On and off switch, Programmable switching regulator, Switched-mode power supply

 MP2451 Series 36 V 0.6 A 2 MHz Surface Mount Step-Down Converter - SOT-23-6

https://www.futureelectronics.com/p/semiconductors--analog--regulators-reference--switching-regulators/mp2451dt-lf-z-monolithic-power-systems-2045646