USX2064 datasheet(41/54 Pages) MICROCHIP

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2023 Microchip Technology Inc. and its subsidiaries

DS00001986E-page 41

USX2064

7.0

AC SPECIFICATIONS

7.1

Oscillator/Crystal

Crystal: Parallel resonant, fundamental mode, 24 MHz 350 ppm

External Clock: 50% duty cycle  10%, 24/48 MHz  350 ppm, jitter < 100 ps rms

Note 7-1

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 7-2. 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 7-2

Each of these capacitance values is typically around 18 pF.

FIGURE 7-1:

TYPICAL CRYSTAL CIRCUIT

TABLE 7-1:

CRYSTAL CIRCUIT LEGEND

Symbol

Description

In Accordance With

Crystal shunt capacitance

Crystal manufacturer’s specification (Note 7-1)

Crystal load capacitance

Total board or trace capacitance

OEM board design

Stray capacitance

MCHP IC and OEM board design

CXTAL

XTAL pin input capacitance

MCHP IC

Load capacitors installed on OEM

board

Calculated values based on Figure 7-2 (Note 7-2)

FIGURE 7-2:

FORMULA TO FIND THE VALUE OF C1 AND C2

1 M

Crystal

XTAL2

(CS2 = CB2 + CXTAL2 )

XTAL1

(CS1 = CB1 + CXTAL1 )

C1 = 2 x (CL – C0) – CS1

C2 = 2 x (CL – C0) – CS2

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