The A4934 is a three phase, sensorless, brushless DC motor driver. Propriety BEMF sensing eliminates the requirement of Hall sensor ICs for commutation. Operating voltage range is 8 to 16V with a peak output current rating of 1.25A.
The motor drive system consists of three half bridge NMOS outputs, BEMF sensing circuits, adaptive commutation control, and state sequencer. The sequencer determines which output devices are ac¬tive. The BEMF sensing circuits and adaptive commutation circuits determine when the state sequencer advances to the next state.

A complete self contained BEMF sensing commutation scheme is provided. The three half-bridge outputs are controlled by a state machine with six possible states. Motor BEMF is sensed at the tri-stated output for each state.

BEMF sensing motor commutation relies on the accurate comparison of the voltage on the tri-stated output to the voltage at the center tap of the motor. The BEMF zero crossing, the point where the tri-stated motor winding voltage cross¬es the center tap voltage, is used as a positional reference. The zero crossing occurs roughly halfway through one commutation cycle.
At startup, commutations are provided by an onboard oscillator in order to step the motor to generate BEMF. When legitimate BEMF zero crossings are detected normal BEMF sensing commutation is achieved. Adaptive commutation circuitry and programmable timers auto¬matically determine the optimal commutation points with minimal external components. Output speed can be monitored with the FG output signal which occurs when a BEMF zero crossing is detected. Duty cycle control of the PWM input are applied directly to the mo¬tor windings to control speed or torque. The PWM input is also used to disable motor operation and put the IC into a low power sleep mode. Protection features include thermal shutdown with hysteresis, under voltage lockout (UVLO), crossover current and locked rotor protec¬tion with auto restart.

The A4934GLP-T is supplied in a 16 lead TSSOP package with ex¬posed power tab. The package is lead (Pb) free, with 100%matte tin leadframe plating.