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Design News, March 2013

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Automation & Control rotor around at the speed you desire. Simple enough, if you have done it before, and have time to tune the loop to your motor parameters to avoid miscommutation on every cycle. One way to simplify BLDC motor control is by using an out-of-the-box solution that combines a motor driver and microprocessor on a single evaluation module. This is still a motor driver plus MCU solution, but with a much simpler control algorithm called InstaSPIN-BLDC, which ships embedded in Flash on TI's low-cost MSP430G2553 MCU. Unlike traditional sensorless BLDC control techniques based on BEMF zero-crossing techniques as described above, InstaSPIN-BLDC monitors the motor's flux to determine when to commutate the motor. In field tests with more than 50 different motor types, InstaSPIN-BLDC gets the motor up and running in under 20 seconds. This robustness is due to the fact that InstaSPIN-BLDC doesn't require any knowledge about motor parameters.You only need to adjust one tuning value, which is the motor flux level. If lower currents are needed — less than 1.5 A — the options get even simpler and more integrated. Take, for example, sensorless motor drivers. If you have a battery, a PWM source like a 555 timer to control speed, and a motor, then you have all you need. The BEMF detection is integrated in the device and a simple state machine commutates the motor at the desired speed as determined by the PWM input. Locked rotor detection ensures successful restarts, should a disturbance occur in the system. DN Ryan Kehr is a manager of TI's motor applications team. For more information, go to www.ti.com. To read more, to go designnews.com. Table 1: Internal indexer logic. Design News | march 2013 | www.d esign n ews.com –54–

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