Low-voltage stepper motor driver IC from Allegro

The new device - part of Allegro’s low voltage motor driver series targeted at portable battery-powered applications in the consumer, industrial, office automation and medical markets - has output channels rated at 1 A each and an operating supply voltage range of 2.5 V to 9 V. Key features include fixed off-time PWM (pulse-width modulated) current control, low ‘on’ resistance DMOS outputs and a peak current flag output.

The output current for each full bridge circuit can be controlled using the internal fixed off-time PWM regulator or by PWM control of the two logic inputs. The current flag output, which 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, is triggered when the output current reaches the trip level for the internal PWM regulator, and stays on for a minimum of 300 μs.

The output drivers are all N-channel DMOS full bridges. An internal charge pump supply will double or even triple the back bias voltage to ensure proper gate drive voltage for the high and low side DMOS devices. The resulting stable gate drive results in a consistent output ‘on’ resistance over the full input voltage range.

Protection features include thermal shutdown, undervoltage lockout and crossover current protection. Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation.

The A3906 is supplied in a 4 mm x 4 mm, 20-contact QFN package with exposed thermal pad. This small footprint package is lead (Pb) free with 100% matte tin leadframe plating.