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Integrated Circuits (ICs) Address Motor Similarities and Differences One of the advantages of low-power motors, beyond their modest current and voltage needs, is that MOSFET gate drivers can be integrated with controllers and optimized for the specic needs of different low-power DC motors. A look at a trio of related offerings from STMicroelectronics (ST) clearly illustrates this idea. This trio of ST products share many basic characteristics that simplify their use across multiple products with different motor types. They also provide ease modeling and require a minimal learning curve. Some of the features shared by these low-power, motor-drive ST products include: • High integration using microcontroller unit (MCU) interface, control logic, a driver, and a MOSFET power bridge (only a few non-critical, passive components—and no active, external components—are necessary) • A low operating voltage of 1.8V to 10V—which is well suited for low- voltage motors, especially those that are operated from small battery packs • A high output current of up to 1.3A (RMS) and 2A (peak) for each output bridge • A standby power consumption down to 80NA • Enhanced reliability due to under- voltage lockout (UVLO), as well as over-current and thermal protection • A small 3 × 3mm quad at no-lead (QFN) package An explanation of these three motor- drive ICs shows their similarities and differences. The STSPIN220, which is designed for stepper motors, integrates both control logic and a high-efciency, low drain-source on resistance R DS(ON) power stage (Figure 5). The controller implements a pulse-width • High-quality brushed motors can reach 10,000rpm, while BLDC motor designs can reach ve to even ten times that speed. • Brushed motors can operate directly from the power source and, thus, need just two wires, while BLDC motors need electronic commutation and at least three wires, plus any sensor wires. • Efciencies are roughly the same, but the sources of inefciency differ. For brushed motors, most inefciency comes from losses in the windings and brush-related friction, while BLDC motors experience the same— regarding winding losses—plus the additional eddy-current losses, which increase with speed. • Control circuitry is potentially more complex for steppers and simpler for brushed motors, but new ICs such as those from ST are largely eliminating these differences. • A low-end brushed motor, like those used for an inexpensive toy, can be the cheapest solution by far in terms of motors, wiring, and control electronics (if any), but obviously, it can provide only, very limited performance. References Countless motor-related references cover academic theory, implementations, applications, mechanical issues, electrical issues, thermal concerns, drive functions, and basic to advanced controls. One good reference is ST's An Introduction to Electric Motors. For more insight into stepper motors and microstepping (which is not as intuitive as brushed and brushless motors) look at ST's Application Note AN4923, STSPIN220: Step-Mode Selection and On-the-Fly Switching to Full-Step. modulation (PWM) current control with a programmable off time. It also allows a position resolution of 256 microsteps per full step, for extreme smoothness of motion. The similar siblings of the STSPIN220 include: the STSPIN230, a monolithic driver for the widely used three- phase BLDC motors; the STSPIN240 monolithic driver for two independent brushed DC motors; and the STSPIN250, which is for a single brushed DC motor. (Note: The STSPIN250 is for a single motor, compared to the two-motor STSPIN240. It can deliver a higher current of 2.6A (RMS) and 4A (peak).) All these ICs share front-end designs and operational commands to the extent possible; functionally, their differences lay in the motor-side interfaces. Making the Choice Confusing as it may seem, deciding which motor type to use is both an easy and difcult decision. Of course, whenever there are basic guidelines, there will be applications that are exceptions to these guidelines. Each motor type offers a different speed versus torque, angle versus torque, and stall behavior, which must be considered with respect to the application priorities and constraints. In general, situations that are a good t for the stepper motor are not suitable for either the brushed or brushless motor. The reason is that the former is better suited for constant start/stop/positioning priorities, while the latter two are better for continuous rotation. When choosing between a brushed or brushless motor, consider the following attributes: • Brushed motors have a more limited life than BLDC motors, with brushed motor life dependent on bearings and brush wear, while BLDC lifespan is a function of bearing wear only. Also, conductive dust from brush surface scraping can contaminate other surfaces. 17 MCU STBY Stepper Motor V REF V BAT R SENSE R SENSE GND OUTA 1 OUTA 2 OUTB 1 SENSE B SENSE A OUTB 2 T OFF EN/FAULT STCK/MODE 3 DIR/MODE 4 MODE 1 MODE 2 Logic Control Block Full Bridge Full Bridge Figure 5. The STSPIN220 integrates both control logic and a high-efciency, low on-resistance power stage for stepper motors. It includes a programmable off time for efciency and supports resolutions up to 256 microsteps per full step. (Source: STMicroelectronics)

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