FA5540 Fuji Electric holdings CO.,Ltd, FA5540 Datasheet - Page 28

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

Rev.0 July-2007
(2) No.2 pin (FB pin)
Function
Usage
Function
Usage
(3) No.3 pin (IS pin)
・Operation
(ⅰ) Input of a feed-back signal from secondary
(ⅱ) Detection of an overload condition.
(ⅰ) Input of a feedback signal
・Connection
(ⅱ) Detection of overload
・Connection
・Operation
(ⅰ) Detection of MOSFET current
(ⅱ) Suppression of a burst operation at light load
(ⅰ) Current detection
・Connection
・Complement
input into a current comparator and finally
gives the threshold voltage for MOSFET
current signal that is detected on IS pin.
lower than the set value in an overload
condition, FB pin voltage rises and scales out.
This state is detected and judged as an
overload condition. The threshold voltage to
detect an overload is 3.3V (typ).
overload condition and automatically restarts
if the overload condition is removed. Refer to
pages 23-24 for detail operation.
condition and goes into latch mode to
maintain this condition. Refer to page 25 for
detail operation.
This pin is connected with the receiver unit of
a photo coupler. Concurrently it is connected
a capacitor in parallel with the photo coupler
to protect noise. (Fig. 15)
This pin is biased by an IC internal power
supply through a diode and a resistor.
The FB pin voltage is level-shifted and is
If the output voltage of a power supply drops
FA5540/41 operates intermittently in an
FA5542 stops switching in an overload
Connect a current detecting resistor Rs
between a source pin of MOSFET and GNC.
Input The current signal that arises in the
MOSFET is input to this resistor (Fig.16).
error-amplifier.
Same as (ⅰ) Input of the feed back signal.
FA5540/5541/5542
28
Comparator
Current
Unnecessary for FA5540
Fig. 15 FB pin circuit
Fig. 16 IS pin circuit
5V
Fuji Electric Device Technology
20kΩ
50µA
FB
2
IS
3
Rs