July 2000

1, 2, or 3-Phase Variable Speed AC Motor Controller

BLOCK DIAGRAM

1

GENERAL DESCRIPTION

The ML4423 provides the PWM sinewave drive signals

necessary for controlling three phase AC induction motors as

well as single and two phase split capacitor AC induction

motors.

A constant voltage/frequency ratio can be maintained

over a frequency range of greater than 10:1, providing

15Hz to 150Hz control. The output variable frequency AC

voltages are sensed and fed back to the controller to track the

sinewave frequency and amplitude set at the speed control

input. Direction, on two and three phase motors, is controlled

by changing the relative phase difference between the motor

windings: 90

× for two phase motors and 120× and 240× for three

phase motors.

To protect the motor, power devices, high voltage drivers

and control circuitry, the ML4423 includes fixed period,

pulse by pulse variable duty cycle current limit, deadtime

circuitry, and undervoltage lockout. The ML4423 has

selectable output voltage swing of 5V or 12V for

interfacing to different high side drivers and power devices.

FEATURES

s

Drives single, two, and three phase AC motors

s

Greater than 10:1 variable speed control range

s

Constant V/F ratio with programmable end points

s

Reverse capability for two and three phase motors

s

Low distortion PWM sinewave drive

s

Eliminates run capacitors in PSC motors

s

Coast function for quick power disable

s

Low cost interface for various gate drivers

s

PWM current limit, undervoltage lockout, and

programmable deadtime

s

12V

±20% operation with onboard 8V reference

(* Indicates Part Is End Of Life As Of July 1, 2000)

VSPEED

5

CO

12

FB A

1

RSPEED

6

VMIN

4

VDD

GND

RREF

REFERENCE

VREF

26

CT

17

8

7

HA

HB

HC

LA

LB

GATING

LOGIC

&

OUTPUT

DRIVERS

PWM

SINE

WAVE

CONTROL

PWM

OSCILLATOR

SINE A

GENERATOR

SINE C

GENERATOR

SPEED

CONTROL

SINE B

GENERATOR

UVLO

LC

20

ISENSE

16

19

21

23

22

24

5V/12 SELECT

25

RDT

9

COAST

14

13

SINE A-C

27

SINE B-C

28

3PH/2PH

18

F/

R

15

+

–

COMP

0.5V

+

–

+

–

FB B

3

FB C

2

+

–

+

–