For PFM version, when the load current is lower than half of the peak-to-peak inductor current in CCM, the LMR544xx operates in discontinuous conduction mode (DCM), also known as diode emulation mode (DEM). In DCM operation, the low-side switch is turned off when the inductor current drops to ILS_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.
During light load operation, pulse frequency modulation (PFM) mode is activated to maintain high efficiency operation. When either the minimum high-side switch ON time tON_MIN or the minimum peak inductor current IPEAK_MIN (300 mA 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 a significant drop in effective switching frequency.