The TPS566231 and TPS566231P operate in advanced Eco-mode mode, which maintains high light-load efficiency. As the output current decreases from heavy load conditions, the inductor current is also reduced and eventually the rippled valley touches zero level. This is the boundary between continuous conduction and discontinuous conduction modes. The rectifying MOSFET is turned off when the zero inductor current is detected. As the load current further decreases, the converter runs into discontinuous conduction mode. The on-time is kept almost the same as it was in continuous conduction mode so that it takes longer time to discharge the output capacitor with smaller load current to the level of the reference voltage. This makes the switching frequency lower, proportional to the load current, and keeps the light load efficiency high. Use Equation 3 to calculate the light load current where the transition to Eco-mode operation happens (I_OUT(LL)).

Equation 3.

After identifying the application requirements, design the output inductance (L_OUT) so that the inductor peak-to-peak ripple current is approximately 20% to 30% of I_OUT(max) (peak current in the application). Make sure to size the inductor properly so that the valley current does not hit the negative low-side current limit.