This part is a kind of semiconductor called FDZ1040L.

Function of this product has Integrated Load Switch.

Manufacturers : Fairchild Semiconductor

Image and pinout :

Some of the text within the PDF file :

FDZ1040L Integrated Load Switch April 2013 FDZ1040L Integrated Load Switch Features  Optimized for Low-Voltage Core ICs in Portable Systems  Very Small Package Dimension: WLCSP 0.8 X 0.8 X 0.5 mm3  Current = 1.2 A, VIN max = 4 V  Current = 2 A, VIN max = 4 V (Pulsed)  RDS(on) = 80 mΩ at VON = VIN = 4 V  RDS(on) = 85 mΩ at VON = VIN = 3.6 V  RDS(on) = 90 mΩ at VON = VIN = 3 V  RDS(on) = 110 mΩ at VON = 0.7 V, VIN = 1.6 V  RDS(on) = 309 mΩ at VON = 0.7 V, VIN = 1 V  RoHS Compliant Description This device is particularly suited for compact power management in portable applications needing 1 V to 4 V input and 1.2 A output current capability. This load switch integrated a level-shifting function that drives a Pchannel power MOSFET in a very small 0.8 [ ... ]

FDZ1040L PDF Datasheet Download