ICS841202-245 Data Sheet CRYSTAL-TO-HCSL CLOCK SYNTHESIZER
ICS841202BK-245 REVISION A AUGUST 20, 2013 11 ©2013 Integrated Device Technology, Inc.
Application Schematic Example
Figure 4 (next page) shows an example of ICS841202-245
application schematic. The schematic example focuses on functional
connections and is not configuration specific. Refer to the pin
description and functional tables in the datasheet to ensure that the
logic control inpu ts are properly set.
A 12pF parallel resonant 25MHz crystal is used. For this device, the
cryst
al load capacitors are required for proper operation. The load
capacitance, C1 = C2 = 15pF, are recommended for frequency
accuracy. Depending on the variation of the parasitic stray capacity
of the printed circuit board traces between the crystal and the
XTAL_IN and XTAL_OUT pins, the values of C1 and C2 might require
a slight adjustment to optimize the frequency accuracy. Cry
stals with
other load capacitance specifications can be used, but this will
require adjusting C1 and C2. When designing the circuit board,
return the capacitors to ground though a single point contact close to
the package.
As with any high speed analog circuitry, the power supply pins are
vulnerable to random nois
e. To achieve optimum jitter performance,
power supply isolation is required. The ICS841202-245 provides
separate power supplies to isolate any high switching noise from
coupling into the internal PLL.
In order to achieve the best possible filtering, it is recommended that
the placement of the filter components be on the device side of the
PCB as close to the power pins as possible. If space is limited, the
0.1uF capacitor in each power pin filter s
hould be placed on the
device side. The other components can be on the opposite side of the
PCB. Power supply filter recommendations are a general guideline to
be used for reducing external noise from coupling into the devices
The filter performance is designed for a wide range of noise
frequencies. This low-pass filter starts to attenuate noise at
approximately 10kHz. a specific frequency noise component is
known, su
ch as switching power supplies frequencies, it is
recommended that component values be adjusted and if required,
additional filtering be added. Additionally, good general design
practices for power plane voltage stability suggests adding bulk
capacitance in the local area of all devices.
