ML4426 Datasheet, PDF (1/16 Pages) Micro Linear Corporation – Bi-directional Sensorless BLDC Motor Controller

July 2000
ML4426*
Bi-directional Sensorless BLDC Motor Controller
GENERAL DESCRIPTION
FEATURES
The ML4426 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 ML4426 limits the motor current using a constant off-
time PWM control loop. The velocity loop is controlled
with an onboard amplifier. The ML4426 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.
s Motor starts and stops with power to IC
s Bi-directional motor drive for applications requiring forward/
reverse operation
s On-board start sequence: Align ® Ramp ® Set Speed
s Patented Back-EMF commutation technique provides jitterless
torque for minimum “spin-up” time
s Onboard speed control loop
s PLL used for commutation provides noise immunity from
PWM spikes, compared to noise sensitive zero crossing
technique
s PWM control for maximum efficiency
s Direct FET drive for 12V motors; drives high voltage motors
with IC buffers from IR, IXYS, Harris, Power Integrations,
Siliconix, etc.
(* Indicates Part Is End Of Life As Of July 1, 2000)
BLOCK DIAGRAM (Pin Configuration Shown for 28 Pin Version)
FB A
22
FB B
23
FB C
24
17
VDD ^CAT
750nA
–
1.5V
+
BACK
EMF
SAMPLER
19
VDD
CRT
750nA
–
1.5V
+
21
CRR
20
15
SPEED CVCO
FB
16
RVCO
VDD
500nA
VOLTAGE
CONTROLLED
OSCILLATOR
VCO/TACH
13
VCO
OUT
F/R
12
+
8
–
SPEED SET
3.9V
5
SPEED COMP
CT
6
1.7V
ISENSE
1
20kHz
1.7V
VCO
OUT
–
+
×5
–
VREF
+
16kΩ
R
A
F
B
E
C
D
ILIMIT
1-SHOT
8kΩ
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
1