DC motors
  • Sleep function
  • Crossover-current protection
  • Thermal shutdown
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