8538BG-31LF IDT, 8538BG-31LF Datasheet - Page 7

• Manufacturer Part Number: 8538BG-31LF
• Description: Clock Drivers & Distribution
• Manufacturer: IDT

Specifications of 8538BG-31LF

• Product Category: Clock Drivers & Distribution
• Rohs: yes
• Part # Aliases: ICS8538BG-31LF

Application Information
Crystal Input Interface
The ICS8538-31 has been characterized with 18pF parallel
resonant crystals. The capacitor values, C1 and C2, shown in
Figure 2 below were determined using an 18pF parallel resonant
crystal and were chosen to minimize the ppm error. These same
Figure 2. Crystal Input Interface
LVCMOS to XTAL Interface
The XTAL_IN input can accept a single-ended LVCMOS signal
through an AC coupling capacitor. A general interface diagram is
shown in Figure 3. The XTAL_OUT pin can be left floating. The
input edge rate can be as slow as 10ns. For LVCMOS inputs, it is
recommended that the amplitude be reduced from full swing to half
swing in order to prevent signal interference with the power rail and
to reduce noise. This configuration requires that the output
Figure 3. General Diagram for LVCMOS Driver to XTAL Input Interface
IDT™ / ICS™ LVPECL FANOUT BUFFER
ICS8538-31
LOW SKEW, 1-TO-8, CRYSTAL OSCILLATOR/LVCMOS-TO-3.3V LVPECL FANOUT BUFFER
18pF Parallel Crystal
V
CC
Ro
X1
Rs
Zo = Ro + Rs
50
C1
18p
C2
22p
XTAL_IN
XTAL_OUT
V
CC
R1
R2
0.1µf
XTAL_IN
XTAL_OUT
7
capacitor values will tune any 18pF parallel resonant crystal over
the frequency range and other parameters specified in this data
sheet. The optimum C1 and C2 values can be slightly adjusted for
different board layouts.
impedance of the driver (Ro) plus the series resistance (Rs) equals
the transmission line impedance. In addition, matched termination
at the crystal input will attenuate the signal in half. This can be
done in one of two ways. First, R1 and R2 in parallel should equal
the transmission line impedance. For most 50Ω applications, R1
and R2 can be 100Ω. This can also be accomplished by removing
R1 and making R2 50Ω.
ICS8538BG-31 REV. B FEBRUARY 5, 2008