In continuous conduction mode (CCM), the LM61430-Q1 supplies a regulated output voltage by turning on the internal high-side (HS) and low-side (LS) NMOS switches with varying duty cycle (D). During the HS switch on-time, the SW pin voltage, V_SW, swings up to approximately V_IN, and the inductor current, i_L, increases with a linear slope. The HS switch is turned off by the control logic as shown in Section 8.2. During the HS switch off time, t_OFF, the LS switch is turned on. Inductor current discharges through the LS switch, which forces the V_SW to swing below ground by the voltage drop across the LS switch. Refer to the waveforms in Figure 8-17. The converter loop adjusts the duty cycle to maintain a constant output voltage. D is defined by the on time of the HS switch over the switching period:

In an ideal buck converter where losses are ignored, D is proportional to the output voltage and inversely proportional to the input voltage:

Figure 8-17 SW Voltage and Inductor Current Waveforms in Continuous Conduction Mode (CCM)