issue: August 2005 APPLIANCE Magazine Motor Technology Motor Driver Platform	Share  Printable format  Email this Article  Search
STMicroelectronics has introduced a family of monolithic smart motor drivers for medical appliances and other applications.

The new powerSPIN platform includes devices suitable for driving d.c. motors, stepper motors, and brushless d.c. motors, along with a comprehensive support package, including evaluation boards, PC software, and detailed application notes.

According to Thomas Hopkins, director of ST’s Power Systems Application Lab, the main advantage of the smart motor drivers is that the power stage is integrated into a single component, which reduces the system size while improving system reliability. “This series of devices includes over-current detection and thermal shutdown that provides protection against faults in the system that is not easily designed with discrete devices,” he tells APPLIANCE. “For the user, the design of the power stage is greatly simplified since the gate drive, bootstrap, and protection is built into the device.”

The powerSPIN devices are built with ST’s BCDIII process, which combines bipolar, CMOS, and isolated DMOS structures on the same chip to provide a robust 60-V mixed signal smart power technology. This is said to allow all of the control and power circuitry required to drive the motor to be integrated in a single chip. “The smaller geometry of the current generation of BCD improves the logic density, allowing more logic to be placed in the device and improving the power density of the power MOS with lower resistance-drain-to-source (RDSon) per unit area,” explains Mr. Hopkins. “This has allowed us to integrate two bridges and the control logic into one device, whereas in the previous generation, we were able only to integrate a single bridge with the same RDSon.”

As with most power integrated circuits, Mr. Hopkins says one challenge ST had to overcome was providing adequate heat sinking to the devices. “The PowerSO package used for these devices is a surface-mount package with a very good thermal impedance. Using a construction technique similar to discrete devices—where the die is attached directly to a heat slug that is also the back of the package—achieves a very low thermal impedance between the die and the case,” he explains. “When mounted on a standard multi-layer printed circuit board, an overall thermal impedance of around 15 Deg. C/W can be achieved. This low thermal impedance and the favorable RDSon of the output devices give the device the current driving capacity.”

With a wide 8- to 52-V operating voltage range, the powerSPIN platform can address a variety of motor control requirements in applications such as vending machines, medical devices, and office appliances. In a small fan or pump in a medical instrument, for example, using the integrated drivers would allow the designer to drive the motor with one IC connected directly to the outputs of a microcontroller, with no additional logic or interface needed. “This can represent a great savings in size and cost to the application,” Mr. Hopkins notes. “In some applications, it is possible to implement the motor control and mount the power devices directly on the back of the motor.”