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CS2100-OTP
12
DS841F2
example of how to determine the range of RefClk frequencies around 12 MHz to be used in order to
achieve the lowest jitter PLL output at a frequency of 12.288 MHz is as follows:
where:
and
5.2.2
Crystal Connections (XTI and XTO)
An external crystal may be used to generate RefClk. To accomplish this, a 20 pF fundamental mode par-
allel resonant crystal must be connected between the XTI and XTO pins as shown in
Figure 9. As shown,
nothing other than the crystal and its load capacitors should be connected to XTI and XTO. Please refer
5.2.3
External Reference Clock (REF_CLK)
For operation with an externally generated REF_CLK signal, XTI/REF_CLK should be connected to the
reference clock source and XTO should be left unconnected or terminated through a 47 k
Ω resistor to
GND.
5.3
Frequency Reference Clock Input, CLK_IN
The frequency reference clock input (CLK_IN) is used by the Digital PLL and Fractional-N Logic block to
on page 10). The Digital PLL first compares the CLK_IN frequency to the PLL output. The Fractional-N logic
block then translates the desired ratio based off of CLK_IN to one based off of the internal timing reference
Referenced Control
Parameter Definition
-80
-60
-40
-20
0
20
40
60
80
20
40
60
80
100
120
140
160
180
Normalized REF__CLK Frequency (kHz)
T
y
p
ica
lB
a
s
e
B
a
n
d
Ji
tt
er
(p
s
e
c
)
CLK__OUT Jitter
-15 kHz
+15 kHz
CLK__OUT
f
*32/N
Figure 8. REF_CLK Frequency vs. a Fixed CLK_OUT
f
L
f
RefClk
f
H
≤≤
f
L
f
CLK_OUT
31
32
------
15kHz
+
×
=
12.288MHz
0.96875
15kHz
+
×
=
11.919MHz
=
f
H
f
CLK_OUT
32
------
15kHz
–
×
=
12.288MHz
115kHz
+
×
=
12.273MHz
=
XTI
XTO
40 pF
Figure 9. External Component Requirements for Crystal Circuit