How to Choose the Right Driver IC for Stepper Motors
How to Choose the Right Driver IC for Stepper Motors
This article discusses features and functionality offered by integrated circuits that simplify the task of controlling a stepper motor.
This article discusses features and functionality offered by integrated circuits that simplify the task of controlling a stepper motor.
In the previous article, we explored the issue of controlling a typical (i.e., brushed) DC motor using integrated circuits. These devices provide functionality that makes it much easier to implement a high-performance system built around a brushed DC motor, and the same is true for ICs that can drive stepper motors.
Quick Review: How to Control a Stepper Motor
A typical permanent magnet stepper motor has two windings. If the system uses a bipolar driver, rotation is achieved by applying a specific pattern of forward and reverse current through the two windings. Thus, bipolar drive requires an H bridge for each winding. Unipolar drive uses four separate drivers, and these do not need to be able to apply current in both directions: the center of the winding is provided as a separate motor connection, and each driver provides current flow from the center of the winding to the end of the winding. The current associated with each driver always flows in the same direction.
Generic ICs for Stepper Control
The first thing to keep in mind is that ICs intended for basic motor control functionality—or even just basic driver functionality—can be used with stepper motors. You don’t need an IC that is specifically labeled or marketed as a stepper-control device. If you’re using bipolar drive, you need two H bridges per stepper motor; if you’re taking the unipolar approach, you need four drivers for one motor, but each driver can be a single transistor, because all you’re doing is turning current on and off rather than changing its direction.
An example of a part in the “generic IC” category is the DRV8803 from Texas Instruments. This device is described as a “driver solution for any low side switch application.”
With a device like this, the center of the stepper motor’s windings is connected to the supply voltage, and the windings are energized by turning on the low-side transistors so that they allow current to flow from the supply, through half of the winding, through the transistor, to ground.
The generic-IC approach is convenient if you already own or have experience with a suitable driver—you can save a few dollars by reusing an old part, or you can save time (and reduce the likelihood of design mistakes) by incorporating a known and proven part into your stepper-controller schematic. The downside is that a more sophisticated IC could provide enhanced functionality and ensure a simpler design task, and this is why I prefer a stepper driver that has additional features.
Full-Featured Stepper Drivers
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Highly integrated stepper-motor controllers can greatly reduce the amount of design effort involved in higher-performance stepper-motor applications. The first beneficial feature that comes to mind is automated step-pattern generation—i.e., the ability to convert straightforward motor-control input signals into the required step patterns.
Let’s take the L6208, from STMicroelectronics, as an example.
Instead of logic inputs that directly control the current applied to the motor windings, the L6208 has
- a pin that selects between half steps and full steps,
- a pin that sets the direction of rotation,
- and a “clock” input pin that causes the internal motor-control state machine to advance by one step in response to a rising edge.
This interface is far more intuitive than the actual on/off sequences that are applied to the transistors connected to the windings (an example of which is given below).
