Start-up and shutdown of the LMZ20501 is controlled by the EN input. The characteristics of this input are found in Section 6.5. A valid input voltage must be present on VIN before the enable control is asserted. The maximum voltage on the EN pin is 5.5 V or V_IN, whichever is smaller. Do not allow this input to float.

The LMZ20501 features a current limit based soft start that prevents large inrush currents and output overshoots as the regulator is starting up. The peak inductor current is stepped-up in a staircase fashion during the soft start period. A typical start-up event is shown in Figure 7-4:

Figure 7-4 Typical Start-Up Waveforms, V_IN = 5 V, V_OUT = 3.3 V, I_OUT = 1 A