DMOS microstepping driver with translator simplifies design-in

July 13, 2016 // By Graham Prophet
Allegro MicroSystems’ A5985 is an integrated bipolar stepper motor driver IC with built-in translator; a proprietary current control method maximises microstepping accuracy .

The IC operates bipolar stepper motors from full-step up to 1/32 step modes that are selectable by MSx logic inputs. This device has an output drive capacity of up to 40V and ±2A and operates with a single supply. It is targeted at the office and industrial automation markets with key applications to include: automatic teller machines, point of sale and laser printers, 3D printers, copiers, CCTV cameras, sewing machines, vending, and robotics.


The A5985 motor driver IC introduces a proprietary Adaptive Percent Fast Decay (APFD) algorithm to optimise the current waveform over a wide range of stepper speeds and stepper motor characteristics. APFD adjusts, on-the-fly, the amount of fast decay with the goal of maintaining current regulation while minimising current ripple. This adaptive feature improves performance of the system resulting in reduced audible motor noise, reduced vibration, and increased step accuracy. The translator is the key to the simple implementation of the A5985. Inputting one pulse on the STEP input drives the motor one microstep. There are no phase sequence tables, high frequency control lines, or complex interfaces to program. The A5985 interface suits applications where a complex microprocessor is unavailable or is overburdened.


Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation. Internal circuit protection included: Overcurrent protection for motor lead short to ground or supply, thermal shutdown with hysteresis, undervoltage lockout (UVLO), and crossover-current protection. Special power-on sequencing is not required.


The A5985 is supplied in a 28-pin, 5 × 5 × 0.90 mm QFN package (ET designator) with exposed pad for enhanced thermal dissipation. Its data sheet is here.


Allegro Microsystems;