ICS1893AF Data Sheet - Release
Chapter 6 Interface Overviews
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 ICS1893AF. 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 bypass caps serve to
adjust the final frequency of the crystal oscillation. Typical applications would use 33pF bypass caps. The
exact value will be affected by the board routing capacitance on Ref_in and Ref_out pins. Smaller bypass
capacitors raise the frequency of oscillation. Once the exact value of bypass 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 10 second
sample. Using TXCLK prevents affecting the crystal frequency by the measurement. The crystal
specification is shown in Table 6.1.
Table 6-1. 25MHz Crystal Specification
Specifications
Symbol Minimum
Typical Maximum
Unit
Fundamental Frequency
(tolerance is sum of freq.,
temp., stability and aging.)
F0
24.99875 25.00000 25.00125
MHz
Freq. Tolerance
∆F/f
CIN
50
ppm
pF
Input Capacitance
3
Table 6-2. 25MHz Oscillator Specification
Specifications
Symbol Minimum
Typical Maximum
24.99875 25.00000 25.00125
50
Unit
MHz
ppm
%
Output Frequency
F0
Freq. Stability (including aging) ∆F/f
Duty cycle CMOS level
one-half VDD
Tw/T
35
65
VIH
2.79
Volts
Volts
pS
VIL
0.33
500
Period Jitter
Input Capacitance
Tjitter
CIN
3
pF
ICS1893AF, Rev D 10/26/04
October, 2004
Copyright © 2004, Integrated Circuit Systems, Inc.
All rights reserved.
30
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