The LM2596 is a monolithic integrated circuit that provides all the active functions for a buck switching regulator and is capable of driving a 3A load. For our project we used the S package (DDPAK/TO-263).
We chose this part because of it’s ability to reliably provide 2A in quick bursts as needed by our SIM module. It also provided a clean source of power that was regulated to an acceptable voltage for the SIM to use. We followed the reference circuit shown below. Both of the following pictures belong to SIMCom and can be found in their datasheet.