4.3 Reference Clock

The IS2062/64 SoC is composed of an integrated crystal oscillation function that uses a 16 MHz±10 ppm external crystal and two specified loading capacitors to provide a high quality system reference timer source. This feature is typically used to remove the initial tolerance frequency errors, which are associated with the crystal and its equivalent loading capacitance in the mass production. Frequency trim is achieved by adjusting the crystal loading capacitance through the on-chip trim capacitors (Ctrim).

The value of trimming capacitance is 200 fF (200x10-15 F) per LSb at 5-bit word and the overall adjustable clock frequency is ±40 kHz (based on the crystal with load capacitance, CL spec = 9 pF). The following figure illustrates the crystal connection of the IS2062/64 SoC with two capacitors.

Figure 4-1. CRYSTAL CONNECTION
Note:
  1. Ctrim= 200 fF * (1 to 31); Cint = 3 pF.
  2. CL= [CL1 x CL2)/(CL1+CL2)]+(Ctrim/2)+Cint (set trim value as 16, then Ctrim = 3.2 pF).
  3. For a 16 MHz crystal, in which CL= 9 pF, then the CL1 = CL2 = 9.1 pF).
  4. For CL selection, refer to the data sheet of the crystal.