Datasheet

2-Port USB 2.0 Hi-Speed Hub Controller
Datasheet
Revision 1.3 (12-27-11) 20 SMSC USB2412
DATASHEET
Chapter 5 AC Specifications
5.1 Oscillator/Crystal
Parallel Resonant, Fundamental Mode, 24 MHz ± 350 ppm.
Figure 5.1 Typical Crystal Circuit
Table 5.1 Crystal Circuit Legend
Figure 5.2 Formula to Find the Value of C
1
and C
2
Note 5.1 C
0
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 5.2,
"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 C
1
and C
2,
take the parasitic capacitance between traces XTALIN and XTALOUT into account.
Note 5.2 Each of these capacitance values is typically approximately 18 pF.
SYMBOL DESCRIPTION IN ACCORDANCE WITH
C
0
Crystal shunt capacitance
Crystal manufacturer’s specification (See Note 5.1)
C
L
Crystal load capacitance
C
B
Total board or trace capacitance OEM board design
C
S
Stray capacitance SMSC IC and OEM board design
C
XTAL
XTAL pin input capacitance SMSC IC
C
1
Load capacitors installed on OEM
board
Calculated values based on Figure 5.2, "Formula to Find the
Value of C1 and C2" (See Note 5.2)
C
2
C
1
C
2
C
L
1 M
Crystal
XTALOUT
(C
S2 =
C
B2
+ C
XTAL2
)
XTALIN
(C
S1 =
C
B1
+ C
XTAL1
)
C
0
C
1
= 2 x (C
L
– C
0
) – C
S1
C
2
= 2 x (C
L
– C
0
) – C
S2