An initiator assembly that includes a housing, a base, an exploding foil initiator and an input charge assembly. The housing defines a cavity. The base coupled to the housing and closes the cavity. The exploding foil initiator is mounted to the base and has a barrel that defines an initiation axis. The input charge assembly is received in the cavity and includes a holder and an input charge. The holder has a first axial end and a second axial end that are spaced apart along the initiation axis. The first axial end is closer to an output of the barrel than the second axial end. A charge aperture is formed through the first axial end of the holder and does not extend through the second axial end of the holder. The input charge is formed of an explosive material and is received into the charge aperture.