FA5304AP 데이터 시트보기 (PDF) - Fuji Electric

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FA5304AP

Bipolar IC For Switching Power Supply Control

Fuji Electric 

4.2 Overload shutdown

Figure 9 shows the overload shutdown circuit, and Figure 10 is

a timing chart which illustrates overload shutdown operation.If

the output voltage drops due to an overload or short-circuit, the

output voltage of the FB pin rises. If FB pin voltage exceeds

the reference voltage (2.7V) of comparator C3, the output of

comparator C3 switches low to turn transistor Q off. In normal

operation, transistor Q is on and the CS pin is clamped at 3.6V

by zener diode Zn. With Q off, the clamp is released and the

10µA constant-current source begins to charge capacitor CS

again and the CS pin voltage rises. When the CS pin voltage

exceeds the reference voltage (7.0V) of comparator C2, the

output of comparator C2 switches high to turn the bias circuit

off. The IC then enters the latched mode and shuts the output

down. Shutdown current consumption is 400µA(VCC=9V).

This current must be supplied through the startup resistor. The

IC then discharges the MOSFET gates.

Shutdown operation initiated by an overload can be reset by

lowering supply voltage VCC below 8.7V or forcing the CS pin

voltage below 7.0V.The period tOL from the time that the output

is short-circuited to the time that the bias circuit turns off is

given by the following equation:

tOL(mS) = 340Cs(µF).........................................(3)

4.3 Overvoltage shutdown

Figure 11 shows the overvoltage shutdown circuit, and Figure

12 is a timing chart which illustrates overvoltage shutdown

operation.

The optocoupler PC1 is connected between the CS and VCC

pins. If the output voltage rises too high, the PC1 turns on to

raise the voltage at the CS pin via resistor R6. When the CS

pin voltage exceeds the reference voltage (7.0V) of

comparator C2, comparator C2 switches high to turn the bias

circuit off. The IC then enters the latched mode and shuts the

output down. The shutdown current consumption of the IC is

400µA(VCC=9V). This current must be applied via startup

resistor R5.

The IC then discharges the MOSFET gates.

The shutdown operation initiated by an overvoltage condition

can be reset by lowering supply voltage VCC below 8.7V or

forcing the CS pin voltage below 7.0V.

During normal operation, the CS pin is clamped by a 3.6V

zener diode with a sink current of 150µA max. Therefore, a

current of 150µA or more must be supplied by the optocoupler

in order to raise the CS pin voltage above 7.0V.

FA5304AP(S)/FA5305AP(S)

Fig. 9 Overload shutdown circuit

Fig. 10 Overload shutdown timing chart

Fig. 11 Overvoltage shutdown circuit

Fig. 12 Overvoltage shutdown timing chart

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