Stepper-motor driver has easy MPU interface
An Allegro Microsystems product story
Edited by the Electronicstalk editorial team Jun 10, 2005
A new bipolar stepper-motor driver has built-in translator circuitry that makes it very easy to interface to microprocessor-based control systems in office automation and industrial applications.
The new A3982 from Allegro MicroSystems Europe is a bipolar stepper-motor driver integrated circuit featuring built-in translator circuitry that makes it very easy to interface to microprocessor-based control systems in office automation and industrial applications.
The A3982 has DMOS outputs rated at 35V and +/-1.5A (2 A peak).
Low on-resistance DMOS outputs, along with synchronous rectification, result in low-power dissipation, allowing higher motor currents and leading to reduced temperature rise.
The device is controlled via a simple two-wire step and direction interface for easy operation in full- or half-step modes, and is housed in a 24-pin SOIC package (15.4 x 7.5mm) that is 20-50% percent smaller than competing ICs in the same current range.
The translator is key to the easy implementation of the A3982.
Simply inputting one pulse on the step input causes the motor to take one step.
There are no phase sequence tables, high-frequency control lines or complex interfaces to program.
As a result, the A3982 is ideal for applications with multiple motors that would normally push the I/O capacity of most microprocessor controllers.
Internal synchronous rectification control circuitry is included in the A3982 to improve power dissipation during PWM operation.
The power dissipation savings (typically greater than 20%) result in lower temperature rise and eliminate the need for external Schottky diodes.
Competitive devices with bipolar outputs cannot implement synchronous rectification.
The A3982 operates in full- and half-step modes.
In half-step mode, the current in each phase is switched between 100% current (one phase on), 70.7% (two phases on) and 0%.
This sequencing of the current results in the same torque being produced in each step and therefore more predicable operation.
The A3982 includes a fixed off-time output current regulator, which automatically selects slow- or mixed-decay modes.
When a step signal occurs, the A3982 determines if the 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, then the decay mode is set to mixed decay with 31.25% fast and 68.75% slow decay.
This patented current decay scheme results in reduced audible noise, increased step accuracy and reduced power dissipation.
Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout and crossover current protection.
Special power-up sequencing is not required.
The A3982 is manufactured using the Allegro ABCD (Allegro bipolar CMOS DMOS) process.
The 24-pin SOIC package options include a lead-free (Pb-free) version.
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