FAN8420D3

11

Rev. 1.0.1

Oct. 2000.

Therefore, the output of the rotational direction detector is low, when the spindle rotates forward, and high in the reverse rota-

tion.

6. Reverse Rotation Prevention

• When the output of the OR Gate, A is LOW, it steers all the output current of the current sense Amp to the Gain Controller

zero. The output current of the Driver becomes zero and the motor stops.

• As in the state of the forward rotation, the D-F/F output, Q is HIGH and the motor rotates normally. At this state, if the

control input is changed such that EC>ECR, then the motor rotates slowly by the reverse commutation in the Driver. When

the motor rotates in reverse direction, the D-F/F output becomes Low and the OR Gate output, becomes LOW. This

prevents the motor from rotating in reverse direction. The operation principle is shown in the table and the flow chart.

Rotation

H2

H3

D-F/F(Q)

Reverse rotation preventer

Forward

H

H

→

→

→

→LH

Forward

-

Reverse

L

H

→

→

→

→L

L

-

Brake and stop

(b) Forward rotation

H1

H2

H3

+

−

+

−

+

−

Current

Sense

Amp

Gain

Controller

Driver

D-F/F

M

D

Q

CK

H3+

H3

−

H2+

H2

−

A

Low Active