The following operating description of the TPS2586x-Q1 refers to the Functional Block Diagram.
The TPS2586x-Q1 integrates a monolithic, synchronous, rectified, step-down, switch-mode converter with internal power MOSFETs and USB current-limit switches with charging ports auto-detection. The TPS2586x-Q1 offers a compact solution that achieves up to 5 A of continuous output current with excellent load and line regulation over a wide input supply range. The TPS2586x-Q1 supplies a regulated output voltage by turning on the high-side (HS) and low-side (LS) NMOS switches with controlled duty cycle. During high-side switch ON time, the SW pin voltage swings up to approximately V_IN. The inductor current, i_L, increases with linear slope (V_IN – V_OUT ) / L. When the HS switch is turned off by the control logic, the LS switch is turned on after an anti-shoot-through dead time. Inductor current discharges through the LS switch with a slope of –V_OUT / L. The control parameter of a 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, shown in Figure 10-2. 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 10-2 SW Node and Inductor Current Waveforms in Continuous Conduction Mode (CCM)

The TPS2586x-Q1 operates in a fixed-frequency, peak-current-mode control to regulate the output voltage. 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 threshold to control the ON time of the high-side switch. The voltage feedback loop is internally compensated, which allows for fewer external components, making it easy to design, and provides stable operation with a reasonable combination of output capacitors. The TPS2586x-Q1 operates in FPWM mode for low output voltage ripple, tight output voltage regulation, and constant switching frequency.