8535AGI-31LFT IDT, 8535AGI-31LFT Datasheet - Page 9

• Manufacturer Part Number: 8535AGI-31LFT
• Description: Clock Drivers & Distribution 1
• Manufacturer: IDT

Specifications of 8535AGI-31LFT

• Rohs: yes
• Part # Aliases: ICS8535AGI-31LFT

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 signals, 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
impedance of the driver (Ro) plus the series resistance (Rs) equals
Figure 3. General Diagram for LVCMOS Driver to XTAL Input Interface
Termination for 3.3V LVPECL Outputs
The clock layout topology shown below is a typical termination for
LVPECL outputs. The two different layouts mentioned are
recommended only as guidelines.
The differential outputs are low impedance follower outputs that
generate ECL/LVPECL compatible outputs. Therefore, terminating
resistors (DC current path to ground) or current sources must be
used for functionality. These outputs are designed to drive 50Ω
Figure 4A. 3.3V LVPECL Output Termination
ICS8535I-31
ICS8535AGI-31 REVISION A JANUARY 27, 2010
RTT =
V
CC
Ro
((V
3.3V
OH
LVPECL
+ V
OL
) / (V
1
Rs
Zo = Ro + Rs
CC
Z
Z
– 2)) – 2
o
o
= 50
= 50
* Z
50
R1
50
o
RTT
R2
50
V
CC
R1
R2
V
+
_
CC
3.3V
0.1µf
- 2V
Input
XTAL_IN
XTAL_OUT
LOW SKEW, 1-TO-4, CRYSTAL OSCILLATOR/LVCMOS-TO-3.3V LVPECL FANOUT BUFFER
9
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. By overdriving the crystal oscillator, the device will
be functional, but note, the device performance is guaranteed by
using a quartz crystal.
transmission lines. Matched impedance techniques should be used
to maximize operating frequency and minimize signal distortion.
Figures 4A and 4B show two different layouts which are
recommended only as guidelines. Other suitable clock layouts may
exist and it would be recommended that the board designers simulate
to guarantee compatibility across all printed circuit and clock
component process variations.
Figure 4B. 3.3V LVPECL Output Termination
3.3V
LVPECL
Z
Z
o
o
= 50
= 50
R3
125
©2010 Integrated Device Technology, Inc.
R1
84
3.3V
R4
125
R2
84
+
_
3.3V
Input