FA5540 Fuji Electric holdings CO.,Ltd, FA5540 Datasheet - Page 29

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

Rev.0 July-2007
(4) No.4 pin (GND pin)
Function
(5) No.5 pin (OUT pin)
Function
Usage
・Operation
・Compliment
(ⅱ) Burst operation adjustment (for FA5541/42)
・Connection
・Operation
・Compliment
This is the standard voltage for each IC.
Driving of MOSFET.
・Connection
・Operation
and CR filter is unnecessary in general.
For example, when getting into burst
operation in case of a heavy load, the output
ripple becomes bigger. If this is a problem,
this pin should be used. However the more
difficult it becomes to get into burst operation,
the more electric power consumption in
waiting increases.
through a resistor (Fig.18, Fig.19, & Fig.20).
A MOSFET current signal that is input into IS
pin is input into a current comparator. When it
gets to the threshold voltage that is
designated by FB pin, it turns off MOSFET.
The maximum threshold voltage is 1V (typ.).
MOSFET current is restricted by the current
that corresponds to this voltage (1V) even in
a transient condition at the startup or in an
abnormal condition at overload
A blanking function of 205ns (L.E.B) is built-in,
A resistor R
the current detecting resistor Rs and IS pin
(Fig. 17).
A 50μA current supply is included in IS pin of
FA5541/42, and electric current is sent out
from IS pin. The voltage that is equal to the
multiplication of the current value and the
resistor value is effective to restrain burst
operation.
This pin is connected to MOSFET gate pin
During the period MOSFET is ON, this pin is
kept in high position and almost the same
voltage as Vcc is output.
During the period MOSFET is OFF, this pin is
kept in low position and nearly zero voltage is
output.
IS
is inserted additionally between
FA5540/5541/5542
29
Driver
Driver
Driver
Comparator
Current
Fig. 17 Filter of IS pin
Fig. 18 OUT pin circuit (1)
Fig. 19 OUT pin circuit (2)
Fig. 20 OUT pin circuit (3)
6
4
6
4
6
4
VCC
GND
VCC
GND
VCC
GND
OUT
OUT
OUT
Fuji Electric Device Technology
5
5
5
50µA
IS
3
R
IS
Rs