View hm3420b datasheet:

 3420B Features General Description   The HM3420B is a high- efficiency monolithic synchronous  1.5MHz Constant Frequency Operation buck regulator using a constant frequency, current mode  No Schottky Diode Required architecture. The device is available in an adjustable  Low Dropout Operation:100% Duty Cycle version. Supply current with no load is 40uA and drops  PFM Mode for High Efficiency in Light Load to <1uA in shutdown. The 2.5V to 5.5 V input voltage  Over temperature Protected range makes the HM3420B ideally suited for single Li- Ion  Low Quiescent Current: 40μA battery powered applications. 100% duty cycle provides  Short Circuit Protection low dropout operation, extending battery life in portable  Inrush Cur