The LM3478 device uses a fixed frequency, Pulse Width Modulated (PWM) current mode control architecture.The Functional Block Diagram shows the basic functionality. In a typical application circuit, the peak currentthrough the external MOSFET is sensed through an external sense resistor. The voltage across this resistor isfed into the ISEN pin. This voltage is fed into the positive input of the PWM comparator. The output voltage is alsosensed through an external feedback resistor divider network and fed into the error amplifier negative input(feedback pin, FB). The output of the error amplifier (COMP pin) is added to the slope compensation ramp andfed into the negative input of the PWM comparator. At the start of any switching cycle, the oscillator sets the RSlatch using the switch logic block. This forces a high signal on the DR pin (gate of the external MOSFET) and theexternal MOSFET turns on. When the voltage on the positive input of the PWM comparator exceeds the negativeinput, the RS latch is reset and the external MOSFET turns off