■ Supplementary Explanation (Cont.)
2. Occurrence of radio noises
When the lock protective function is being activated, coil
current supply/stop intervals are about 1 : 7 in terms of time
ratio.
When driving the motor with the AN8267S, radio noises
(noises which come out of the radio when the motor is driven
near it) may occur.
Assuming the external capacitor of the Pin4 to be of 1µF,
the supply/stop time ratio is about 0.3sec. : 2sec.
Lock Protective Function ON/OFF Time Calculation Expres-
sion
The radio noises are more likely to occur as the counter
electromotive power of the coil output pin rises more steeply.
So, they can be eliminated by attaching the external part men-
tioned in 1-2) above.
Reference Voltage 1 (V1)
Reference Voltage 2 (V2)
toff
ton
Steep Rise
Gentle Rise
Fig.6
Assuming the charging current to be Ich and the discharging
Fig.4
3. AN8267S lock protection
current to be IDC
At charge time ;
;
When the motor fan is locked, the AN8267S has a function
to protect the motor and IC. (lock protection operational prin-
ciple)
1
I ch · ton
C
V1 –V2 =
t on=
I ch dt =
∫
C
If the motor fan is locked, a sine wave signal is not input
from the Hall element any more and the potential of the Pin4
external capacitor increases. (Fig.5a)
(V1–V2)
I ch
· C
During this period, the IC is still supplying the coil current
to rotate the motor fan. Then, if the voltage at the Pin4 reach-
es the reference voltage 1 set inside the IC, the electric charge
in the external capacitor of the Pin4 is discharged constantly,
thus reducing the voltage at the Pin4. (Fig.5b)
At discharge time
1
V1–V2 =
C
I ch · toff
C
IDC dt =
∫
(V1–V2)
IDC
t off=
· C
The IC stops supplying the coil current when this constant
current discharge starts. If the voltage at the Pin4 reaches the
reference voltage 2, the IC starts charging a constant current
to the external capacitor of the Pin4 and supplies the coil cur-
rent again, thus repeating the above-mentioned operation.
Each value (typ.) of the AN8267S is ;
V1=4V
V2=0.95V
Ich=9.5µA
IDC=1.3µA
When C=1µF ;
ton=0.32s
C : External capacitor's capacity
toff=2.35s
Reference Voltage 1
4. Rotation output Pins2 and3
The Pins2 and 3 are of open collector output. The Pin2 is a
pulse output pin synchronized with a signal from the Hall ele-
ment. Therefore, the Pin2 is switched over depending on the
polarities of the Hall input Pins1 and 16.
Reference Voltage 2
a
b
Fig.5
1
L
H
16
H
L
2
H
L
The external capacitor of the Pin4 is always kept in the dis-
charge state by a signal from the Hall element at the time of
stationary rotation.
Polarities of Pins2, 1, and 16