USB2422 datasheet(38/47 Pages) MICROCHIP

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USB2422

DS00001726B-page 38

 2013 - 2015 Microchip Technology Inc.

6.0

AC SPECIFICATIONS

6.1

Oscillator/Crystal

Parallel Resonant, Fundamental Mode, 24 MHz

±350 ppm.

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.

FIGURE 6-1:

TYPICAL CRYSTAL CIRCUIT

TABLE 6-1:

CRYSTAL CIRCUIT LEGEND

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

Microchip IC and OEM board design

CXTAL

XTAL pin input capacitance

Microchip 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)

FIGURE 6-2:

FORMULA TO FIND THE VALUE OF C1 AND C2

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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