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 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.
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
* Some External Components Required.
PRELIMINARY DATASHEET
May, 2000
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
