ML4435 Sensorless BLDC Motor Controller

The ML4435 provides all the circuitry for sensorless

speed control of 3 phase Brushless DC Motors. Controller

functions include start-up circuitry, Back EMF commuta-

tion control, Pulse Width Modulation (PWM) speed con-

trol, 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 posi-

tion 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 pulse-

by-pulse PWM shutdown comparator that is tripped by

the voltage across an external current sense resistor. Com-

mutation control, PWM speed control, and current limit-

ing 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 Brush-

less 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 ML4435.

May, 2000

PRELIMINARY DATASHEET

GENERAL DESCRIPTION

FEATURES

n Proprietary back-EMF sensing commutation technique

for motor communication without hall effect sensors

n PWM pulse-by-pulse current limiting to protect motor

and FET drivers

n Stand-alone operation; motor starts and stops with

power applied to the IC*

n Soft-start function limits start-up current

n PWM speed control for efficiency and minimum FET

sizing

n Onboard under voltage lock out and power fail detect

n Tach output senses commutation of the motor

PRELIMINARY

* Some External Components Required.