FA5540 Fuji Electric holdings CO.,Ltd, FA5540 Datasheet - Page 30

• Manufacturer Part Number: FA5540
• Description: Fuji Switching Power Supply Control Ic
• Manufacturer: Fuji Electric holdings CO.,Ltd

Rev.0 July-2007
・Compliment
(6) No.6 pin (VCC pin)
Function
Usage
・Operation
(ⅱ) Protection of over voltage
( ⅱ ) Detect over-voltage in primary side and
(ⅰ) Provision of power supply for IC
(ⅰ) Provision of power supply for IC
・Connection
・Connection
・Operation
・Compliment
transformer is rectified and smoothed and is
connected to this pin (Fig. 21).
provided by a startup circuit without using an
auxiliary winding but standby power
requirement becomes larger and heat
dissipation increases. Therefore it is better to
provide Vcc by an auxiliary winding for low
standby power requirement.
Provision of power supply for IC.
A gate resistor is connected to restrict current
of OUT pin and to protect oscillation of gate
pin voltage.
Output current rating of IC is 0.25A for source
and 0.5A for sink.
Generally the auxiliary winding voltage of a
In addition this auxiliary winding can also be
connected with ZCD pin.
The voltage provided by the auxiliary winding
should be set 12V to 14.5V (FA5540) / 12V to
26V (FA5541/42) in ordinary operation.
It is possible to drive IC with the current
In addition, much attention is required in
selecting MOSFET to drive, because there is
a limit to the current to be provided when IC
is driven only by a startup circuit.
Same as the connection described in (ⅰ)
If Vcc exceeds 16V (FA5540) / 28V
(FA5541/42) (typ.) and maintains more than
40µs (FA5540) / 54µs (FA5541/42) (typ.),
protection of over voltage is activated and IC
is latched.
For example, if the output voltage rises
abnormally due to the error of a feedback
circuit, also Vcc rises abnormally. When Vcc
exceeds 16V (FA5540) / 28V (FA5541/42),
latch protection is activated. Therefore that
operates as over voltage protection of
primary side detection.
activate latch protection.
FA5540/5541/5542
30
VCC
ZCD
Fig.21 VCC circuit
Fuji Electric Device Technology
6
1
C
ZCD
R
ZCD