USB2422 datasheet(44/51 Pages) SMSC

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2-Port USB 2.0 Hi-Speed Hub Controller

Datasheet

Revision 1.0 (06-04-13)

SMSC USB2422

DATASHEET

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 C1 and C2

Note 6.1

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 6.2,

"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 C1 and C2,

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

Crystal shunt capacitance

Crystal manufacturer’s specification (See Note 6.1)

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 6.2, "Formula to Find the

Value of C1 and C2" (See Note 6.2)

Crystal

XTALIN

(CS1 = CB1 + CXTALIN)

XTALOUT

(CS2 = CB2 + CXTALOUT)

C1 = 2 x (CL – C0) – CS1

C2 = 2 x (CL – C0) – CS2

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