ML4435

PRELIMINARY ML4435 Sensorless BLDC Motor Controller GENERAL DESCRIPTION The ML4435 provides all the circuitry for sensorless speed control of 3 phase Brushless DC Motors. Controller functions include start-up circuitry, Back EMF commutation control, Pulse Width Modulation (PWM) speed control, pulse-by-pulse current limiting, motor coasting, and under-voltage protection. Motor starting is accomplished by commutating the motor at a low frequency to produce low speed motion. The low speed motion is used to generate a Back EMF signal. A back EMF sampling circuit locks on to the motors position and controls commutation timing by forming a phase locked loop (PLL). The commutation control circuitry also outputs a speed feedback signal used in the speed control loop. The speed control loop consists of an error amplifier and PWM comparator that produces a PWM duty cycle for speed regulation. Motor current is limited by a pulseby-pulse PWM shutdown comparator that is tripped by the voltage across an external current sense resistor. Commutation control, PWM speed control, and current limiting are combined to produce the output driver signals. Six output drivers are used to provide gating signals to an external 3 phase bridge power stage sized for the Brushless DC (BLDC) motor voltage and current requirements. Additional functions include a motor coast function and an under voltage lock out circuit to shut down the output drivers in the event of a low voltage condition on the VCC to the M...