8.4.4 Light-Load Operation (PFM Version)

For PFM version, when the load current is lower than half of the peak-to-peak inductor current in CCM, the TPS560430 operates in Discontinuous Conduction Mode (DCM), also known as Diode Emulation Mode (DEM). In DCM operation, the LS switch is turned off when the inductor current drops to I_{LS_ZC} (20 mA typical) to improve efficiency. Both switching losses and conduction losses are reduced in DCM, compared to forced PWM operation at light load.

At even lighter current load, Pulse Frequency Modulation (PFM) mode is activated to maintain high efficiency operation. When either the minimum HS switch ON time t_{ON_MIN} or the minimum peak inductor current I_{PEAK_MIN} (150mA typical) is reached, the switching frequency decreases to maintain regulation. In PFM mode, switching frequency is decreased by the control loop to maintain output voltage regulation when load current reduces. Switching loss is further reduced in PFM operation due to less frequent switching actions.