SMSC USB464, USB4640i Chapter 9 AC Specifications, 9.1Oscillator/Crystal, C1 = 2 x (CL – C0) – CS1, C2 = 2 x (CL – C0) – CS2, Note, Table, SYMBOL, DATASHEET, Note 9.1 C, DESCRIPTION

High Speed Inter-Chip USB 2.0 Hub and Flash Media Controller

Datasheet

Chapter 9 AC Specifications

9.1Oscillator/Crystal

Parallel Resonant, Fundamental Mode, 24 MHz ± 350 ppm.

	Figure 9.1 Typical Crystal Circuit
	Table 9.1	Crystal Circuit Legend
SYMBOL	DESCRIPTION		IN ACCORDANCE WITH
C0	Crystal shunt capacitance		Crystal manufacturer’s specification (See Note 9.1)
CL	Crystal load capacitance
CB	Total board or trace		OEM board design
	capacitance
CS	Stray capacitance		SMSC IC and OEM board design
CXTAL	XTAL pin input capacitance		SMSC IC
C1	Load capacitors installed on		Calculated values based on Figure 9.2,
	OEM board		"Capacitance Formulas" (See Note 9.2)
C2

C1 = 2 x (CL – C0) – CS1

C2 = 2 x (CL – C0) – CS2

Figure 9.2 Capacitance Formulas

Note 9.1 C0 is usually included (subtracted by the crystal manufacturer) in the specification for CL and should be set to ‘0’ for use in the calculation of the capacitance formulas in Figure 9.2, "Capacitance Formulas". However, the OEM PCB itself may present a parasitic capacitance between XTAL1 and XTAL2. For an accurate calculation of C1 and C2, take the parasitic capacitance between traces XTAL1 and XTAL2 into account.

Note 9.2 Each of these capacitance values is typically approximately 18 pF.

Revision 1.0 (06-01-09) 54 SMSC USB4640/USB4640i

DATASHEET