DMOS microstepping motor drivers with built-in overcurrent protection

The new 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 35 V and ±2 A. They include a fixed off-time current regulator which has the ability to operate in slow or mixed decay modes.

The built-in translator is 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. The interface is an ideal fit for applications where a complex microprocessor is unavailable or is 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. In this mode, the current is set initially to a fast decay for a period amounting to 31.25% of the fixed ‘off’ time, then to a slow decay for the remainder of the ‘off’ time).

This current decay control scheme results 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 operation. Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout, crossover current, and over-current protection. Special power-on sequencing is not required.



The A4982/A4984/A4985 and A4988 are offered in several different package options: 28- and 32-contact 5 mm x 5 mm x 0.90 mm QFN (ET) packages, a 24-contact 4.0 mm x 4.0 mm x 0.75 mm QFN (ES) package, and a 24-lead 7.8 mm x 4.4 mm x 1.2 mm eTSSOP (LP) package. All packages have exposed thermal pads for enhanced thermal dissipation, and are lead (PB) free with 100% matt tin-plated lead frames.