Micro Linear ML4426IH Bi-directional sensorless bldc motor controller Datasheet

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 3Phase BLDC motors and is insensitive to PWM noise and
motor snubbing circuitry.
■ Motor starts and stops with power to IC
■ Bi-directional motor drive for applications requiring forward/
reverse operation
■ 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
The ML4426 limits the motor current using a constant offtime 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.
■ PLL used for commutation provides noise immunity from
PWM spikes, compared to noise sensitive zero crossing
technique
■ PWM control for maximum efficiency
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.
■ 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)
17
VDD
VDD
CAT
21
CRT
750nA
1.5V
FB C
24
15
16
SPEED CVCO
FB
RVCO
–
–
+
1.5V
+
VDD
FB B
23
20
CRR
750nA
FB A
22
19
500nA
BACK
EMF
SAMPLER
VCO/TACH
VOLTAGE
CONTROLLED
OSCILLATOR
13
VCO
OUT
VCO
OUT
F/R
R
A
12
F
B
+
–
8
E
3.9V
SPEED SET
COMMUTATION
STATE MACHINE
HA
C
HB
D
5
–
SPEED COMP
1.7V
6
CT
20kHz
1
ISENSE
–
×5
1.7V
GATING
LOGIC
&
OUTPUT
DRIVERS
+
–
VREF
+
+
1.4V
ILIMIT
1-SHOT
HC
LA
LB
LC
UVLO
VDD
16kΩ
UV FAULT
4kΩ
2
3
4
9
10
11
18
REFERENCE
8kΩ
26
CIOS
BRAKE
25
14
VDD
GND
28
27
RREF
7
VREF
1
ML4426
PIN CONFIGURATION
ML4426
28-Pin Narrow PDIP (P28N)
28-Pin SOIC (S28)
ISENSE
1
28
GND
HA
2
27
RREF
HB
3
26
CIOS
HC
4
25
BRAKE
SPEED COMP
5
24
FB C
CT
6
23
FB B
VREF
7
22
FB A
SPEED SET
8
21
CRR
LA
9
20
SPEED FB
LB 10
19
CRT
LC 11
18
UV FAULT
F/R 12
17
CAT
VCO/TACH 13
16
RVCO
VDD 14
15
CVCO
TOP VIEW
BRAKE
FB C
NC
2
23
FB B
SPEED COMP
3
22
FB A
CT
4
21
CRR
VREF
5
20
SPEED FB
SPEED SET
6
19
CRT
LA
7
18
UV FAULT
LB
8
RVCO
NC
CVCO
NC
VDD
17
10 11 12 13 14 15 16
VCO/TACH
9
LC
32 31 30 29 28 27 26 25
24
1
F/R
H3
TOP VIEW
2
CIOS
RREF
GND
NC
ISENSE
HA
HB
ML4425
32-Pin TQFP (H32-7)
CAT
ML4426
PIN DESCRIPTION
(Pin number in parenthesis is for TQFP package)
PIN
NAME
FUNCTION
PIN
1(30)
I SENSE
Motor current sense input. When
ISENSE exceeds 0.2 ´ ILIMIT, the
output drivers LA, LB, and LC are
shut off for a fixed time
determined by CIOS
17(17) CAT
A capacitor to GND sets the time
that the controller stays in the
align mode
18(18) UV FAULT
This output goes low when VDD
drops below the UVLO threshold,
and indicates that all output
drivers have been disabled
19(19) CRT
A capacitor to GND sets the time
that the controller stays in the
ramp mode
20(20) SPEED FB
Output of the back-EMF sampling
circuit and input to the VCO. An
RC network connected to SPEED
FB sets the compensation for the
PLL loop formed by the back-EMF
sampling circuit, the VCO, and
the commutation state machine
21(21) C RR
A capacitor to between CRR and
SPEED FB sets the ramp rate
(acceleration) of the motor when
the controller is in ramp mode
22(22) FB A
The motor feedback voltage from
phase A is monitored through a
resistor divider for back-EMF
sensing at this pin
23(23) FB B
The motor feedback voltage from
phase B is monitored through a
resistor divider for back-EMF
sensing at this pin
24(24) FB C
The motor feedback voltage from
phase C is monitored through a
resistor divider for back-EMF
sensing at this pin
25(25) BRAKE
A logic low input activates motor
braking by shutting off the highside output drivers and turning on
the low-side output drivers
26(26) CIOS
A capacitor to GND sets the time
that the low-side output drivers
remain off after ISENSE exceeds its
threshold
27(27) R REF
An 137kW resistor to GND sets a
current proportional to VREF that is
used to set all the internal bias
currents except for the VCO
28(28) GND
Signal and power ground
2(31)
HA
Active low output driver for the
phase A high-side switch
3(32)
HB
Active low output driver for the
phase B high-side switch
4(1)
HC
Active low output driver for the
phase C high-side switch
5(3)
SPEED COMP Speed control loop compensation is
set by a series resistor and capacitor
from SPEED COMP to GND
6(4)
CT
A capacitor from CT to GND sets
the PWM oscillator frequency
7(5)
V REF
6.9V reference voltage output
8(6)
SPEED SET
Speed loop input which ranges
from 0 (stopped) to VREF
(maximum speed)
9(7)
LA
Active high output driver for the
phase A low-side switch
10(8)
LB
Active high output driver for the
phase B low-side switch
11(9)
LC
Active high output driver for the
phase C low-side switch
12(10) F/R
This TTL level input selects the
direction of the motor by changing
the sequence of the commutation
state machine
13(11) VCO/TACH
This TTL level output corresponds
to the signal used to clock the
commutation state machine. The
output frequency is proportional to
the motor speed when the backEMF sensing loop is locked onto
the rotor position
14(12) V DD
12V power supply input
15(15) CVCO
A capacitor to GND sets the
voltage-to-frequency ratio of the
VCO
16(16) RVCO
An resistor to GND sets up a
current proportional to the input
voltage of the VCO
NAME
FUNCTION
3
ML4426
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.
V DD .......................................................................... 14V
Logic Inputs (BRAKE, F/R) ...................... GND - 0.3 to 7V
All Other Inputs and Outputs .. GND -0.3V to VDD + 0.3V
Output Current (LA, LB, LC, HA, HB, HC) ............ ±50mA
Junction Temperature .............................................. 150ºC
Storage Temperature Range ...................... –65ºC to 150ºC
Lead Temperature (Soldering 10 sec.) ..................... 260ºC
Thermal Resistance (qJA)
28-Pin Narrow PDIP ......................................... 48ºC/W
28-Pin SOIC ..................................................... 75ºC/W
32-Pin TQFP ..................................................... 80ºC/W
OPERATING CONDITIONS
Temperature Range
ML4426CX................................................. 0ºC to 70ºC
ML4426IX ............................................... –40ºC to 85ºC
V DD ......................................................... 10.8V to 13.2V
ELECTRICAL CHARACTERISTICS
Unless otherwise specified,VDD = 12V ± 10%, RSENSE = 1W, CVCO = 10nF, CIOS = 100pF, RREF = 137kW,
TA = Operating Temperature Range (Notes 1, 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
6.5
6.9
7.5
V
REFERENCE
VREF
Total Variation
Line, Temp
PWM OSCILLATOR
Total Variation
CT = 1nF
28
kHz
Ramp Peak
3.9
V
Ramp Valley
1.7
V
?
µA
Ramp Charging Current
SPEED CONTROL LOOP
SPEED SET Input Voltage Range
0
VREF
V
SPEED FB Input Voltage Range
0
VREF
V
SPEED COMP Output Current
±5
±20
µA
VSPEED SET = xV, VSPEED FB = yV
144
µ
W
SPEED SET Error Amp Transconductance
START-UP
CAT Charging Current
C Suffix
0.68
0.98
µA
I Suffix
0.5
1.1
µA
1.4
1.7
V
C Suffix
0.68
0.98
µA
I Suffix
0.5
1.1
µA
1.4
1.7
V
2.2
kHz
CAT Threshold Voltage
CRT Charging Current
CRT Threshold Voltage
VOLTAGE CONTROLLED OSCILLATOR
Frequency Range
RVCO = 5V, SPEED FB = 6V
1.5
Frequency vs. SPEED FB
RVCO = 5V, 0.5V £ SPEED FB £ 7V
1.85
300
Hz/V
CURRENT LIMIT
ISENSE Gain
One Shot OFF-Time
4
4.5
CIOS = 100pF
5.0
5.5
V/V
C Suffix
9
18
µs
I Suffix
9
20
µs
ML4426
ELECTRICAL CHARACTERISTICS
SYMBOL
(Continued)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LOGIC INPUTS (BRAKE, F/R) (Note 3)
V IH
Input High Voltage
2
V
VIL
Input Low Voltage
IIH
Input High Current
VIH = 2.4V
2.4
mA
IIL
Input Low Current
VIL = 0.4V
2.9
mA
0.8
V
LOGIC OUTPUTS (VCO/TACH, UV FAULT) (Note 3)
VCO/TACH Output High Voltage
IOUT = –100µA
VCO/TACH Output Low Voltage
IOUT = 400µA
UV FAULT Output High Voltage
IOUT = –10µA
UV FAULT Output Low Voltage
2.2
C Suffix
3.4
I Suffix
3.2
V
4.5
IOUT = 400µA
0.6
V
5.4
V
5.6
V
0.6
V
250
mV
BACK-EMF SAMPLER
SPEED FB Align Mode Voltage
125
SPEED FB Ramp Mode Current
SPEED FB Run Mode Current
C Suffix
500
720
nA
I Suffix
500
750
nA
C Suffix
30
90
µA
I Suffix
27
90
µA
State A, CRT = 5V, VPHB = VDD/2
–15
15
µA
State A, CRT = 5V,
C Suffix
–90
–30
µA
VPHB = 2´VDD/3
I Suffix
–90
–27
µA
0.5
1.2
mA
State A, CRT = 5V,
VPHB = VDD/3
OUTPUT DRIVERS
High Side Driver Output Low Current
VHX = 2V
High Side Driver Output High Voltage
IHX = –10µA
Low Side Driver Output Low Voltage
ILX = 1mA
Low Side Driver Output High Voltage
V(ISENSE) = 0V
VCC – 1.3
V
0.2
0.7
V
C Suffix VDD – 2.2
V
I Suffix VDD – 2.9
V
Phase C Cross-conduction Lockout Threshold
VDD – 3.0
V
SUPPLY
I DD
VDD Current
UVLO Threshold
UVLO Hysteresis
C Suffix
8.8
I Suffix
8.6
32
50
mA
9.5
10.2
V
10.3
V
150
mV
Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
Note 2: For explanation of states, see Figure 4 and Table 1.
Note 3: The BRAKE and UV FAULT pins each have an internal 4kW resistor to the internal reference.
5
ML4426
FUNCTIONAL DESCRIPTION
GENERAL
The ML4426 provides all the circuitry for sensorless speed
control of 3-phase Brushless DC (BLDC) motors. Controller
functions include start-up circuitry, back-EMF
commutation control, Pulse Width Modulation (PWM)
speed control, fixed OFF-time current limiting, braking,
and undervoltage protection.
The start-up circuitry aligns the motor to a known position,
then ramps up the motor speed to generate a back-EMF
signal. A back-EMF sampling circuit controls
commutation timing by forming a Phase Locked Loop
(PLL). The commutation control circuitry also outputs a
speed feedback (SPEED FB) signal used in the speed
control loop. The speed control loop consists of an error
amplifier and PWM comparator that produce a PWM duty
cycle for speed regulation. Motor current is limited by a
fixed OFF-time PWM shutdown comparator that is
controlled by an external sense resistor. Commutation
control, PWM speed control, and current limiting 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 BLDC motor
voltage and current requirements. Additional functions
include a braking function and undervoltage protection
circuit to shut down the output drivers in the event of a
low voltage condition on VDD of the ML4426.
COMPONENT SELECTION
If one or more of the above values is not known, it is still
possible to pick components for the ML4426, but some
experimentation may be necessary to determine the
optimal values. All quantities are in SI units unless
otherwise specified. The following formulas should be
considered as a starting point for optimization. All
calculations for capacitors and resistors should be used as
the first approximation for selecting the closest standard
value.
POWER SUPPLY AND REFERENCE
The supply voltage (VDD) is nominally 12V ±10%. A
100nF bypass capacitor to ground should be placed as
close as possible to VDD. A 6.9V voltage reference output
(VREF) is provided to set the speed command and current
limit of the ML4426. A 137kW from RREF to GND is
required to set up a reference current for internal
functions.
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 ML4426 translate to
outputs at these pins. LA, LB, and 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 and are 12V active low
signals.
Selecting external components for the ML4426 requires
calculations based on the motor’s electrical and
mechanical parameters. The following is a list of the
motor parameters needed for these calculations :
DC motor supply voltage – VMOTOR (V)
Maximum operating current – IMAX (A)
Number of magnetic poles – N
Back EMF constant – Ke (V-s/Rad)
VMOTOR
12V
Motor torque constant – Kt (Nm/A) (Kt = Ke in SI units)
Maximum speed of operation RPMMAX (RPM)
DC SUPPLY
CAPACITOR
Moment of inertia of the motor and load – J (Kg-m2)
Viscous damping factor of the motor and load – z
HA
HB
HC
MOTOR
PHASE A
LA
LB
MOTOR
PHASE B
MOTOR
PHASE C
LC
RSENSE
Figure 1. Using RSENSE in a 3-Phase 12V Power Stage
6
ML4426
FUNCTIONAL DESCRIPTION
(Continued)
CURRENT LIMITING IN THE POWER STAGE
FROM
RSENSE
PWM
ON/OFF
The current sense resistor (RSENSE) shown in Figure 1
regulates the maximum current in the power stage and
the BLDC motor. Current regulation is accomplished by
shutting off the output drivers LA, LB, and LC for a fixed
amount of time if the voltage across RSENSE exceeds the
current limit threshold.
ISENSE
×5
–
+
VREF
S
Q
R
Q
16kΩ
2.9V
R SENSE
8kΩ
0V
STOP
START
30µA
CIOS
The function of RSENSE is to provide a voltage
proportional to the motor current to set the current limit
trip point. The default trip voltage across RSENSE is
460mV, set by the internal ILIMIT divider ratio. The current
sense resistor should be a low inductance resistor such as
a carbon composition. For resistors in the milliohms range,
wire-wound resistors tend to have low values of
inductance. RSENSE should be sized to handle the power
dissipation (IMAX2 ´ RSENSE).
Figure 2. Current Sense Circuitry
ISENSE Filter
The ISENSE RC lowpass filter is placed in series with the
current sense signal as shown in Figure 2. The purpose of
this filter is to remove the diode reverse recovery
shootthrough current. This current causes a voltage spike
on the leading edge of the current sense signal which
may falsely trigger the current limit. The current sense
voltage waveform is shown before and after filtering in
Figure 3. The recommended starting values for this circuit
are R = 1kW and C = 330pF. This gives a time constant of
330ns, and will filter out spikes of shorter duration. C can
be increased to as much as 2.2nF, but should not exceed
a time constant of more than a few microseconds.
460mV
0V
(a)
(b)
Figure 3. Current Sense Resistor Waveforms
(a) Without Filtering, and (b) With Filtering
C IOS
When ISENSE exceeds 0.2 ´ ILIMIT, the current limit oneshot is activated, turning off LA, LB, and LC for a fixed
amount of time (tOFF). tOFF is set by the amount of
capacitance connected to CIOS. CIOS is usually set for a
fixed off time equal to or less than the PWM period. For a
25kHz PWM frequency, the PWM period is 40µs; tOFF
should be between 20µs and 40µs. The lower limit of tOFF
is dictated by the minimum on time of the power stage; a
safe approximation is 5µs or less. The equation for finding
the CIOS capacitance value is as follows:
COS =
t OFF ™ 50mA
2.4V
(1)
COMMUTATION CONTROL
A 3-phase BLDC motor requires electronic commutation
to achieve rotational motion. Electronic commutation
requires the switching on and off of the power switches of
a 3-phase half bridge. For torque production to be
achieved in one direction, the commutation is dictated by
the rotor position. Electronic commutation in the ML4426
is achieved by turning on and off, in the proper sequence,
one N output from one phase and one P output from
another phase. There are six combinations of N and P
outputs (six switching states) that constitute a full
commutation cycle. These combinations are illustrated in
Table 1 and Figure 4, and are labeled states A through F.
This sequence is programmed into the commutation state
machine. Clocking of the commutation state machine is
provided by a voltage controlled oscillator (VCO).
Forward/Reverse Control
The commutation sequence is reversed by pulling the F/R
pin to GND. This allows the motor to operate in the
opposite direction. This pin should change state only when
the motor is at rest. Either remove and restore power to
the ML4426, or pull the BRAKE pin and CAT pin to 0V to
stop the motor prior to changing the voltage on F/R. Either
method resets the internal commutation state machine,
and initiates a new start-up sequence.
7
ML4426
STATE
LA
LB
LC
OUTPUTS
HA
HB
HC
INPUT
SAMPLING
R
A
B
C
D
E
F
OFF
OFF
OFF
ON
ON
OFF
OFF
ON
OFF
OFF
OFF
OFF
ON
ON
OFF
ON
ON
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
OFF
OFF
OFF
ON
ON
OFF
N/A
FB B
FB A
FB C
FB B
FB A
FB C
Table 1. Commutation State Functions (Forward Direction)
A
B
C
D
E
F
A
B
C
D
E
F
HA
HIGH
SIDE
DRIVE
OUTPUTS
HB
HC
LA
LOW
SIDE
DRIVE
OUTPUTS
LB
LC
Figure 4. Output Commutation Sequence Timing Diagram (Forward Direction)
Cycle 1 - Full Commutation, Cycle 2 - Commutation with 50% PWM Duty Cycle
FUNCTIONAL DESCRIPTION
(Continued)
Voltage Controlled Oscillator (VCO)
The VCO provides a TTL compatible clock output on the
VCO/TACH pin proportional to the VCO input voltage at
the SPEED FB pin. The proportion of frequency to voltage
(VCO constant, Kv) is set by an 80.6kW resistor on RVCO
and a capacitor on CVCO as shown in Figure 5. RVCO sets
up a current proportional the VCO input voltage at SPEED
FB. This current is used to charge and discharge CVCO
between the threshold voltages of 2.3V and 4.3V. The
resulting triangle wave on CVCO corresponds to the clock
on VCO. Kv should be set so that the VCO output
8
frequency corresponds to the maximum commutation
frequency or maximum motor speed when the VCO input
is equal to or slightly less than VREF. CVCO is calculated
using the following equation:
C VCO =
6.5V ™ 3101
.
™ 10 -6
0.05
Hz œ Farad
V
Hz
™ N ™ SPEEDMAX
RPM
(2)
The closest standard value that is equal to or less than the
calculated CVCO should be used.
ML4426
FUNCTIONAL DESCRIPTION
(Continued)
The maximum frequency on the VCO pin is found by:
CVCO
fMAX = 0.05 ™ N ™ RPMMAX
RVCO
(3)
The voltage at the VCO/TACH pin is equal to the rotor
speed. The voltage at SPEED FB is controlled by the back
EMF sampler.
SPEED CVCO
FB
RVCO
BACK EMF SAMPLER
FROM
BACK EMF
SAMPLER
& RAMP
GENERATOR
The input to the voltage controlled oscillator is the back
EMF sampler. The back EMF sense pins FB A, FB B, and
FB C inputs to the back EMF sampler require a signal
from the motor phase leads that is below the VDD of the
ML4426. The phase sense input impedance is 8kW. This
requires a series resistor RES1 from the motor phase lead
as shown in Figure 6 based on the following equation:
1
RES1 = 670W / V ™ VMOTOR - 10V
6
5V
VCO/TACH
0V
Figure 5. External VCO Component Connections
The back EMF sampler measures the motor phase that is
not driven (i.e. if LA and HB are on, then phase A is
driven low, phase B is driven high, and phase C is
MOTOR ΦC
2.3V
(5)
This allows the ML4426 to compare the back EMF signal
to the motor's neutral point without the need for bringing
out an extra wire on a WYE wound motor. For DELTA
wound motors there is no physical neutral to bring out, so
this reference point must be calculated in any case.
MOTOR ΦB
CVCO
(4)
PH1+ PH2 + PH3
3
MOTOR ΦA
RESET
(FROM CAT)
VCO/TACH
4.3V
The back EMF sampler takes the motor phase voltages
divided down to signals that are less than VDD (12V
nominal) and calculates the neutral point of the motor by
the following equation:
Neutral =
VOLTAGE
CONTROLLED
OSCILLATOR
sampled). The sampled phase provides a back EMF signal
that is compared against the neutral of the motor. The
sampler is controlled by the commutation state machine.
The sampled back EMF is compared to the neutral through
an error amplifier. The output of the error amplifier outputs
a charging or discharging current to SPEED FB, which
provides the control voltage to the VCO.
RES1
FB A
RES2
FB B
NEUTRAL
SIMULATOR
RES3
FB C
ΦA + ΦB + ΦC
6
4kΩ
4kΩ
gm =
SIGN
CHANGER
4kΩ
+
–
1
8kΩ
TO
SPEED FB
MULTIPLEXER
4kΩ
4kΩ
4kΩ
COMMUTATION
STATE MACHINE
Figure 6. Back EMF Sampler Detailed Block Diagram
9
ML4426
FUNCTIONAL DESCRIPTION
(Continued)
BACK EMF SENSING PLL COMMUTATION CONTROL
CSPEEDFB1
Three blocks form a phase locked loop that locks the
commutation clock onto the back EMF signal: the
commutation state machine, the voltage controlled
oscillator, and the back EMF sampler. The complete phase
locked loop is illustrated in Figure 7. The phased locked
loop requires a lead lag filter that is set by external
components on SPEED FB. The components are selected
as follows:
K
N
= 0.25 ™
™
M d ln ™ f 100
f
d ™
= 2 ™ M ™ ln
100 N ™ K ™ 01- M5
=C
™ 0M - 15
O1
CSPEEDFB1
S
2
VCO
S
CSPEEDFB2
SPEEDFB1
CSPEEDFB2
20
SPEED
FB
FB A
VDD
22
FB B
23
FB C
24
500nA
BACK
EMF
SAMPLER
VOLTAGE
CONTROLLED
OSCILLATOR
VCO/TACH
13
2
VCO
R SPEEDFB
RSPEEDFB
O1
2
(6a)
F/R
R
12
A
(6b)
F
(6c)
E
B
PHASE
LOCKED
LOOP
C
D
COMMUTATION
STATE MACHINE
START-UP SEQUENCE
When power is first applied to the ML4426 and the motor
is at rest, the back EMF is equal to zero. The motor needs
to be rotating for the back EMF sampler to lock onto the
rotor position and commutate the motor. The ML4426 uses
an open loop start-up technique to bring the rotor from rest
up to a speed fast enough to allow back EMF sensing.
Start-up is comprised of three modes: align mode, ramp
mode, and run mode.
Align Mode (RESET)
Before the motor can be started, the rotor must be in a
known position. When power is first applied to the
ML4426, the controller is reset into the align mode. Align
mode turns on the output drivers LB, HA, and HC which
aligns the motor into a position 30 electrical degrees
before the center of the first commutation state. This is
shown as state R in the commutation states of Table 1.
Align mode must last long enough to allow the motor and
its load to settle into this position. The align mode time is
set by a capacitor connected to the CAT pin as shown in
Figure 8. CAT is charged by a constant 750µA current from
GND to 1.5 V until the align comparator trips to end the
align mode. A starting point for CAT is calculated as
follows:
C AT =
t S ™ 7.5 ™ 10 -7 ™ amp
15
. V
(7)
If the align time is not long enough to allow the rotor to
settle for reliable starting, then increase CAT until the
desired performance is achieved.
10
Figure 7. Back EMF Commutation Phase Locked Loop
Ramp Mode
At the end of align mode the controller goes into ramp
mode. Ramp mode starts commutating through the states
A through F as shown in Table 1. This ramps up the
commutation frequency, and therefore the motor speed,
for a fixed length of time. This allows the motor to reach a
sufficient speed for the back EMF sampler to lock
commutation onto the motor's back EMF. The amount of
time the ML4426 stays in ramp mode is determined by a
capacitor connected to the CRT pin as shown in Figure 8.
CRT is charged by a constant 750µA current from GND to
1.5 V until the ramp comparator trips to end the ramp
mode. This gives a fixed ramp time. CRT is calculated as
follows:
CRT =
2p ™ J ™ 5 ™ 10 -7 ™ amp ™ K V
IMAX ™ K t ™ 3 ™ N
(8)
The rate at which the ML4426 ramps up the motor speed
is determined by a fixed 500µA current source on the
SPEED FB pin. The current sources charges up the PLL
filter components causing the VCO frequency to ramp up.
During ramp mode, the back EMF sampler is disabled to
allow control of the ramping to be set only by the 500µA
current source. The ramp based on the SPEED FB filter is
generally too fast for the motor to keep up, so a capacitor
from CRR to SPEED FB can be added to slow down the
ramping rate. The optimal ramp rate is based on the motor
and load parameters and is can be adjusted by varying
the value of CRR.
ML4426
CRR
CAT
VDD
CRT
VDD
CAT
FB C
SPEED CVCO
FB
1.5V
RVCO
–
–
FB B
CRR
CRT
750nA
750nA
FB A
TO
SPEED FB
FILTER
+
1.5V
+
VDD
500nA
BACK
EMF
SAMPLER
VOLTAGE
CONTROLLED
OSCILLATOR
VCO/TACH
TO RESET INPUT
OF COMMUTATION
STATE MACHINE
Figure 8. ML4426 Start-up Circuitry for Controlling the Align and Ramp Times
Run Mode (Back EMF Sensing)
FROM
SPEED FB
At the end of ramp mode the controller goes into run
mode. In run mode, the back EMF sensing is enabled and
commutation is now under the control of the phase locked
loop. Motor speed is now regulated by the speed control
loop.
TO
GATING
LOGIC &
OUTPUT
DRIVERS
VREF
+
10kΩ
–
3.9V
SPEED SET
–
PWM SPEED CONTROL
RSC
Speed control is accomplished by setting a speed
command at SPEED SET with an input voltage from 0 to
6.9V (VREF). The accuracy of the speed command is
determined by the external components RVCO and CVCO.
There are a number of methods that can be used to control
the speed command of the ML4426. One is to use a 10kW
potentiometer from VREF to ground with the wiper
connected to SPEED SET. If SPEED SET is controlled from
a microcontroller, one of its DACs can be used with VREF
as its input reference.
The speed command is compared with the sensed speed
from SPEED FB through a transconductance error
amplifier. The output of the speed error amplifier is SPEED
COMP. SPEED COMP is clamped between one diode drop
above 3.9V (approximately 4.6V) and one diode drop
below 1.7V (approximately 1V) to prevent speed loop
“wind-up”. Speed loop compensation components are
connected to this pin as shown in Figure 9. The speed loop
compensation components are calculated as follows:
CSC =
R SC =
SPEED COMP
26.9 ™ N ™ VMOTOR ™ C VCO
2
. + 98.696 ™ tm ™ fSB
fSB ™ K e 25
2
10
2p ™ fSB ™ CSC
Where fSB is the speed loop bandwidth in Hz.
(9a)
(9b)
+
1.7V
CSC
CT
CT
20kHz
1.7V
PWM ON/OFF
FROM ILIMIT
ONE-SHOT
Figure 9. Speed Control Loop Component Connections
The voltage on SPEED COMP is compared with a ramp
oscillator to create a PWM duty cycle. The PWM ramp
oscillator creates a sawtooth function from 1.7V to 3.9V
as shown in Figure 9. A negative clamp at one diode drop
below 1.7V (approximately 1V) starts the oscillator on
power up. The frequency of the ramp oscillator is set by a
capacitor to ground CIOS and is selected using the
following equation:
1
CT =
™ 50mA
fPWM
2.4V
(10)
Where fPWM is the PWM frequency in Hz. The PWM duty
cycle from the speed control loop is gated the current
limit one shot that controls the LA, LB, and LC output
drivers.
11
ML4426
FUNCTIONAL DESCRIPTION
(Continued)
CROSS CONDUCTION COMPARATOR
When the ML4426 goes from align mode into ramp mode,
there is a possibility of cross conduction in phase 3 of the
bridge power stage. This cross conduction can happen
when HC is on in the align mode shown as state R in
Table 1, and the controller transitions to state A in ramp
mode where HC is turned off and LC is turned on. Cross
conduction can appear due to the differences in turn on
and turn off times of the power devices. To solve this
problem, the LC output driver is gated off until the HC is
equal to VDD – 3V as shown in Figure 10.
FROM
COMMUTATION
STATE MACHINE
UNDERVOLTAGE LOCKOUT
Undervoltage lockout is used to protect the 3-phase
bridge power stage from a low VDD condition.
Undervoltage is triggered at VDD of 9.5V or less and is
indicated by a TTL low output on the UV FAULT pin.
Undervoltage lockout also turns off all output drivers (LA,
LB, LC, HA, HB, and HC). The comparator that triggers
undervoltage lockout has 150mV of hystresis.
DESIGN CONSIDERATIONS
INTERFACING TO A 3-PHASE BRIDGE POWER STAGE
The ML4426 output drivers are configured to drive a 3
phase bridge power stage. For applications with buss
voltages from 12V up to 80V, level shifting circuitry can
be used to drive higher voltage P-channel MOSFETS for
the high side switches as shown in Figure 11.
The most flexible configuration is to use high side drivers
to control N-Channel MOSFETs (or IGBTs) which allows
applications from less than 12V up to 600V. Figure 12
shows the interface between the ML4426 and IR2118 high
side drivers from International Rectifier. This configuration
is capable of driving motors from busses of up to 320V.
The BRAKE pin can be pulsed prior to startup with an RC
circuit. This charges the bootstrap capacitors (C19, C20,
and C21) for the three high side drivers, allowing the reset
phase to operate normally. These capacitors must be sized
so that they stay sufficiently charged during the align
mode. Refer to AN-43 for additional applications
information on the ML4426.
12
HB
GATING
LOGIC
&
OUTPUT
DRIVERS
–
+
1.4V
9.5V
HC
LA
LB
+
LC
–
VDD
UV FAULT
4kΩ
BRAKING
When the BRAKE pin is pulled below 1.4V, the low side
output drivers LA, LB, and LC are turned on and the high
side output drivers HA, HB, HC are turned off. Braking
causes rapid deceleration of the motor and current
limiting is de-activated, and care should be taken when
using the BRAKE pin. BRAKE is has an internal 4kW pullup as shown in Figure 10, and can be driven by a switch
to ground, an open collector or drain logic signal, or a TTL
logic signal.
HA
FROM
SPEED CONTROL LOOP
& CURRENT LIMIT
2
3
4
9
10
11
18
REFERENCE
BRAKE
25
14
VDD
GND
28
27
RREF
7
VREF
Figure 10. Cross Conduction, Brake, and UVLO Circuits
ML4426
VBUSS
24V–80V
12V
C2
330µF
100V
C1
100nF
100V
R2
10kΩ
R3
10kΩ
R4
10kΩ
Q4
IRFR9120
Q5
IRFR9120
Q6
IRFR9120
Q1
2N6718
Q2
2N6718
Q3
2N6718
Q7
IRFR120
Q8
IRFR120
C3
1µF
Q9
IRFR120
MOTOR
R1
470mΩ
2W
R12
2kΩ
R14
2kΩ
R13
2kΩ
R15
1kΩ
C5
2.2nF
ML4425
R16
10kΩ
C9
100nF
C17
1nF
C12
ISENSE
GND
HA
RREF
HB
CIOS
HC
BRAKE
SPEED COMP
FB C
CT
FB B
VREF
FB A
R7
100Ω
R6
100Ω
S1
R8 (RES1)
R9 (RES1)
BRAKE
C14
CRR
LA
SPEED FB
LB
CRT
LC
UV FAULT
F/R
R5
100Ω
RUN
C16
330pF
R10 (RES1)
SPEED SET
R18
10kΩ
R21
787Ω
R20
137kΩ
C8
1µF
R17
10kΩ
C6
1µF
C7
100nF
CAT
VCO/TACH
RVCO
VDD
CVCO
C15
470nF
FORWARD
C4
R19
80.5kΩ
12V
REVERSE
C14
1µF
C13
100nF
Figure 11. Driving Lower Voltage Motors (12 to 80V)
13
ML4426
12V
IR2118
C16
100nF
25V
VCC
IN
VBUSS
24V–80V
C5
330µF
400V
D1
MUR150
VB
HO
COM
VS
NC
NC
R6
100Ω
IR2118
C17
100nF
25V
VCC
IN
C19
2.2µF
25V
R7
100Ω
Q1
IRF720
VB
HO
COM
VS
NC
NC
IR2118
C18
100nF
25V
VCC
IN
C20
2.2µF
25V
D3
MUR150
VB
HO
COM
VS
NC
NC
C21
2.2µF
25V
R8
100Ω
Q3
IRF720
Q2
IRF720
D2
MUR150
Q5
IRF720
Q4
IR720
Q6
IRF720
MOTOR
R12
470mΩ
2W
R1
1kΩ
C1
2.2nF
BOOTSTRAP
PRE-CHARGE
CAPACITOR
ML4425
R5
10kΩ
C4
1nF
C3
100nF
C15
100nF
R20
10kΩ
R9
100Ω
D6
(3×1N5819)
HA
RREF
HB
CIOS
HC
BRAKE
SPEED COMP
FB C
CT
FB B
VREF
FB A
R11
100Ω
R18
137kΩ
R14 (RES1)
SPEED FB
LB
CRT
LC
UV FAULT
R17
10kΩ
C12
1µF
C10
1µF
C11
100nF
CAT
VCO/TACH
RVCO
VDD
CVCO
C9
470nF
R16
80.6kΩ
12V
C7
100nF
Figure 12. ML4426 High Voltage Motor Drive Application Circuit
14
BRAKE
RAMP COMP
LA
C8
10nF
C6
1µF
S1
R15 (RES1)
C13*
FORWARD
REVERSE
RUN
C14
330pF
R13 (RES1)
F/R
R10
100Ω
D5
GND
SPEED SET
R19
787Ω
D4
ISENSE
ML4426
PHYSICAL DIMENSIONS
inches (millimeters
Package: H32-7
32-Pin (7 x 7 x 1mm) TQFP
0.354 BSC
(9.00 BSC)
0.276 BSC
(7.00 BSC)
0º - 8º
0.003 - 0.008
(0.09 - 0.20)
25
1
PIN 1 ID
0.276 BSC
(7.00 BSC)
0.354 BSC
(9.00 BSC)
0.018 - 0.030
(0.45 - 0.75)
17
9
0.032 BSC
(0.8 BSC)
SEATING PLANE
0.048 MAX
(1.20 MAX)
0.012 - 0.018
(0.29 - 0.45)
0.037 - 0.041
(0.95 - 1.05)
Package: P28N
28-Pin Narrow PDIP
1.355 - 1.365
(34.42 - 34.67)
28
0.280 - 0.296 0.299 - 0.325
(7.11 - 7.52) (7.60 - 8.26)
PIN 1 ID
1
0.045 - 0.055
(1.14 - 1.40)
0.100 BSC
(2.54 BSC)
0.020 MIN
(0.51 MIN)
0.180 MAX
(4.57 MAX)
0.125 - 0.135
(3.18 - 3.43)
0.015 - 0.021
(0.38 - 0.53)
SEATING PLANE
0º - 15º
0.008 - 0.012
(0.20 - 0.31)
15
ML4426
PHYSICAL DIMENSIONS
inches (millimeters)
Package: S28
28-Pin SOIC
0.699 - 0.713
(17.75 - 18.11)
28
0.291 - 0.301 0.398 - 0.412
(7.39 - 7.65) (10.11 - 10.47)
PIN 1 ID
1
0.024 - 0.034
(0.61 - 0.86)
(4 PLACES)
0.050 BSC
(1.27 BSC)
0.095 - 0.107
(2.41 - 2.72)
0º - 8º
0.012 - 0.020
(0.30 - 0.51)
0.090 - 0.094
(2.28 - 2.39)
SEATING PLANE
0.005 - 0.013
(0.13 - 0.33)
0.022 - 0.042
(0.56 - 1.07)
0.009 - 0.013
(0.22 - 0.33)
ORDERING INFORMATION
© Micro Linear 1998.
PART NUMBER
TEMPERATURE RANGE
PACKAGE
ML4426CP (End of Life)
ML4426CS (End of Life)
ML4426CH (End of Life)
0ºC to 70ºC
0ºC to 70ºC
0ºC to 70ºC
28-Pin PDIP (P28N)
28-Pin SOIC (S28)
32-Pin TQFP (H32-7)
ML4426IP (End of Life)
ML4426IS (End of Life)
ML4426IH (End of Life)
–40ºC to 85ºC
–40ºC to 85ºC
–40ºC to 85ºC
28-Pin PDIP (P28N)
28-Pin SOIC (S28)
32-Pin TQFP (H32-7)
is a registered trademark of Micro Linear Corporation. All other trademarks are the property of their respective owners.
Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483; 5,418,502;
5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; 5,652,479; 5,661,427; 5,663,874; 5,672,959; 5,689,167; 5,714,897;
5,717,798; 5,742,151; 5,747,977; 5,754,012; 5,757,174; 5,767,653;. Japan: 2,598,946; 2,619,299; 2,704,176. Other patents are pending.
Micro Linear reserves the right to make changes to any product herein to improve reliability, function or design. Micro Linear does not assume any liability
arising out of the application or use of any product described herein, neither does it convey any license under its patent right nor the rights of others. The circuits
contained in this data sheet are offered as possible applications only. Micro Linear makes no warranties or representations as to whether the illustrated circuits
infringe any intellectual property rights of others, and will accept no responsibility or liability for use of any application herein. The customer is urged to consult
with appropriate legal counsel before deciding on a particular application.
16
DS4426-01
2092 Concourse Drive
San Jose, CA 95131
Tel: 408/433-5200
Fax: 408/432-0295
www.microlinear.com
7/6/98 Printed in U.S.A.
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