Some of Renesas' buck-boost devices operate in both pulse width modulation (PWM) mode and in pulse frequency modulation (PFM) mode. Why have two modes of operation? PFM mode has better efficiency at light loads while PWM mode is more efficient at higher current loads. The crossover point is approximately 350 mA. Since the Renesas buck-boost devices auto-switch between PFM and PWM modes, the devices are able to optimize the overall efficiency of the device regardless of the load.