ICS1893CFILFT datasheet(21/126 Pages) ICST

21 / 126 page

Chapter 5 Interface Overviews

ICS1893CF, Rev. F, 03/01/07

Mar. 2007

ICS1893CF Data Sheet Rev. F - Release

If a crystal is used as the clocking source, connect it to both the Ref_in (pin 47) and Ref_out (pin 46) pins

of the ICS1893CF. A pair of bypass capacitors on either side of the crystal are connected to ground. The

crystal is used in the parallel resonance or anti-resonance mode. The value of the load caps serve to adjust

the final frequency of the crystal oscillation. Typical applications would use 33pF load caps. The exact

value will be affected by the board routing capacitance on Ref_in and Ref_out pins. Smaller load capacitors

raise the frequency of oscillation. Once the exact value of load capacitance is established it will be the

same for all boards using the same specification crystal. The best way to measure the crystal frequency is

to measure the frequency of TXCLK (pin 37) using a frequency counter with a 1 second gate time. Using

the buffered output TXCLK prevents the crystal frequency from being affected by the measurement. The

crystal specification is shown in Table 5.1.

Table 5-1. 25MHz Crystal Specification

Specifications

Symbol Minimum

Typical Maximum

Unit

Fundamental Frequency

(tolerance is sum of freq.,

temp., stability and aging.)

24.99875 25.00000

25.00125

MHz

Freq. Tolerance

∆F/f

± 50

ppm

Input Capacitance

Cin

Table 5-2. 25MHz Oscillator Specification

Specifications

Symbol Minimum

Typical Maximum

Unit

Output Frequency

24.99875 25.00000

25.00125

MHz

Freq. Stability (including aging)

∆F/f

± 50

ppm

Duty cycle CMOS level

one-half VDD

Tw/T

VIH

2.79

Volts

VIL

0.33

Volts

Period Jitter

Tjitter

500

Input Capacitance

CIN

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