Allegro's
A4941 offers sensorless
commutation, a wide supply voltage range, 1.25 A peak output current, -40
to 105C operating temperature range, lock detection with auto restart, and a small
eTSSOP package with soft switching for reduced audible noise.
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 active. The BEMF sensing circuits and
adaptive commutation circuits determine when the state sequencer advances to
the next state.
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 crosses 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 automatically 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 is applied directly to the
motor 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 protection with auto restart. The
A4941GLP-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.
