There is no limitation for small duty cycles since even at very low duty cycles, the switching frequency is reduced as needed to always ensure a proper regulation.

If the output voltage level comes close to the input voltage, the device enters 100% mode. While the high-side switch is constantly turned on, the low-side switch is switched off. The difference between V_IN and V_OUT is determined by the voltage drop across the high-side MOSFET and the DC resistance of the inductor. The minimum V_IN that is needed to maintain a specific V_OUT value is estimated as:

where

• V_IN,MIN is the minimum input voltage to maintain an output voltage
• I_OUT,MAX is the maximum output current
• R_DS(on) is the high-side FET ON-resistance
• R_L is the inductor ohmic resistance (DCR)