The TUSB73x0 supports an external oscillator source or a crystal unit. The frequency of the clock source may be 24 MHz or 48 MHz. If a clock is provided to XI instead of a crystal, XO is left open and VSSOSC should be connected to the PCB ground plane. Otherwise, if a crystal is used, the connection needs to follow the guidelines below.

Because XI and XO are coupled to other leads and supplies on the PCB, it is important to keep them as short as possible and away from any switching leads. It is also recommended to minimize the capacitance between XI and XO. This can be accomplished by connecting the VSSOSC lead to the two external capacitors CL1 and CL2 and shielding them with the clean ground lines. The VSSOSC should not be connected to PCB ground when using a crystal.

Load capacitance (C_load) of the crystal varying with the crystal vendors is the total capacitance value of the entire oscillation circuit system as seen from the crystal. It includes two external capacitors CL1 and CL2.

Figure 6-1 Oscillation Circuit