Complete control and drive for two-phase steppers

Two new families of translator/driver integrated circuits provide the complete control and drive functions for two-phase unipolar stepper motors.

Two new families of translator/driver integrated circuits provide the complete control and drive functions for two-phase unipolar stepper motors.

Combining low-power CMOS logic with high-current, high-voltage power FET outputs, the SLA7050M and SLA7060M Series of power multichip modules (PMCM) provide fixed-off-time, constant-current pulsewidth modulation (PWM) control of the output current.

Both devices offer full- or half-step control, and the SLA7060M Series also provides microstepping control.

These new devices are targeted at stepper-motor applications involving higher current, speed and torque levels, such as office automation, gaming machines, industrial machinery and vending equipment.

The wide motor operating voltage range (from 10 to 44V) means that these devices can operate with the majority of standard voltage systems, including 12, 24, 36 and 42V.

Versions are available with 1, 2 and 3A output current ratings, and the inputs are compatible with 3.3 or 5V logic.

The use of a built-in step translator to commutate the phases leads to simpler system designs with fewer components, and reduces the burden on external processors as well as the software complexity.

System design complexity is also reduced by the fact that no special power-up sequence is needed.

A "sleep" mode is also provided which reduces the bias current draw for more efficient operation.

The fixed off-time (12us typical) constant-current PWM drive leads to more consistent and controllable motor torque and higher step rates, while the ability to select synchronous or asynchronous PWM operation prevents the occasional beat frequency noise that can occur between the two energised phases during hold/detent states.

The devices incorporate 100V avalanche-rated N-channel MOS power switches with low on-resistance (300mohm typical), leading to improved reliability, lower temperature operation and lower power dissipation.

Mosfet body diodes with a typical rating of 0.8V at 1A are used as internal clamp diodes.

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