SL2.1A is a single 5v power supply chip. the integrated LDO(Include one 5v-3.3v LDO and one 3.3v-8v LDO) make the solution so simple.Only some capacitances needed for PCB.the chip also integrates Power-On-Reset circuit
Fully compliant with USB spec. Rev 2.0(USB 2.0) 12M crystal oscillator must be matched when using SL2.1A 5 Upstream facing port supports HS (480MHz) and FS(12MHz) modes   downstream facing ports support HS(480MHz), FS(12MHz) and LS(1.5MHz) modes. Integrated USB 2.0 Transceivers. Connected external 12MHz Crystal Oscillator is recommended for this Chip