The Melexis MLX90283 vibration motor driver IC from Melexis Microelectronic Integrated Systems (Concord, NH) is designed to overcome the problem of single-phase brushless dc motors starting in the incorrect position, which could lead to unreliable start-up or a locked rotor condition and prevent functioning of a vibrating alert in a mobile phone or PDA.
The IC detects a locked state within 110 ms by sensing the rotor magnetic field. Once this detection period has elapsed, the device enters in Active Start and applies a 55 Hz frequency to the motor coil. The Active Start circuitry shakes the rotor in an optimal forward and reverse ratio to ensure reliable start-up in the forward direction.
The MLX90283 integrates a Hall-effect sensor and digital and power driver circuitry. Operating voltage is 1.8 to 3.6 V. The IC uses a “Freewheel” principle, whereby the device switches off its outputs when the torque approaches zero and delays the next switchover using a delay of typically 92 microseconds. As the device activates the Freewheel when the torque is close to zero, the rotational speed is unchanged. This design cuts average motor current consumption by 10% while keeping the same rotation speed, thus helping to achieve high efficiency.
Housed in a quad flat pack, no lead package, the IC measures 1.5 × 2 mm and is 0.43 mm thick, suiting it for vibration motors in slim mobile phone and consumer electronics devices. List price is $0.32 each in quantities of 5,000, with samples available on request.
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