AH280
Hall-Effect Smart Fan Driver
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.
Hall input
ON
Motor output
OFF
CT
clamp
voltage
CT
comparator
voltage
Motor locked
Motor locked detected
T
on*
T
off*
CT
Motor locked
cleared
Reverts to normal operation
Output ON time (T
on
) and OFF time (T
off
)
Determined by the CT pin capacitor
Where
C
×
(VCL
−
V )
CP
(sec)
T
on
=
I
CHG
C
×
(VCL
−
VCP )
(sec)
T
off
=
I
DHG
C is the capacitance of the CT pin external capacitor
V
CL
is the CT pin clamp voltage
V
CP
is the CT pin comparator voltage
I
CHG
is the CT pin charge current
I
DHG
is the CT pin discharge current
Anachip Corp.
www.anachip.com.tw
4/7
Rev. 0.7 Apr 16, 2004
ANACHIP [ ANACHIP CORP ]
