Allegro'sA4941 offers sensorlesscommutation, a wide supply voltage range, 1.25 A peak output current, -40to 105C operating temperature range, lock detection with auto restart, and a smalleTSSOP package with soft switching for reduced audible noise.

Themotor drive system consists of three half bridge NMOS outputs, BEMF sensingcircuits, adaptive commutation control and state sequencer. The sequencerdetermines which output devices are active. The BEMF sensing circuits andadaptive commutation circuits determine when the state sequencer advances tothe next state.

Thethree half-bridge outputs are controlled by a state machine with six possiblestates. Motor BEMF is sensed at the tri-stated output for each state. BEMFsensing motor commutation relies on the accurate comparison of the voltage onthe tri-stated output to the voltage at the center tap of the motor. The BEMFzero crossing, the point where the tri-stated motor winding voltage crosses thecenter tap voltage, is used as a positional reference. The zero crossing occursroughly halfway through one commutation cycle.

Atstartup, commutations are provided by an onboard oscillator in order to stepthe motor to generate BEMF. When legitimate BEMF zero crossings are detectednormal BEMF sensing commutation is achieved.

Adaptivecommutation circuitry and programmable timers automatically determine theoptimal commutation points with minimal external components. Output speed canbe monitored with the FG output signal which occurs when a BEMF zero crossingis detected. Duty cycle control of the PWM input is applied directly to themotor windings to control speed or torque. The PWM input is also used todisable motor operation and put the IC into a low power sleep mode.

Protectionfeatures include thermal shutdown with hysteresis, under voltage lockout(UVLO), crossover current and locked rotor protection with auto restart. TheA4941GLP-T is supplied in a 16 lead TSSOP package with exposed power tab.The package is lead (Pb) free, with 100 percent matte tin lead frame plating.

Three-Phase Sensorless Fan Driver Designed for Fan and Blower Applications_A