USB4640 datasheet(53/64 Pages) SMSC

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

Datasheet

SMSC USB4640/USB4640i

Revision 1.0 (06-09-09)

DATASHEET

Chapter 9 AC Specifications

9.1

Oscillator/Crystal

Parallel Resonant, Fundamental Mode, 24 MHz

± 350 ppm.

Figure 9.1 Typical Crystal Circuit

Table 9.1 Crystal Circuit Legend

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.

SYMBOL

DESCRIPTION

IN ACCORDANCE WITH

Crystal shunt capacitance

Crystal manufacturer’s specification (See Note 9.1)

Crystal load capacitance

Total board or trace

capacitance

OEM board design

Stray capacitance

SMSC IC and OEM board design

CXTAL

XTAL pin input capacitance

SMSC IC

Load capacitors installed on

OEM board

Calculated values based on Figure 9.2,

"Capacitance Formulas" (See Note 9.2)

C1 = 2 x (CL – C0) – CS1

C2 = 2 x (CL – C0) – CS2

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