AN8267S Datasheet, PDF (4/5 Pages) Panasonic Semiconductor – Fan Motor Driver

s Supplementary Explanation (Cont.)
2. Occurrence of radio noises
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.
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.
When the lock protective function is being activated, coil
current supply/stop intervals are about 1 : 7 in terms of time
ratio.
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
Reference Voltage 1 (V1)
Steep Rise
Gentle Rise
Fig.4
3. AN8267S lock protection
When the motor fan is locked, the AN8267S has a function
to protect the motor and IC. (lock protection operational prin-
ciple)
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)
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)
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.
Reference Voltage 1
Reference Voltage 2
a
b
Fig.5
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.
Reference Voltage 2 (V2)
toff
ton
Fig.6
Assuming the charging current to be Ich and the discharging
current to be IDC ;
At charge time ;
∫ ^V1 ^–V2 ⁼
1
C
I ch dt =
I ch · ton
C
∴t on=
(V1–V2)
I ch
·
C
At discharge time
∫ ^V1^–V2 ⁼
1
C
IDC dt =
I ch · toff
C
∴t off=
(V1–V2)
IDC
·
C
Each value (typ.) of the AN8267S is ;
V1=4V
Ich=9.5µA
V2=0.95V
IDC=1.3µA
When C=1µF ;
ton=0.32s
C : External capacitor's capacity
toff=2.35s
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.
1 16 2
LHH
HLL
Polarities of Pins2, 1, and 16