2-Port USB 2.0 Hi-Speed Hub Controller
Datasheet
DS00001726A-page 44
2014 Microchip Technology Inc.
Chapter 6 AC Specifications
6.1
Oscillator/Crystal
Parallel Resonant, Fundamental Mode, 24 MHz
±
350 ppm.
Figure 6.1 Typical Crystal Circuit
Table 6.1 Crystal Circuit Legend
Figure 6.2 Formula to Find the Value of C
1
and C
2
Note 6.1
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
"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 6.2
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
C
L
Crystal load capacitance
C
B
Total board or trace capacitance
OEM board design
C
S
Stray capacitance
Microchip IC and OEM board design
C
XTAL
XTAL pin input capacitance
Microchip IC
C
1
Load capacitors installed on OEM
board
Calculated values based on
Figure 6.2, "Formula to Find the
)
C
2
C
1
C
2
C
L
Crystal
C
0
XTALIN
(C
S1
= C
B1
+ C
XTALIN
)
XTALOUT
(C
S2
= C
B2
+ C
XTALOUT
)
C
1
= 2 x (C
L
–
C
0
) – C
S1
C
2
= 2 x (C
L
–
C
0
) – C
S2
