Microstepping motor driver ICs feature built-in translator

Paul Boughton
Allegro Microsystems Europe is offering four new DMOS microstepping motor driver ICs featuring built-in overcurrent protection and targeted at the office automation market. The new A4982/A4984/A4985 and A4988 are complete microstepping motor drivers, each using a simple 'step and direction' interface and featuring a built-in translator for easy operation. The highly integrated devices require few external components and occupy a small footprint in a compact, thermally efficient package.
These devices are designed to operate bipolar stepper motors in full-, half-, quarter-, eighth- and sixteenth-step modes, with an output drive capacity of up to 35V and +/-2A. They include a fixed off-time current regulator that can operate in slow or mixed decay modes.
A built-in translator is said to be the key to the easy implementation of the devices. 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. According to Allegro Microsystems, the interface is an excellent fit for applications where a complex microprocessor is unavailable or already overburdened.
The chopping control circuitry automatically selects the current decay mode (slow or mixed). When a signal occurs at the 'step' input pin, the device determines if that step results in a higher or lower current in each of the motor phases. If the change is to a higher current, the decay mode is set to slow decay; if the change is to a lower current, the current decay is set to mixed decay. In this mode, the current is set initially to a fast decay for a period amounting to 31.25 per cent of the fixed 'off' time, then to a slow decay for the remainder of the 'off' time. This current decay control scheme is said to result in reduced audible motor noise, increased step accuracy and reduced power dissipation.
Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM (pulse width modulation) operation. Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout, crossover current, and over-current protection. Special power-on sequencing is not required.
For more information, visit www.allegromicro.com

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