The following operating description of the LMR16030 will refer to the Functional Block Diagram and to the waveforms in Figure 7-1. The LMR16030 output voltage is regulated by turning on the high-side N-MOSFET with controlled ON time. During high-side switch ON time, the SW pin voltage swings up to approximately V_IN, and the inductor current i_L increases with alinear slope (V_IN – V_OUT) / L. When the high-side switch is off, inductor current discharges through a freewheel diode with a slope of –V_OUT / L. The control parameter of the buck converter is defined as Duty Cycle D = t_ON / T_SW, where t_ON is the high-side switch ON time and T_SW is the switching period. The regulator control loop maintains a constant output voltage by adjusting the duty cycle D. In an ideal buck converter where losses are ignored, D is proportional to the output voltage and inversely proportional to the input voltage: D = V_OUT / V_IN.

Figure 7-1 SW Node and Inductor Current Waveforms in Continuous Conduction Mode (CCM)

The LMR16030 employs fixed-frequency peak current mode control. A voltage feedback loop is used to get accurate DC voltage regulation by adjusting the peak current command based on voltage offset. The peak inductor current is sensed from the high-side switch and compared to the peak current to control the ON time of the high-side switch. The voltage feedback loop is internally compensated, which allows for fewer external components, makes it easy to design, and provides stable operation with almost any combination of output capacitors. The regulator operates with fixed switching frequency at normal load condition. At very light load, the LMR16030 operates in sleep mode to maintain high efficiency and the switching frequency decreases with reduced load current.