ML4425 Datasheet, PDF (1/16 Pages) Fairchild Semiconductor – Sensorless BLDC Motor Controller

ML4425
Sensorless BLDC Motor Controller
www.fairchildsemi.com
Features
• Stand-alone operation
• Motor starts and stops with power to IC
• On-board start sequence: Align ♦ Ramp ♦ Set Speed
• Patented Back-EMF commutation technique provides
jitterless torque for minimum “spin-up” time
• Onboard speed control loop
• PLL used for commutation provides noise immunity from
PWM spikes, compared to noise sensitive zero crossing
technique
• PWM control for maximum efficiency
• Direct FET drive for 12V motors; drives high voltage
motors with IC buffers
Block Diagram
FB A
22
FB B
23
FB C
24
17
VDD ^CAT
750nA
–
1.5V
+
BACK
EMF
SAMPLER
19
VDD
CRT
750nA
–
1.5V
+
General Description
The ML4425 PWM motor controller provides all of the
functions necessary for starting and controlling the speed of
delta or wye wound Brushless DC (BLDC) motors without
Hall Effect sensors. Back EMF voltage is sensed from the
motor windings to determine the proper commutation phase
sequence using a PLL. This patented sensing technique will
commutate a wide range of 3-Phase BLDC motors and is
insensitive to PWM noise and motor snubbing circuitry.
The ML4425 limits the motor current using a constant off-
time PWM control loop. The velocity loop is controlled with
an onboard amplifier. The ML4425 has circuitry to ensure
that there is no shoot-through in directly driven external
power MOSFETs.
The timing of the start-up sequence is determined by the
selection of three timing capacitors. This allows optimization
for a wide range of motors and loads.
21
CRR
20
15
SPEED CVCO
FB
16
RVCO
VDD
500nA
VOLTAGE
CONTROLLED
OSCILLATOR
VCO/TACH
13
VCO
OUT
+
8
–
SPEED SET
3.9V
5
SPEED COMP
CT
6
1.7V
ISENSE
1
20kHz
1.7V
ILIMIT
12
VCO
OUT
–
+
×5
–
VREF
+
16kΩ
8kΩ
R
A
F
B
E
C
D
ILIMIT
1-SHOT
CIOS
26
COMMUTATION
STATE MACHINE
–
1.4V
+
VDD
4kΩ
UVLO
GATING
LOGIC
&
OUTPUT
DRIVERS
HA
2
HB
3
HC
4
LA
9
LB
10
LC
11
UV FAULT
18
REFERENCE
BRAKE
25
VDD
GND
RREF VREF
14
28
27
7
REV. 1.0.2 7/2/01