FAN8420D3

10

Rev. 1.0.1

Oct.. 2000.

4. Tsd (Thermal Shutdown)

When the chip temperature rises above 175

°C, the Q2 turns on and the output driver shuts down. When the chip temperature

falls off to about 150

°C, then the Q2 turns off and the driver operates normally. TSD has the temperature hysteresis of about

25

°C.

5. Rotational Direction Detection

• The forward and the reverse rotations of the CD are detected by the D-F/F and the truth table is shown in the above.

• The rotational direction of the CD can be explained by the output waveforms of the Hall sensors. The three outputs of Hall

sensors be H1, H2 and H3 respectively.

When the spindle rotates in reverse direction, the Hall sensor output waveforms are shown in Fig.(a). The phases order are

in H1

→H2→H3 with a 120°C phase difference.

On the other hand, if the spindle rotates in forward rotation, the phase relationship is H3

→H2→H1 as shown in fig.(b)

Gain

Controller

BIAS

Q2

20

+

−

+

−

DIR

D-F/F

D

Q

CK

H2+

H3+

H3

−

H2

−

Rotation

DIR

Forward

Low

Reverse

High

20

(a) Reverse rotation

H1

H2

H3