ICS8536AG Datasheet, PDF(11/21 Page) Integrated Device Technology – Low Skew, 1-to-6, Crystal LVCMOS Differential-to-3.3V, 2.5V LVPECL Fanout Buffer

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ICS8536AG Datasheet, PDF (11/21 Pages) Integrated Device Technology – Low Skew, 1-to-6, Crystal LVCMOS Differential-to-3.3V, 2.5V LVPECL Fanout Buffer

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ICS8536-01 Data Sheet

CRYSTAL/LVCMOS/DIFFERENTIAL-TO-LVPECL FANOUT BUFFER

OVERDRIVING THE CRYSTAL INTERFACE

The XTAL_IN input can be overdriven by an LVCMOS driver or

by one side of a differential driver through an AC coupling

capacitor. The XTAL_OUT pin can be left floating. The ampli-

tude of the input signal should be between 500mV and 1.8V

and the slew rate should not be less than 2V/nS. For 3.3V

LVCMOS inputs, the amplitude must be reduced from full swing

to at least half the swing in order to prevent signal interference

with the power rail and to reduce internal noise. Figure 3 shows

an example of the interface diagram for a high speed 3.3V

LVCMOS driver. This configuration requires that the sum of the

output impedance of the driver (Ro) and 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 imped-

ance. For most 50Î© applications, R1 and R2 can be 100Î©. This

can also be accomplished by removing R1 and changing R2 to

50Î©. The values of the resistors can be increased to reduce the

loading for slower and weaker LVCMOS driver. Figure 3 shows

an example of the interface diagram for an LVPECL driver. This

is a standard LVPECL termination with one side of the driver

feeding the XTAL_IN input. It is recommended that all compo-

nents in the schematics be placed in the layout. Though some

components might not be used, they can be utilized for debug-

ging purposes. The datasheet specifications are characterized

and guaranteed by using a quartz crystal as the input.

VCC

100

Zo = 50 ohms

Zo = Ro + Rs

100

LVCMOS Driver

XTAL_OUT

XTAL_IN

.1uf

FIGURE 3A. GENERAL DIAGRAM FOR LVCMOS DRIVER TO XTAL INPUT INTERFACE

XTAL_OUT

Zo = 50 ohms

LVPECL Driver

XTAL_IN

.1uf

FIGURE 3B. GENERAL DIAGRAM FOR LVPECL DRIVER TO XTAL INPUT INTERFACE

ICS8536AG-01 REVISION B AUGUST 17, 2012

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