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PDF ML4435 Data sheet ( Hoja de datos )
| Número de pieza | ML4435 | |
| Descripción | Sensorless BLDC Motor Controller | |
| Fabricantes | Micro Linear | |
| Logotipo |  |
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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
PRELIMINARY DATASHEET
* Some External Components Required.
May, 2000
1 page  
PRELIMINARY
ML4435
FUNCTIONAL DESCRIPTION
COMPONENT SELECTION
Selecting external components for the ML4435 requires
calculations based on the motor’s electrical and mechani-
cal parameters. The following is a list of the motor param-
eters needed to for these calculations:
The maximum DC motor supply voltage V MOTOR (V)
The maximum operating current I MAX (A)
The winding resistance measured line to line Rl-l Ω
The number of magnetic poles N (Unitless)
The Back EMF constant Ke (V s/RAD)
The torque constant Kτ (N m/A) of the motor (Kτ = Ke
in SI units)
The maximum speed of operation RPMMAX (RPM)
The moment of inertia J (Kg m2 ) of the motor and its
load
The viscous damping factor ζ (Unitless) of the motor and
its load
If one or more of the above values is not known, it is
still possible to pick components for the ML4435, but
some experimentation may be necessary to determine the
optimal values. All quantities are in SI units unless other-
wise specified. The following formulas and component
selection graphs should be considered as a starting point
from which to optimize the application. All calculations
for capacitors and resistors should be used as the first
approximation for selecting the closest standard value.
SUPPLY VOLTAGE AND ON-CHIP VOLTAGE
REFERENCE
VCC
The supply voltage at VCC (pin 10) is nominally
12V ± 10%. A bypass capacitor of 0.1µF to ground as
close as possible to VCC (pin 10) is recommended.
RT
An internal 6V reference is generated inside the ML4435.
The reference appears on RT (pin 6). A resistor to ground
on RT sets the PWM frequency. This resistor can be
replace with a potentiomenter for use in setting the speed
command. This topic is discussed under the PWM SPEED
CONTROL section. Note: Buffer this pin with an op amp
with at least a 1MΩ input impedance if external circuits
are necessary.
OUTPUT DRIVERS
The output drivers LA, LB, LC, HA, HB, and HC provide
totem pole output drive signals for a 3 phase bridge power
stage. All control functions in the ML4435 translate to
outputs at these pins. LA, LB, LC provide the low side drive
signals for phases A, B, and C of the 3 phase power stage
and are 12V active high signals. HA, HB, and HC provide
the high side signals for phases A, B, and C of the 3 phase
power stage and are 12V active low signals.
CURRENT LIMITING IN THE 3 PHASE BRIDGE
POWER STAGE
A current sense resistor RSENSE shown in Figure 1 is
installed in the 3 phase power stage to regulate the maxi-
mum current in the power stage and the BLDC motor.
Current regulation is accomplished by shutting off the
output drivers LA, LB, and LC for the remainder of the
PWM period if the voltage across RSENSE exceeds the
current limit threshold set by the SOFT START (pin 19).
The maximum power dissipated in RSENSE is shown in
Figure 2.
R
RSENSE
C
ISENSE
Figure 1. Current Limit with RSENSE
6
5
4
3
2
0
024
6
IMAX [MOTOR] A
0
Figure 2. RSENSE Power vs. Motor Current
May, 2000 PRELIMINARY DATASHEET
5
5 Page 
PRELIMINARY
FUNCTIONAL DESCRIPTION
ML4435
Figure 14b. Power Stage
May, 2000 PRELIMINARY DATASHEET
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet ML4435.PDF ] | |
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