BLDC Motor Driver Delivers More Power

Feb 1, 2006 12:00 PM
By David Morrison, Editor, Power Electronics Technology

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The growing popularity of brushless dc (BLDC) motors is fueling demand for low-cost ICs capable of driving these three-phase motors. However, the IC-style drivers introduced to date have been limited to support of power levels below 200 W and voltages below 60 V. Apex Microtechnology's SA305 three-phase, BLDC pulse-width modulated (PWM) motor driver is a monolithic device capable of delivering 300 W with supplies up to 60 V, enabling the chip to drive BLDC motors in the one-third horesepower (hp) range. Typical applications include factory automation, robotic controls and positioning controls.

The SA305 employs three independent half-bridges to deliver up to 5 A of output current, or 10 A peak. This independent half-bridge operation provides separate high-side and low-side MOSFET control and allows the SA305 to be used wherever three high-current outputs are required. All six FETs in the device can be accessed independently to control the PWM and commutation (see the figure).

The motor driver, which is the company's first product targeted at the BLDC motor applications, also features unique control and protection features. It offers the designer a choice of digital interface — either DSP or MCU. This makes the driver suitable for applications requiring complex, multi-axis motion (DSP) or simpler motion-control applications (MCU). This part is also said to be the only 5-A brushless motor driver with three-phase current monitoring.

Prior to the SA305, BLDC motor drivers in the industrial voltage range needed to be implemented using discrete components. To assemble an equivalent discrete design typically requires six MOSFETs, three gate drivers, power resistors for current sensing and a handful of discrete components for thermal protection, according to Sam Robinson, senior applications engineer at Apex Microtechnology (Tucson, Ariz.). The board space required for the discrete approach is “easily a business card-sized design,” says Robinson.

In contrast, the SA305 is housed in a 23-pin staggered-lead IC package that measures 1.188 in. wide × 0.177 in. deep × 0.98 in. high. The latter dimension includes the lead length. Moreover, the SA305 switches at frequencies up to 100 kHz, so it can operate with relatively small filter components.

The SA305 also enables overall savings on system size, weight and design based on the device's PWM efficiency. In the application, efficiency would typically be around 90%. Because switching technology minimizes the driver's power dissipation, the need for large external heatsinks is reduced. It also means the motor and its operating system will run cooler, increasing long-term reliability.

Parts are now sampling with full-qualified release scheduled for the second quarter of 2006. In quantities of 10,000, pricing for the SA305 is $13.10. Additional information is available at www.apexmicrotech.com.

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