PCM is a popular fixed-frequency control topology for DC/DC converters given its overload protection, accuracy and ease of compensation. The power stage consists of the power switches and output filter. The compensation block includes the output voltage divider network, error amplifier, reference voltage and compensation components. The pulse-width modulator uses a comparator to compare the inductor current information with the slope compensation ramp to the error signal, creating an output pulse-train that has a width controllable by the level of the error signal.

The internal clock initiates one pulse, and the high-side field-effect transistor (FET) turns on, with current increasing in the inductor. When the sensed current reaches the control voltage, the high-side FET turns off and the low-side FET turns on until the next rising edge of the clock. The next PWM pulse is generated at the next clock pulse. Thus, the switching frequency depending on the clock is truly fixed. which is convenient when designing the output filter for low electromagnetic interference (EMI).