USB2422 Datasheet, PDF (44/51 Pages) SMSC Corporation – 2-Port USB 2.0 Hi-Speed Hub Controller

2-Port USB 2.0 Hi-Speed Hub Controller
Datasheet
Chapter 6 AC Specifications
6.1
Oscillator/Crystal
Parallel Resonant, Fundamental Mode, 24 MHz ±350 ppm.
XTALIN
(C_S1 = C_B1 + C_XTALIN)
C₁
C₀
Crystal _CL
C₂
XTALOUT
(C_S2 = C_B2 + C_XTALOUT)
Figure 6.1 Typical Crystal Circuit
SYMBOL
C₀
C_L
C_B
C_S
C_XTAL
C₁
C₂
Table 6.1 Crystal Circuit Legend
DESCRIPTION
IN ACCORDANCE WITH
Crystal shunt capacitance
Crystal load capacitance
Total board or trace capacitance
Stray capacitance
XTAL pin input capacitance
Load capacitors installed on OEM
board
Crystal manufacturer’s specification (See Note 6.1)
OEM board design
SMSC IC and OEM board design
SMSC IC
Calculated values based on Figure 6.2, "Formula to Find the
Value of C1 and C2" (See Note 6.2)
C₁ = 2 x (C_L – C₀) – C_S1
Note 6.1
Note 6.2
C₂ = 2 x (C_L – C₀) – C_S2
Figure 6.2 Formula to Find the Value of C₁ and C₂
C₀ is usually included (subtracted by the crystal manufacturer) in the specification for C_L
and should be set to 0 for use in the calculation of the capacitance formulas in Figure 6.2,
"Formula to Find the Value of C1 and C2". However, the PCB itself may present a parasitic
capacitance between XTALIN and XTALOUT. For an accurate calculation of C₁ and C_2,
take the parasitic capacitance between traces XTALIN and XTALOUT into account.
Each of these capacitance values is typically approximately 18 pF.
Revision 1.0 (06-04-13)
44
DATASHEET
SMSC USB2422