AH280

Hall-Effect Smart Fan Driver

Anachip Corp.

www.anachip.com.tw

Rev. 0.7 Apr 16, 2004

4/7

Rotation detection

The automatic restart circuit detects a motor lock

condition and automatically turns off the output

current. When the lock condition is cleared, the IC

automatically restarts and allows the motor to run.

In the AH280, automatic restart is performed in the

following manner.

A motor lock condition is

detected when the Hall signal stops switching.

The output is ON when CT pin is being charged,

and OFF when CT pin is being discharged.

OFF

ON

CT

clamp

voltage

CT

comparator

voltage

T

off*

T

on*

CT

Motor locked

Motor locked detected

Motor output

Hall input

Motor locked

cleared

Reverts to normal operation

Determined by the CT pin capacitor

Where

CHG

I

)

CP

V

CL

(V

C

−

×

(sec)

DHG

I

)

CP

V

CL

(V

C

−

×

(sec)

C is the capacitance of the CT pin external capacitor