DMOS microstepping driver with translator and overcurrent protection

March 24, 2016 // By Graham Prophet
With a simple STEP/DIR interface to make microstepping straightforward and accurate, this integrated bipolar stepper motor driver IC has a built-in translator. Allegro’s A5984 is designed to operate 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 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 easy implementation of the A5984. Simply 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 A5984 interface is suitable for 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, under voltage lockout (UVLO), and crossover-current protection. Special power-on sequencing is not required.


The A5984 is supplied in three surface mount packages: two QFN packages - the 4 × 4 mm, 0.75 mm nominal overall height ES package and a 5 × 5 mm × 0.90 mm ET package. It is also available in a 24-pin TSSOP LP package. All three packages have exposed pads for enhanced thermal dissipation. The ET package meets customer requirements for no smoke no fire (NSNF) designs by adding no-connect pins between critical output, sense, and supply pins. In the case of a pin-to-adjacent-pin short, the device does not cause smoke or fire. Additionally, the