USB82640 datasheet(50/64 Pages) MICROCHIP

50 / 64 page

USB82640

DS60001312A-page 50

 2010-2015 Microchip Technology Inc.

9.0

AC SPECIFICATIONS

9.1

Oscillator/Clock

Parallel Resonant, Fundamental Mode, 24 MHz

± 350 ppm.

TABLE 9-1:

CRYSTAL CIRCUIT LEGEND

Note 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 cal-

culation of C1 and C2, take the parasitic capacitance between traces XTAL1 and XTAL2 into account.

2: Each of these capacitance values is typically approximately 18 pF.

FIGURE 9-1:

TYPICAL CRYSTAL CIRCUIT

Symbol

Description

In Accordance With

Crystal shunt capacitance

Crystal manufacturer’s specification (see Note 1)

Crystal load capacitance

Total board or trace capacitance

OEM board design

Stray capacitance

Microchip IC and OEM board design

CXTAL

XTAL pin input capacitance

Microchip IC

Load capacitors installed on OEM board

Calculated values based on Figure 9-2, "Capacitance

Formulas" (see Note 2)

FIGURE 9-2:

CAPACITANCE FORMULAS

C 1 = 2 x ( C L – C 0 ) – C S1

C 2 = 2 x ( C L – C 0 ) – C S2

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