Current into output capacitor

Many switcher ICs are in fact designed with a certain minimum on-time (especially the current mode control types). They also keep to the minimum pulse width until about 0.2 to 0.3V on the feedback pin. In such cases, with a reasonably large output bulk capacitor, you will see a huge inrush of current into the output capacitor, even before the latter starts to rise appreciably. You should also be aware that inrush current into the input capacitor of any topology is very high, and no switch action can even hope to prevent that. 

Similarly, the current into the output capacitor is also choppy, because combined with the steady dc current into the load (Iout), it forms the diode current (which we know is always choppy for any topology) (see Figure 1-9). 

However, the current into the output capacitor is smooth, because it is in series with the inductor (which prevents sudden jumps in current). 

---