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issue: February 2009 APPLIANCE Magazine

Motor Technology
Smart Integration

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A new smart motor controller provides an integrated solution for driving low-power, single-coil, brushless dc fans and motors.

A completely integrated motor control gives engineers less components to source and validate, providing an overall lower-cost solution.

The AH5792 smart motor controller from Diodes Inc. (Dallas, TX, U.S.; www.diodes.com) integrates a Hall sensor, amplifier, complete digital control circuitry, and a full bridge output driver into a low-profile, SOT553 package. Andy Davies, product marketing engineer, says these features reduce the amount of external components required to build a motor and, as a result, provide a lower-cost solution. “Most solutions today are not fully integrated,” Davies tells APPLIANCE. “Other vendors do not offer the Hall element.”

To achieve this level of integration, Davies says company engineers had to find the best process to support an “all-in-one” solution while keeping the die size small enough to allow it to be assembled into the SOT553 package. “We used a 0.6 µm CMOS platform with special functions,” he says. “This particular process allowed us to easily integrate the Hall sensor function from existing products without redesign and also yielded a chip size small enough to achieve the package design goal.”

The resulting package size is 1.5 × 1.1 mm – 5 pins. “Given that this is a single-chip solution, the size of the package was the best we could do to keep cost down and meet the die size and pin count,” Davies says.

To address reliability needs, the company also designed the controller with a wide temperature range of –40° to 100°C. “This feature allows a higher ambient temperature within an enclosure to be tolerated by the system electronics, which may impact decisions regarding venting [and] heat sinking of dissipative devices,” Davies explains. “Some products have to be sealed for environmental tolerance, and so any heat generated within the system must be tolerated to ensure reliability.”

The controller serves single-phase, full-wave, brushless dc (BLDC) motor control applications via its bidirectional (400 mA peak current rated) H-bridge output stage, and a pair of push-pull output drivers to source and sink current. According to Davies, the output stage can drain and sink at the same time using the classic ‘H’-bridge topology, but with no external components required. “This enables an easier design-in, PCB layout and lower system cost,” he says.

The device protects motor windings from damage with integrated, locked rotor detection. Automatic, self-restart functions shut down the output driver in the event of a locked rotor. “Automatic detection for rotor lock and a restart function prevents the motor coil from damage—burning up due to the winding being driven by the output stage—when the rotor is stuck, locked, or blocked,” Davies explains. “The rotor-lock detection circuitry senses when the rotor is stuck and disables the output drivers until it gets a signal that the rotor has been released, then it will re-enable the output drive function.”

Other features include an operating voltage range of 1.8 to 5 V, which aids miniature dc fans requiring low-voltage start-up, and a frequency generator output that provides users with tachometer-like feedback for external speed monitoring.

Ideal for low-voltage micromotors and ultrathin cooling fan applications, the controller can be used in consumer electronics, laptops, refrigeration, and automotive HVAC systems, according to Davies. “BLDC motor targets for possible appliance targets are for localized cooling of control electronics by small dc fans,” he says


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