The SG3525 is a PWM-based IC. It is commonly used for controlling and switching the power supplies. One of the important feature of this IC is its shutdown function, which is controlled through the pin number 10. This pin is allows the IC’s output to be turned off quickly when needed. When a high voltage is applied to the pin number 10 and the IC’s internal PWM latch is set and the output signals are immediately disabled. The soft-start capacitor (connected to pin 8) which is normally helps the output voltage rise gradually during startup. At the same time begins to discharge through a small 150µA current source.
This allows the IC to shut down smoothly and prevents the sudden power spikes. As long as the high voltage remains on the pin 10 of the Ic. The output stays off and the soft-start capacitor continues to discharge. Once the shutdown signal is removed, the soft-start capacitor begins to charge again and the output resumes operation gradually. just like during a normal startup. Although you can also disable the output by pulling pin 8 (soft-start) or pin 9 (compensation) low, this method is slower and less effective than using the dedicated shutdown pin. To avoid accidental shutdowns due to electrical noise, it’s common to connect pin 10 to ground using a pull-down resistor and pin stays low when not actively driven high.
