ICS7152
Spread Spectrum Clock Generator
External Components
The ICS7152 requires a minimum number of external
components for proper operation.
Crystal Information
The crystal used should be a fundamental mode,
parallel resonant. Crystal capacitors should be
connected from pins X1 to ground and X2 to ground to
optimize the initial accuracy. The value of these
capacitors is given by the following equation:
Crystal caps (pF) = (C
L
- 6) x 2
In the equation, C
L
is the crystal load capacitance. So,
for a crystal with a 16 pF load capacitance, two 20 pF
[(16-6) x 2] capacitors should be used.
Decoupling Capacitor
A decoupling capacitor of 0.01µF must be connected
between GND and VDD on pin 6, as close to this pin as
possible. For optimum device performance, the
decoupling capacitor should be mounted on the
component side of the PCB. Avoid the use of vias in the
decoupling circuit.
Series Termination Resistor
Series termination should be used on the clock output.
To series terminate a 50Ω trace (a commonly used
trace impedance) place a 27Ω resistor in series with
the clock line, as close to the clock output pin as
possible. The nominal impedance of the clock output is
25Ω.
Spread Spectrum Profile
The ICS7152 low EMI clock generator uses a triangular
frequency modulation profile for optimal down stream
tracking of zero delay buffers and other PLL devices.
The frequency modulation amplitude is constant with
variations of the input frequency.
PCB Layout Recommendations
For optimum device performance and lowest output
phase noise, the following guidelines should be
observed.
1) An optimum layout is one with all components on the
same side of the board, minimizing vias through other
signal layers. Other signal traces should be routed
away from the ICS7152. This includes signal traces just
underneath the device, or on layers adjacent to the
ground plane layer used by the device.
Frequency
Modulation Rate
Time
MDS 7152 E
Integrated Circuit Systems, Inc.
●
3
525 Race Street, San Jose, CA 95126
●
Revision 012306
tel (408) 297-1201
●
www.icst.com
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