CY28446LFXC【PDF 18/19 页】IC CLOCK CALISTOGA CK410M 64QFN

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Sheet目录1992

14页 15页 16页 17页 [18页]19页

CY28446

.......................Document #: 001-00168 Rev *F Page 8 of 19

The CY28446 requires a Parallel Resonance Crystal. Substi-

tuting a series resonance crystal causes the CY28446 to

operate at the wrong frequency and violate the ppm specifi-

cation. For most applications there is a 300-ppm frequency

shift between series and parallel crystals due to incorrect

Crystal Loading

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

mance. To realize low ppm performance, use the total capac-

itance the crystal sees to calculate the appropriate capacitive

loading (CL).

Figure 1 shows a typical crystal configuration using the two

trim capacitors. It is important that the trim capacitors are in

series with the crystal. It is not true that load capacitors are in

parallel with the crystal and are approximately equal to the

load capacitance of the crystal.

Calculating Load Capacitors

In addition to the standard external trim capacitors, consider

the trace capacitance and pin capacitance to calculate the

crystal loading correctly. Again, the capacitance on each side

Byte 8: Control Register 7

Bit

@Pup

Name

Description

Reserved

Reserved set to 0

SRC[T/C]10

SRC[T/C]10 Output Enable

0 = Disable (Tri-state), 1 = Enable

SRC[T/C]9

SRC[T/C]9 Output Enable

0 = Disable (Tri-state), 1 = Enable

SRC[T/C]8

SRC[T/C]8 Output Enable

0 = Disable (Tri-state), 1 = Enable

Reserved

Reserved set to 0

SRC10

Allow control of SRC[T/C]10 with assertion of OEA#

0 = Free running, 1 = Stopped with OEA#

SRC9

Allow control of SRC[T/C]9 with assertion of OEB#

0 = Free running, 1 = Stopped with OEB#

SRC8

Allow control of SRC[T/C]8 with assertion of OEA#

0 = Free running, 1 = Stopped with OEA#

Byte 9: Control Register 8

Bit

@Pup

Name

Description

PCI3

33-MHz Output drive strength

0 = Low, 1 = High

PCI2

33-MHz Output drive strength

0 = Low, 1 = High

PCI1

33-MHz Output drive strength

0 = Low, 1 = High

PCI0

33-MHz Output drive strength

0 = Low, 1 = High

PCIF0

33-MHz Output drive strength

0 = Low, 1 = High

Reserved

Reserved set to 1

Reserved

Reserved set to 1

Reserved

Reserved set to 1

Crystal Recommendations

Frequency

(Fund)

Cut

Loading

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

35 ppm

30 ppm

5 ppm

Figure 1. Crystal Capacitive Clarification

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