Pin 1 is the output end of the error amplifier, which controls the gain of the error amplifier through the feedback network with the indirect resistance-capacitance element of pin 2.
Pin 2 is the inverse-phase input of the error amplifier. It serves as the input of sampling feedback. After collecting the output voltage, input it to this pin, and then adjust the output pulse width to control the output voltage or current after comparison.
Pin 3 is the current detection input, which detects the current flowing through the switch tube by collecting the voltage connected to the current sampling resistor in the switch tube loop. When the current rises, the voltage on the sampling resistance rises, and when it rises to a certain value (1V), the chip will turn off the output and protect the switch tube and other peripheral circuits;
Pin 4 is the timing end of the internal oscillator. Through the parameters of the resistance-capacitance element connected to this pin, the oscillation frequency of the chip is changed. When in use, the timing resistor is connected to this pin after grounding, the timing capacitor is connected to this pin, and the other end is connected to the reference voltage;
Pin 5 is the grounding terminal;
Pin 6 drives the signal output of the external switching tube, and this pin drives the signal output, which is used to control the on-off and cutoff of the external switching tube. The totem pole structure composed of the transistor is inside the chip, which can effectively improve the driving capability;
Pin 7 is the power supply end;
Pin 8 is the internal voltage reference output end of the chip, it can output a 5V reference voltage, can provide a voltage reference to the external circuit, and has a certain load capacity, can supply power to the small power components in the external circuit.