Stepper motors

The A3981 and A4980 from Allegro MicroSystems Europe are two new automotive-grade programmable stepper-motor driver ICs that are designed to operate bipolar stepper motors in full-, half-, quarter- and sixteenth-step modes at up to 28 V and ±750 mA in automotive, consumer and industrial applications.

Both devices offer a single-chip solution with internal digital timing circuitry and a built-in translator for ease of operation. The A3981 can be controlled by simple step and direction inputs, or through an SPI-compatible serial port that also can be used to program many of the integrated features and to read diagnostic information.

The A4980 is identical to the A3981 except for a low-voltage operation feature which will allow the IC to run down to a load supply voltage of 3.3 V (compared with 7 V on the A3981). This low voltage operation may be necessary in some automotive applications where the battery voltage during cold cranking can drop to a critically low level.

The built-in current regulator can be programmed to operate in fixed off-time or fixed-frequency PWM modes, with several decay modes available to reduce audible motor noise and increase step accuracy. In addition, the phase current tables can be programmed via the SPI interface to create unique microstepping current profiles to further improve motor performance for specific applications.

The current in each phase of the motor is controlled through a DMOS full bridge, using synchronous rectification to improve power dissipation. Internal circuits and timers prevent cross-conduction and shoot-through when switching between high-side and low-side drives. The outputs are protected from short circuits, and features for low load current and stalled rotor detection are included. Chip-level protection includes hot and cold thermal warnings, overtemperature shutdown, and overvoltage and undervoltage lockout.

The A3981 and A4980 are supplied in a 28-pin TSSOP power package with an exposed thermal pad (package type LP). This package is lead (Pb) free with 100% matt-tin lead-frame plating.