The MP3429 works in a fixed-frequency PWMmode for any load condition if MODE is set high(>1.6V). In this condition, the off time isdetermined by the internal circuit to achieve the600kHz frequency based on the VIN/VOUT ratio.When the load decreases, the average inputcurrent drops, and the inductor current fromVOUT to VIN may become negative during the off-time (LS-FET is off and HS-FET is on). Thisforces the inductor current to work in continuousconduction mode (FCCM) with a fixed frequency,producing a lower VOUT ripple than in PSM