FA5304AP 데이터 시트보기 (PDF) - Collmer Semiconductor

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FA5304AP

Bipolar IC For Switching Power Supply Control

Collmer Semiconductor 

FA5304AP(S)/FA5305AP(S)

4.4 Output ON/OFF control

The IC can be turned on and off by an external signal applied to

the CS pin.

Figure 13 shows the external output on/off control circuit, and

Figure 14 is the timing chart.

The IC is turned off if the CS pin voltage falls below 0.42V. The

output of comparator C1 switches high to turn the bias circuit

off. This shuts the output down. The IC then discharges the

MOSFET gates.

The IC turns on if the CS pin is opened for automatic soft start.

The power supply then restarts operation.

5. Overcurrent limiting circuit

The overcurrent limiting circuit detects the peak value of every

drain current pulse of the main switching MOSFET to limit the

overcurrent.

The detection threshold is +0.24V for FA5304A with respect to

ground as shown in Figure 15.

The drain current of the MOSFET is converted to voltage by

resistor R7 and fed to the IS pin of the IC. If the voltage exceeds

the reference voltage (0.24V) of comparator C4, the output of

comparator C4 goes high to set flip-flop output Q high. The

output is immediately turned off to shut off the current. Flip-flop

output Q is reset on the next cycle by the output of the PWM

comparator to turn the output on again. This operation is

repeated to limit the overcurrent.

If the overcurrent limiting circuit malfunctions due to noise,

place an RC filter between the IS pin and the MOSFET.

Figure 16 is a timing chart which illustrates current-limiting

operations.

Fig. 13 External output on/off control circuit

Fig. 14 Timing chart for external output on/off control

Fig. 15 Overcurrent limiting circuit for FA5304A

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Fig. 16 Overcurrent timing chart for FA5304A

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