While the MODE pin is pulled to VCC directly or connected to the AGND pin through a resistor larger than 121 kΩ, the device automatically reduces the switching frequency at light-load conditions to maintain high efficiency. This section describes the operation in detail.

As the output current decreases from heavy load condition, the inductor current also decreases until the rippled valley of the inductor current touches zero level. Zero level is the boundary between the continuous-conduction and discontinuous-conduction modes. The synchronous MOSFET turns off when this zero inductor current is detected. As the load current decreases further, the converter runs into discontinuous-conduction mode (DCM). The on-time is maintained to a level approximately the same as during continuous-conduction mode operation so that discharging the output capacitor with a smaller load current to the level of the reference voltage requires more time. The transition point to the light-load operation I_O(LL) (for example, the threshold between continuous- and discontinuous-conduction mode) is calculated as shown in Equation 6.

Equation 6.

where

• f_SW is the switching frequency

Using only ceramic capacitors is recommended for skip mode.