PWM motor driver controls bipolar microstepping stepper motors

The new device uses a serial interface and includes features such as overcurrent protection, synchronous rectification for low power dissipation, programmable mixed, fast and slow current decay modes, and low 'on' resistance DMOS outputs in a thermally efficient surface-mount package.



The A3992 is capable of continuous output currents up to ±1.5 A and operating voltages up to 50 V. Internal fixed 'off' time PWM current control timing circuitry can be programmed via the serial interface to operate in slow, fast and mixed decay modes.



The desired load current level is set via the serial port with two 6-bit linear digital-analogue convertors in conjunction with a reference voltage. The six bits of control allow maximum flexibility in torque control for a variety of step methods, from microstepping to full-step drive. Load current

is set in 1.56% increments of the maximum value.



Using Allegro's patented programming circuitry, the microstepping can be customised to match the motor for improved positional accuracy and reduced audible noise.



Synchronous rectification circuitry allows the load current to flow through the low 'on' resistance of the DMOS output driver during current decay. This feature eliminates the need for external clamp diodes in most applications, saving cost and external component count while minimising power dissipation.



Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout, overcurrent protection and crossover current protection. Special power-up sequencing is not required.



Targeted at the office automation and industrial markets, the A3992 is supplied in a low-profile (1.1 mm) 24L eTSSOP package (suffix LP) with exposed power tab and a 24-lead plastic dual-inline package with a copper batwing tab (suffix B). The power tab is at ground potential and needs no

electrical isolation.