FA8A00N / 01N Datasheet
(4) Pin No.4 (GND pin)
[Function]
Pin No. 4 serves as the basis of the voltage of each part
of the IC.
(6) Pin No.6 (VCC pin)
[Function]
(i) Supplying the power of IC
(ii) Preventing malfunction by detecting low voltage
(iii) Latch stopping at secondary-side over voltage
(iv)Short detection for secondary side
[How to use]
(5) Pin No.5 (OUT pin)
[Function]
Drives the MOSFET
[How to use]
(i) Supplying power of IC
・Connection method
・Connection method
Connect pin No.5 to the MOSFET gate through resistor
(Fig.23,Fig.24,Fig.25)
Generally, the auxiliary winding voltage provided in the
transformer is rectified/smoothed and connected.
(Fig.26). Or DC power from outside is connected.
・Operation
・Operation
While the MOSFET remains ON, it is in high state, and
VCC voltage is output.While the MOSFET remains OFF,
It is in low state, and 0 voltage is output.
If AC input voltage is applied, the capacitor of VCC is
charged by the current supplied from the start-up
circuit and the voltage increases. When the VCC
reaches the ON threshold voltage, the IC starts
operating. In the steady-state, the IC operates by
means of the voltage supplied from the auxiliary
winding.
■Advice for designing
Between the gate pin of MOSFET and OUT pin of IC,
resistor is generally inserted to adjust the switching
speed and to prevent the parasitic oscillation at gate
pin.(Fig. 23).In such a case, it may be desirable to
independently determine the driving current when
MOSFET is turned on or off.If so, connect the gate drive
circuit in Fig.24 or Fig.25 between the gate pin of
MOSFET and OUT pin of IC. In case of Fig.24, the
current is limited by R1+R2 when on or by R2 alone
when off.
VCC 6
C1 C2
In case of Fig.25, the current is limited by R1 alone
when on or it is limited by the parallel resistance of R1
and R2 when off.
Fig.26 VCC pin circuit
■Advice for designing
Since large current is fed to the VCC pin when the
MOSFET is driven, relatively large noise tends to be
generated. In addition, noise is also generated from the
current supplied by the auxiliary winding. If this noise is
large, malfunction of the IC may result. To minimize the
noise that is generated at the VCC pin, add a bypass
capacitor C2 (0.1 µF or higher) adjacent to the VCC pin
of the IC, between VCC and the GND, as shown in
Fig.26, in addition to the electrolytic capacitor. Just after
the IC starts, the VCC pin voltage decreases until the
voltage of the auxiliary winding rises enough. (Fig.27)
The capacitor C2 connected to the VCC pin should be
determined so that the voltage will not decrease to the
OFF threshold voltage in the meantime. Specifically, to
select the VCC pin capacitor so that the lower limit of the
VCC pin voltage will be 6.5V or more is recommended. If
the capacitor of the VCC pin is too small, VCC voltage
repeats up/down operation between ON and OFF
threshold voltage, and consequently the power supply
cannot be turned on. (Fig.28)
Q1
5
R
OUT
Fig.23 OUT pin drive circuit (1)
Q1
5
R1
R2
OUT
Fig.24 OUT pin drive circuit (2)
R2
Q1
5
R1
OUT
Fig.25 OUT pin drive circuit (3)
© Fuji Electric Co., Ltd. All rights reserved.
July,2016 DS-102E Rev3.0
24/30
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