May 1997
ML4411
*
/ML4411A
**
Sensorless Spindle Motor Controller
The ML4411A includes a comparator on the P3 output to
prevent cross-conduction.
FEATURES
s
Back-EMF commutation provides maximum torque
for minimum “spin-up” time for spindle motors
s
Accurate, jitter-free phase locked motor speed
feedback output
s
Linear or PWM motor current control
s
Easy microcontroller interface for optimized start-up
sequencing and speed control
s
Power fail detect circuit with delayed braking
s
Drives external N-channel FETs and P-channel FETs
s
Back-EMF comparator detects motor rotation after
power fail for fast re-lock after brownout
* This Product Is Obsolete
** This Product Is End Of Life As Of August 1, 2000
GENERAL DESCRIPTION
The ML4411 provides complete commutation for delta or
wye wound Brushless DC (BLDC) motors without the need
for signals from Hall Effect Sensors. This IC senses the
back EMF of the three motor windings (no neutral
required) to determine the proper commutation phase
angle using Phase Lock Loop techniques. This technique
will commutate virtually any 3-phase BLDC motor and is
insensitive to PWM noise and motor snubbing. The
ML4411 is architecturally similar to the ML4410 but with
improved braking and brown-out recovery circuitry.
Included in the ML4411 is the circuitry necessary for a
Hard Disk Drive microcontroller driven control loop.
The ML4411 controls motor current with either a constant
off-time PWM or linear current control driven by the
microcontroller. Braking and Power Fail are also included
in the ML4411.
The timing of the start-up sequencing is determined by the
micro, allowing the system to be optimized for a wide
range of motors and inertial loads.
The ML4411 modulates the gates of external N-Channel
power MOSFETs to regulate the motor current. The IC
drives P-Channel MOSFETs directly.
BLOCK DIAGRAM
BLDC
MOTOR
POWER
DRIVERS
GATE
DRIVE
LOGIC
AND
CONTROL
BACK-EMF
SAMPLER
VCO
LINEAR OR PWM
CURRENT CONTROL
POWER
FAIL
DETECT
RC
C
VCO
VCO/TACH OUT
RESET
ENABLE E/A
BRAKE
DIS PWR
I
CMD
I
LIMIT
PWR FAIL
+5
VCC
GND
C
OTA
C
OS
I
SENSE
C
BRK
3
N1-3
3
P1-3
VCC2
PH3
PH2
PH1
6
PATENTED
I
RAMP
20
14
15
16
21
18
26
8
28
27
17
19
25
22
23
24
4
7
12
13
6
1
1
2
ML4411/ML4411A
PIN CONFIGURATION
1
GND
Signal and Power Ground
2
P1
Drives the external P-channel
transistor driving motor PH1
3
P2
Drives the external P-channel
transistor driving motor PH2
4
V
CC2
12V power and power for the
braking function
5
P3
Drives the external P-channel
transistor driving motor PH3
6
C
OTA
Compensation capacitor for linear
motor current amplifier loop
7
C
BRK
Capacitor which stores energy to
charge N-channel MOSFETs for
braking with power off.
8
DIS PWR
A logic 0 on this pin turns off the N
and P outputs and causes the TACH
comparator output to appear on TACH
OUT
9-11 N1, N2 N3 Drives the external N-channel
MOSFETs for PH1, PH2, PH3
12 I
SENSE
Motor current sense input
13 C
OS
Timing capacitor for fixed off-time
PWM current control
14 C
VCO
Timing capacitor for VCO
15 VCO/TACH Logic Output from VCO or TACH
OUT
comparator
16 RESET
Input which holds VCO off and sets the
IC to the RESET condition
17 PWR FAIL
A “0” output indicates 5V or 12V is
under-voltage. This is an open
collector output with a 4.5ký pull-up
to +5V
18 ENABLE E/A A ”1” logic input enables the error
amplifier and closes the back-EMF
feedback loop
19 +5V
5V power supply input
20 RC
VCO loop filter components
21 I
RAMP
Current into this pin sets the initial
acceleration rate of the VCO during
start-up
22 PH1
Motor Terminal 1
23 PH2
Motor Terminal 2
24 PH3
Motor Terminal 3
25 V
CC
12V power supply. Terminal which is
sensed for power fail
26 BRAKE
A ”0” activates the braking circuit
27 I
LIMIT
Sets the threshold for the PWM
comparator
28 I
CMD
Current Command for Linear Current
amplifier
PIN NAME
FUNCTION
PIN NAME
FUNCTION
PIN DESCRIPTION
ML4411
28-Pin SOIC (S28W)
GND
P1
P2
VCC2
P3
C
OTA
C
BRK
DIS PWR
N1
N2
N3
I
SENSE
C
OS
C
VCO
I
CMD
I
LIMIT
BRAKE
VCC
PH3
PH2
PH1
I
RAMP
RC
+5V
ENABLE E/A
PWR FAIL
RESET
VCO/TACH OUT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
TOP VIEW
3
ML4411/ML4411A
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, T
A
= Operating Temperature Range, V
CC
= V
CC2
= 12V, R
SENSE
= 1ý, C
OTA
= C
VCO
= 0.01µF,
C
OS
= 0.02µF
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Oscillator (VCO) Section (V
PIN16
= 5V)
Frequency vs. V
PIN 20
1V - V
PIN20
- 10V
300
Hz/V
Frequency
V
VCO
= 6V
1450
1800
2150
Hz
V
VCO
= 0.5V
70
140
210
Hz
Reset Voltage at C
VCO
Mode = 0
125
250
mV
Sampling Amplifier (Note 1)
V
RC
State R
125
250
mV
I
RC
V
PIN18
= 0V, R
RAMP
= 39ký
70
100
130
µA
V
PIN18
= 5V, State A, V
PH2
= 4V
30
50
90
µA
V
PIN18
= 5V, State A, V
PH2
= 6V
–13
2
13
µA
V
PIN18
= 5V, State A, V
PH2
= 8V
–30
–50
–90
µA
V
PIN21
R
PIN21
= 39ký to +5V
1.0
1.1
1.20
V
Motor Current Control Section
I
SENSE
Gain
V
PIN27
= 5V, 0V - V
PIN28
- 2.5V
4.5
5
5.5
V/V
One Shot Off Time
12
25
33
µs
I
CMD
Transconductance Gain
0.19
mmho
I
CMD
, I
LIM
Bias Current
V
IN
= 0
0
–100
–400
nA
Power Fail Detection Circuit
12V Threshold
9.1
9.8
10.5
V
Hysteresis
150
mV
5V Threshold
3.8
4.25
4.5
V
Hysteresis
70
mV
Logic Inputs
Voltage High (V
IH
)
2
V
Voltage Low (V
IL
)
0.8
V
Current High (I
IH
)
V
IN
= 2.7V
–10
1
10
µA
Current Low (I
IL
)
V
IN
= 0.4V
–500
–350
–200
µA
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.
Supply Voltage (pins 4, 25) ........................................ 14V
Output Current (pins 2, 3, 5, 9,10,11) ................. ±150mA
Logic Inputs (pins 16, 17, 18, 25) .................... –0.3 to 7V
Junction Temperature ............................................ 150°C
Storage Temperature Range ..................... –65°C to 150°C
Lead Temperature (Soldering 10 sec.) .................... 150°C
Thermal Resistance (
q
JA
) ...................................... 60°C/W
OPERATING CONDITIONS
Temperature Range ........................................ 0°C to 70°C
VCC Voltage +12V (pin 25) ........................... 12V ± 10%
+5V (pin 19) ................................................ 5V ± 10%
I(RAMP) current (Pin 21) ................................. 0 to 100µA
I Control Voltage Range (pins 27, 28) ................ 0V to 7V
4
ML4411/ML4411A
ELECTRICAL CHARACTERISTICS
(Continued)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Braking Circuit (V
PIN17
= 0V)
Brake Active Threshold
0.8
1.2
1.6
V
PIN 26 Bias Current
V
PIN26
= 0V
0.3
1
µA
N-Channel Leakage
V
CC
, V
CC2
= 0V
0
0.06
10
nA
V
PIN17
= 0V, V
N
= 4V
C
BRK
Current
V
CC
, V
CC2
= 0V, V
PIN26
= 3V
20
85
µA
V
PIN7
= 6V
Outputs (I
CMD
= I
LIMIT
= 2.5V)
I
P
Low
V
P
= 0.8V
5
7
19.5
mA
V
P
= 0.4V
2
4
mA
V
P
High
I
P
= –10µA
V
CC
– 0.4
V
P3 Comparator Threshold
V
CC2
– 1.6
V
CC2
– 0.8
V
V
N
High
V
PIN12
= 0V
V
CC2
– 3.2
10
V
CC
– 1.2
V
V
N
Low
I
N
= 1mA
0.2
0.7
V
LOGIC Low (V
OL
)
I
OUT
= 0.4mA
0.5
V
VCO/TACH V
OH
I
OUT
= –100µA
2.4
V
POWER FAIL V
OH
I
OUT
= –10µA
V
PIN19
– 0.2 V
PIN19
– 0.1
V
PIN19
V
Supply Currents (N and P Outputs Open)
5V Current
3
4
mA
V
CC
Current
38
50
mA
V
CC2
Current
ML4411
2
3
mA
V
CC2
Current
ML4411A
2.6
3.75
mA
Note 1. For explanation of states, see Figure 5 and Table 1.
5
ML4411/ML4411A
maximum voltage at any PH input does not exceed VCC.
NEUTRAL
0
60
120
180
240
0
300
Figure 2. Typical motor phase waveform with Back-EMF
superimposed (Ideal Commutation)
VCO AND PHASE DETECTOR CALCULATIONS
The VCO should be set so that at the maximum frequency
of operation (the running speed of the motor) the VCO
control voltage will be no higher than VCC
MIN
– 1V. The
VCO maximum frequency will be:
F
POLES RPM
MAX
=
×
×
0 05
.
where POLES is the number of poles on the motor and
RPM is the maximum motor speed in Revolutions Per
FUNCTIONAL DESCRIPTION
The ML4411 provides closed-loop commutation for
3-phase brushless motors. To accomplish this task, a VCO,
integrating Back-EMF Sampling error amplifier and
sequencer form a phase-locked loop, locking the VCO to
the back-EMF of the motor. The IC also contains circuitry
to control motor current with either linear or constant off-
time PWM modes. Braking and power fail detection
functions are also provided on chip. The ML4411 is
designed to drive external power transistors (N-channel
sinking transistors and PNP sourcing transistors) directly.
Start-up sequencing and motor speed control are
accomplished by a microcontroller. Speed sensing is
accomplished by monitoring the output of the VCO,
which will be a signal which is phased-locked to the
commutation frequency of the motor.
BACK-EMF SENSING AND COMMUTATOR
The ML4411 contains a patented back-EMF sensing
circuit which samples the phase which is not energized
(Shaded area in figure 2) to determine whether to increase
or decrease the commutator (VCO) frequency. A late
commutation causes the error amplifier to charge the
filter (RC) on pin 20, increasing the VCO input while
early
commutation causes pin 20 discharge. Analog speed
control loops can use pin 20 as a speed feedback voltage.
The input impedance of the three PH inputs is about 8Ký
to GND. When operating with a higher voltage motor, the
PH inputs should be divided down in voltage so that the
FIGURE 1. BACK EMKF sensing block diagram
NEUTRAL
SIMULATOR
Φ
A +
Φ
B +
Φ
C
6
Φ
A
Φ
B
Φ
C
MULTIPLEXER
R
C1
C2
VCO
COMMUTATION
LOGIC
SIGN
CHANGER
b
a
–
+
I(PIN 21)
+
LOOP FILTER
I
RC
=
Va – Vb
8K
RC
VCO /TACH OUT
+
–
DIS PWR
8K
8K
ROTATION
SENSE
6
ML4411/ML4411A
Minute.
The minimum VCO gain derived from the specification
table (using the minimum Fvco at V
VCO
= 6V) is:
K
C
VCO MIN
VCO
(
)
.
=
×
−
2 42 10
6
Assuming that the V
VCO(MAX)
= 9.5V, then
C
F
VCO
MAX
=
×
×
−
9 5 2 42 10
6
.
.
or
C
POLES RPM
F
VCO
=
×
460
µ
0
2
4
6
8
10
12
3000
2500
2000
1500
1000
500
0
0.01
µ
F
0.02
µ
F
FREQUENCY (Hz)
V
VCO
(VOLTS)
Figure 3. VCO Output Frequency vs. V
VCO
(Pin 20)
Figure 4 shows the transfer function of the Phase Lock
Loop with the phase detector formed from the sampled
phase through the Gm amplifier with the loop filtered
formed by R, C1, and C2.
The impedance of the loop filter is
Z
s
C s
s
s
RC
LEAD
LAG
( )
(
)
(
)
=
+
+
1
1
ω
ω
R
C1
C2
VCO
–
+
Z
RC
RC
F
OUT
K
VCO
(HZ/V)
Gm = 1.25 x 10
–4
SAMPLED
PHASE
Figure 4. Back EMF Phase Lock Loop Components
Where the lead and lag frequencies are set by:
ω
LEAD
R C
=
1
2
ω
LAG
C
C
R C C
=
+
1
2
1 2
START-UP SEQUENCING
When the motor is initially at rest, it is generating no
back-EMF. Because a back-EMF signal is required for
closed loop commutation, the motor must be started
“open-loop” until a velocity sufficient to generate some
back-EMF is attained (around 100 RPM). The following
steps are a typical procedure for starting a motor which is
at rest.
Step 1: The IC is held in reset (state R) with full power
applied to the windings (see figure 6). This aligns the rotor
to a position which is 30° (electrical) before the center of
the first commutation state.
Step 2: Reset is released, and a fixed current is input to
pin 21 and appears as a current on pin 20, and will ramp
the VCO input voltage, accelerating the motor at a fixed
rate.
Step 3: When the motor speed reaches about 100 RPM,
the back EMF loop can be closed by pulling pin 18 high.
RESET/
ALIGN
P1, P3, N2 ON
OPEN-LOOP
(STEPPING)
CLOSED LOOP
VCO FREQUENCY
0
RESET
ENABLE E/A
Figure 6. Typical Start-up Sequence.
Using this technique, some reverse rotation is possible.
The maximum amount of reverse rotation is 360/N, where
N is the number of poles. For an 8 pole motor, 45° reverse
rotation is possible.
For quick recovery following a momentary power failure,
the following steps can be taken:
PIN
PIN
PIN
I
LIMIT
STEP
16
18
21
I
CMD
1
0
0
FIXED
I
MAX
2
1
0
FIXED
I
MAX
3
1
1
0
I
MAX
Table 2. Start-up Sequence.
7
ML4411/ML4411A
OUTPUTS
INPUT
STATE
N1
N2
N3
P1
P2
P3
SAMPLING
R OR 0
OFF
ON
OFF
ON
OFF
ON
N/A
A
OFF
OFF
ON
ON
OFF
OFF
PH2
B
OFF
OFF
ON
OFF
ON
OFF
PH1
C
ON
OFF
OFF
OFF
ON
OFF
PH3
D
ON
OFF
OFF
OFF
OFF
ON
PH2
E
OFF
ON
OFF
OFF
OFF
ON
PH1
F
OFF
ON
OFF
ON
OFF
OFF
PH3
Table 1. Commutation States.
R
RESET
0
A
B
C
D
E
F
A
4.3 V
C
VCO
2.3 V
VCO OUT
STATE
Figure 5. Commutation Timing and Sequencing.
ADJUSTING OPEN LOOP STEP RATE
I
RAMP
should be set so that the VCO’s frequency ramp
during “open loop stepping” phase of motor starting is less
than the motor’s acceleration rate. In other words, the
motor must be able to keep up with the VCO’s ramp rate
in open loop stepping mode. The VCO’s input voltage
(V
PIN 20
) ramp rate is given by:
dV
dt
I
C
C
VCO
RAMP
≈
+
1
2
since
F
K
V
VCO
VCO
VCO
=
×
K
C
VCO MAX
VCO
(
)
= ×
−
4 10
6
then combining the 3 equations I
RAMP
can be calculated
from the desired maximum open loop stepping rate the
motor can follow.
I
dF
dt
C
C
C
RAMP
VCO
VCO
<
×
+
×
−
(
)
1
2
6
4 10
Step 1a: The IC is held in reset (state R) with I
CMD
low
and DIS PWR low. The Micro Processor monitors the VCO/
TACH OUT pin to determine if a signal is present. If a
signal is present, the frequency is determined (by
measuring the period). If a signal is not present, proceed
to the routine described above for starting a motor which
is a rest.
Step 2a: Release RESET and DIS PWR. Apply a current to
pin 21 and monitor the VCO/TACH OUT pin for VCO
frequency.
Step 3a: When the VCO frequency approaches 6 X the
motor frequency (or where the motor frequency has
decelerated to by coasting during the time the VCO
frequency was ramping up) the back EMF loop can be
closed by pulling pin 18 high and motor current brought
up with I
CMD
or I
LIMIT
.
8
ML4411/ML4411A
The motor will start more consistently and tolerate a wider
variation in open loop step rate if there is some damping
on the motor (such as head drag) during the open loop
modes.
The tolerance of the open loop step VCO acceleration
dF
dt
VCO
depends on the tolerances of K
VCO
, I
RAMP
, C1,
C2, and C
VCO
. For more optimum spin up times, these
variables can be digitally “calibrated” out by the
microprocessor using the following procedure:
1. Reset the IC by holding pin 16 low for at least 5µs.
2. Go into open loop step mode with no current on
the motor and measure the difference between the
first two complete VCO periods with the PWM
signal at 50% duty cycle:
ENABLE E/A = (see below)
I
CMD
= 0V
PWM OUT = 50%
I(RAMP)
VCO/TACH OUT
PWM OUT
IN
MicroP
ML4411
Figure 7. Auto-Calibration of Open-Loop Step
Rate.
3. Compute a correction factor to adjust I