CY28405-2 datasheet(7/48 Pages) SPECTRALINEAR

7 / 48 page

CY28405-2

Rev 1.0, November 22, 2006

Page 7 of 16

Crystal Recommendations

The CY28405-2 requires a Parallel Resonance Crystal.

Substituting a series resonance crystal will cause the

CY28405-2 to operate at the wrong frequency and violate the

ppm specification. For most applications there is a 300-ppm

frequency shift between series and parallel crystals due to

incorrect loading.

Crystal Loading

Crystal loading plays a critical role in achieving low ppm perfor-

mance. To realize low ppm performance, the total capacitance

the crystal will see must be considered to calculate the appro-

priate capacitive loading (CL).

The following diagram shows a typical crystal configuration

using the two trim capacitors. An important clarification for the

following discussion is that the trim capacitors are in series

with the crystal not parallel. It’s a common misconception that

load capacitors are in parallel with the crystal and should be

approximately equal to the load capacitance of the crystal.

This is not true.

PCIF

PCI

3V66

SRCT,SRCC

CPUT_ITP,CPUC_ITP

Spread Spectrum Enable

0 = Spread Off, 1 = Spread On

REF_1

REF_1 Output Enable

0 = Disabled, 1 = Enabled

REF_0

REF_0 Output Enable

0 = Disabled, 1 = Enabled

Byte 7: Control Register

Bit

@Pup

Name

Description

Revision ID Bit 3

Revision ID Bit 2

Revision ID Bit 1

Revision ID Bit 0

Vendor ID Bit 3

Vendor ID Bit 2

Vendor ID Bit 1

Vendor ID Bit 0

Byte 6: Control Register (continued)

Bit

@Pup

Name

Description

Table 6. Crystal Recommendations

Frequency

(Fund)

Cut

Load Cap

Drive

(max.)

Shunt Cap

(max.)

Motional

(max.)

Tolerance

(max.)

Stability

(max.)

Aging

(max.)

14.31818 MHz

Parallel

20 pF

0.1 mW

5 pF

0.016 pF

50 ppm

5 ppm

Figure 1. Crystal Capacitive Clarification

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