Micro Linear Corporation ML4435CP, ML4435CS, ML4435IP, ML4435IS Datasheet

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 commuta­tion control, Pulse Width Modulation (PWM) speed con­trol, 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 posi­tion 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 amplifi er
and PWM comparator that produces a PWM duty cycle
for speed regulation. Motor current is limited by a pulse­by-pulse PWM shutdown comparator that is tripped by
the voltage across an external current 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 Brush­less 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 effi ciency and minimum FET

sizing

n Onboard under voltage lock out and power fail detect

n Tach output senses commutation of the motor

* Some External Components Required.

May, 2000PRELIMINARY DATASHEET

PRELIMINARY

ML4435

WARRANTY

Micro Linear makes no representations or warranties with respect to the accuracy, utility, or completeness of the contents of
this publication and reserves the right to make changes to specifi cations and product descriptions at any time without notice.
No license, express or implied, by estoppel or otherwise, to any patents or other intellectual property rights is granted by this
document. The circuits contained in this document are offered as possible applications only. Particular uses or applications
may invalidate some of the specifi cations and/or product descriptions contained herein. The customer is urged to perform
its own engineering review before deciding on a particular application. Micro Linear assumes no liability whatsoever,
and disclaims any express or implied warranty, relating to sale and/or use of Micro Linear products including liability
or warranties relating to merchantability, fi tness for a particular purpose, or infringement of any intellectual property
right. Micro Linear products are not designed for use in medical, life saving, or life sustaining applications.

© Micro Linear 2000. 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; 5,777,514; 5,793,168; 5,798,635; 5,804,950; 5,808,455; 5,811,999; 5,818,207; 5,818,669; 5,825,165;
5,825,223; 5,838,723; 5.844,378; 5,844,941. Japan: 2,598,946; 2,619,299; 2,704,176; 2,821,714. Other patents are pending.

PRELIMINARY DATASHEET

May, 20002

BLOCK DIAGRAM

FB A

14

FB B

15

FB C

16

COMMUTATION

STATE MACHINE

R

3µs

SPEED SET

SPEED COMP

ISENSE

SOFT START

POWER ON

RESET PULSE

5

3

1

19

F

E

8.2 + 0.7V

2.2 + 0.7V

1V

225kΩ

225kΩ

NEUTRAL

5.8kΩ

2.9kΩ

TRIANGLE WAVE

SIMULATOR

A

B

C

D

LEVEL SHIFT

GENERATOR

CURRENT LIMIT

COMPARATOR

MUX

SPEED FB

–

+

COMP

–

PRELIMINARY

SIGN

CHANGER

6

+

0.7V

+
–

BACK

EMF SAMPLER

SPEED
ERROR AMP

+
–

PWM
COMPARATOR

+

–

5V

DQ

R

VREF + 0.7V

+

–

VOLTAGE

CONTROLLED

OSCILLATOR

GATING

LOGIC

AND

OUTPUT

DRIVERS

PULSE-BY-PULSE
CURRENT LIMIT

8.7V

+

–

+

LEVEL

0.97V

SHIFT

0.7V

COAST

UVLO COMPARATOR

COMP

–

1.5V

6V REFERENCE

+

COMP

–

0.9V

VREF

ML4435

18

SPEED FB

2

TACH

20

CVCO

RVCO

4

7

HA

8

HB

9

HC

11

LA

12

LB

13

LC

6

RT VCC GND

1710

ML4435 Block Diagram

May, 2000 PRELIMINARY DATASHEET 3

PIN CONFIGURATION

PRELIMINARY

ML4435

20-P n PDIP P20

20-P n SOIC S20

ISENSE

TACH

SPEED COMP

RVCO

SPEED SET

RT

HA

HB

HC

VCC

2

3

4

5

6

9

0

TOP VIEW

20

9

6

5

4

3

2

CVCO

SOFT START

SPEED FB

ND

FB C

FB B

FB A

LC

LB

LA

ML4435

PIN DESCRIPTIONS

PIN NAME FUNCTION

1 ISENSE Motor current sense input which triggers pulse by pulse current limit when
ISENSE exceeds 0.55V

2 TACH A clock output of 6 pulses per commutation cycle when SPEED FB is greater
than 0.97V otherwise the TACH output is at 5V

3 SPEED COMP Connection node for speed loop compensation components
4 RVCO Connection node for external resistor to set VCO frequency
5 SPEED SET DC input for setting motor speed
6 RT External resistor from this pin to ground controls the IC's PWM timing (frequency)
7 HA High-side output driver for motor phase A
8 HB High-side output driver for motor phase B
9 HC High-side output driver for motor phase C
10 VCC Power Supply input
11 LA Low-side output driver signal for motor phase A
12 LB Low-side output driver signal for motor phase B
13 LB Low-side output driver signal for motor phase C
14 FB A Back EMF signal input for motor phase A
15 FB B Back EMF signal input for motor phase B
16 FB C Back EMF signal input for motor phase C
17 GND Signal and power ground
18 SPEED FB Connection node for back-EMF sensing compensation components
19 SOFT START Connection node for external soft start capacitor which reduces start up current
20 CVCO Connection node for external capacitor to set VCO frequency. Forcing this input

below 1.5V causes the commutation to stop and the motor to coast

PRELIMINARY DATASHEET

May, 20004

PRELIMINARY

FUNCTIONAL DESCRIPTION

ML4435

COMPONENT SELECTION

Selecting external components for the ML4435 requires
calculations based on the motor’s electrical and mechani­cal parameters. The following is a list of the motor param­eters 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 other­wise specifi ed. 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 fi rst
approximation for selecting the closest standard value.

SUPPLY VOLTAGE AND ON-CHIP VOLTAGE
REFERENCE

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 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 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.

RSENSE

R

C

ISENSE

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.

May, 2000 PRELIMINARY DATASHEET 5

Figure 1. Current Limit with RSENSE

6

5

4

3

RSENSE Po er Rat n W

2

0

02

Figure 2. RSENSE Power vs. Motor Current

4

IMAX [MOTOR] A

60