FAN8741 Datasheet, PDF (16/23 Pages) Fairchild Semiconductor – Spindle Motor and 6-CH Driver

5. Reverse Rotation Prevention(Spindle)
SPIN +
VREF -
HV+ +
HV-
-
HW+ +
HW- -
D
Q
CK
D-F/F
Low Active
A
Current
Sense
Amp
Gain
Controller
Driver
M
1) 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 VREF>SPIN, then the motor rotates slowly by the reverse commutation in the driver. When the
motor begins to rotate in the reverse direction, the D-F/F output becomes Low and the OR Gate output becomes Low. This
prevents the motor from continuing to rotate in the reverse direction. This operation principle is shown in the following table
and flow chart.
D-F/F
Reverse Rotation Preventer
Rotation
HV
HW
(Q)
V_REF<SPIN
V_REF>SPIN
Forward
H
H→L
H
Forward
-
Reverse
L
H→L
L
-
Brake and Stop
Forward rotation at VREF< SPIN
Rotating speed is decreased due to reverse torque at VREF>SPIN
and appropriate mute combination. (Motor still rotates forward)
At the moment that the motor rotates in reverse, the reverse rotation preventer makes
the output power stage equal to the short brake which is lower ,and three power transistors are fully turned on.
Motor rotates in reverse for short time due to motor inertia
Power stage remains in short brake scheme until forward rotation command is received.
16
FAN8741/FAN8742 Rev. 1.0.1
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