The Ton values, given by KCx1Rx1, must be less than the period of the Hall effect electrical signal at

the desired motor speed , so Ton must meet the requirement of 1.1 :

( 1.1 ) Ton

<

60

n

⋅ ωm

For the motor and the load used in this application, which have the following parameters :

Jt = 10

Kt = 10

B = 10

n=4 ;

R1=100k +/- 10% [k

Ω]

;

R2=1M

±1[kW]

;

Cf=220n [F]

A regulated speed of 6000RPM can be obtained with an accuracy of around +/-3%, considering Ton ac-

curacy of +/-1% , the V5 and Vref mismatch of +/-1% .

If the speed is 6000RPM, there are 100 rotor revolution for second, with n=4, the Hall effect frequency

is 400Hz. Therefore Ton has to be lower than 2.5ms (according to equation 1.1).

The phase margin is about 45° and the response time of the speed loop for a speed step variation is

around 200ms .

6X6 BRUSHLESS APPLICATION

Vcontrol

Constant Toff PWM

Current Control. Two M74HC124 plus an LM339

THREE PHASE

BRUSHLESS

MOTOR

IN1B

IN1A

IN2A

EN2

EN1

OUT3

L6234

EN3

EN1

EN2

IN3

IN2

IN1

OUT2

OUT1

Vboot

Vcp

Vs

Vs

100uF

1N4148

1N4148

10nF

220nF

100nF

GND

Vref

SENSE1

1uF

SENSE2

IN3B

IN3A

IN2B

EN3

OUT3

L6234

EN3

EN1

EN2

IN3

IN2

IN1

OUT2

OUT1

Vboot

Vcp

Vs

Vs

100uF

1N4148

1N4148

10nF

220nF

100nF

GND

Vref

SENSE1

1uF

SENSE2

M74HC123

monostable

+5V

100nF

23

16

4

15

14 8

1

+5V

+5V 100nF

LM339

470pF

1K

1

+5V

8

+

-

_

Q

A

B

4

Comparator & monostable

Comparator & monostable

Comparator & monostable

CONTROL

LOGIC

Vsense1

Vsense2

Vsense3

PWM1

PWM2

PWM3

OUT1A

OUT1B

OUT2A

OUT2B

OUT3B

OUT3A

SPEED AND POSITION

FEEDBACK

Figure 24. 6x6 Three Phase Brushlees Application Circuit

AN1088 APPLICATION NOTE

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