FA3641N 데이터 시트보기 (PDF) - Fuji Electric

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FA3641N

PWM control IC with light load power saving function For Switching Power Supply Control

Fuji Electric 

4.2 Overload shutdown function

Figure 10 shows the overload shutdown circuit, and Figure 11

is a timing chart that illustrates overload shutdown operation.

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

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

the reference voltage (3.0V) of comparator C3, the output of

comparator C3 goes low to turn off the switch. With the switch

off, the CS pin voltage clamped at 4.0V by zener diode in

normal operation is unclamped, and the constant current

source (6.5µA) begins to charge capacitor Cs again and the CS

pin voltage rises. When the CS pin voltage exceeds the

reference voltage (8.5V) of comparator C2, the output of

comparator C2 toggles to turn off the 5V REF circuit. The IC

then enters the latched mode and shuts down the output. IC

current consumption for shutdown is 45µA (typ) (Vcc = 10V).

This current must be supplied through the startup resistor. The

IC enters output off (low voltage) state.

The overload shutdown operation can be reset by lowering the

supply voltage Vcc to below the OFF threshold voltage (9.0V)

or forcing the CS pin voltage below 7.9V.

The period tOL from the time the output is short-circuited to the

time the output circuit goes off is given by the following

equation:

tOL [ms] Լ 690 ϫ Cs .................................................. (4)

Cs: Soft start capacitor [µF]

When you want to disable the overload shutdown function, see

item 11 in “Design advice”

4.3 Output ON/OFF control function

The IC can be turned on or off via an external signal applied to

the CS pin. Figure 12 shows the output on/off control circuit,

and Figure 13 is a timing chart.

The IC is turned off when the CS pin voltage is externally made

to drop below 0.68V (typ). The output of comparator C1 goes

high to turn the 5V REF circuit. This shuts the output down.

The IC enters output off (low voltage) state. Required IC

current consumption during shutdown is 100µA (typ) (Vcc =

17V). This current must be supplied through the startup

resistor. The IC goes on when the CS pin is opened and the

CS pin voltage exceeds 0.82V (typ). This turns on the 5V REF

circuit and results in automatic soft start. The power supply

then restarts operation.

FA3641P(N), FA3647P(N)

Fig. 10 Overload shutdown circuit

Fig. 11 Overload shutdown timing chart

Fig. 12 External output ON/OFF control circuit

Fig. 13 Output ON/OFF control circuit timing chart

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