CAT

17

FB A

22

FB B

23

FB C

24

BACK

EMF

SAMPLER

CRT

19

–

+

–

+

1.5V

750nA

–

+

1.5V

750nA

VDD

VDD

CRR

21

500nA

VDD

SPEED

FB

20

CVCO

15

16

RVCO

VOLTAGE

CONTROLLED

OSCILLATOR

VCO/TACH

13

2

4

3

9

10

HA

HB

HC

LA

LB

GATING

LOGIC

&

OUTPUT

DRIVERS

+

–

SPEED SET

8

5

SPEED COMP

3.9V

1.7V

20kHz

6

CT

–

+

1.4V

1

ISENSE

× 5

UVLO

12

ILIMIT

–

+

1.7V

VREF

26

CIOS

16k

Ω

8k

Ω

ILIMIT

1-SHOT

25

BRAKE

VDD

4k

Ω

14

VDD

28

GND

27

RREF

11

LC

REFERENCE

VCO

OUT

VCO

OUT

18

UV FAULT

7

VREF

A

B

C

D

E

F

R

COMMUTATION

STATE MACHINE

July 2000

ML4425

Sensorless BLDC Motor Controller

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.

FEATURES

s

Stand-alone operation

s

Motor starts and stops with power to IC

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.

1