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

If the output voltage (V_OUT) comes close to the input voltage (V_IN), the device enters 100% mode. While the high-side switch is constantly turned on, the low-side switch is switched off. This action is particularly useful in battery-powered applications to achieve longest operation time by taking full advantage of the whole battery voltage range. The difference between V_IN and V_OUT is determined by the voltage drop across the high-side FET 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 = Minimum input voltage to maintain an output voltage
• I_OUT,MAX = Maximum output current
• R_DS(on) = High-side FET ON-resistance
• R_L = Inductor ohmic resistance (DCR)