Pin 1 (COMP) is the compensating pin of the error amplifier. The RC compensation network should be connected between the pin and the inverting input of the error amplifier (VFB) to improve the performance of the error amplifier.
Pin 2 (VFB) is the inverting input of the error amplifier. The feedback voltage is fed into the pin and compared with the reference voltage at the in-phase input of the error amplifier to set the error voltage.
Pin 3 (ISENSE) is the in-phase input of the current sampling comparator. The voltage drop at both ends of the current sampling resistor is applied to the pin and compared with the error voltage (maximum 1V) applied to the inverting input of the amplifier to determine the duty cycle of the output drive pulse.