ZHCSMT4C October 2021 – November 2022 LMR51420
PRODUCTION DATA
For PFM version, when the load current is lower than half of the peak-to-peak inductor current in CCM, the LMR51420 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 IZC (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 (0.3 A 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.