Datasheet

High-Speed Inter-Chip (HSIC) USB 2.0 Hub and Flash Media Controller
Datasheet
SMSC USB4640/USB4640i 49 Revision 1.3 (03-13-13)
DATASHEET
Chapter 5 AC Specifications
5.1 Oscillator/Crystal
Parallel Resonant, Fundamental Mode, 24 MHz ± 350 ppm.
Figure 5.1 Typical Crystal Circuit
Figure 5.2 Capacitance Formulas
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:
Capacitance Formulas. However, the PCB may present a parasitic capacitance between
XTAL1 and XTAL2. For an accurate calculation of C
1
and C
2,
take the parasitic
capacitance between traces
XTAL1 and XTAL2 into account.
Note 5.2 Each of these capacitance values is typically approximately 18 pF.
Table 5.1 Crystal Circuit Legend
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:
Capacitance Formulas (See Note 5.2)
C
2
C
1
= 2 x (C
L
– C
0
) – C
S1
C
2
= 2 x (C
L
– C
0
) – C
S2