ICS7152A datasheet(3/10 Pages) ICST

3 / 10 page

Spread Spectrum Clock Generator

MDS 7152A A

Revision 102005

Integrated Circuit Systems, Inc.

● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com

ICS7152A

External Components

The ICS7152A requires a minimum number of external

components for proper operation.

Decoupling Capacitor

A decoupling capacitor of 0.01µF must be connected

between GND and VDD on pins 3 and 6, as close to

these pins 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 50

Ω trace (a commonly used

trace impedance) place a 27

Ω resistor in series with

the clock line, as close to the clock output pin as

possible. The nominal impedance of the clock output is

Ω.

PCB Layout Recommendations

For optimum device performance and lowest output

phase noise, the following guidelines should be

observed.

1) The 0.01µF decoupling capacitor should be mounted

on the component side of the board as close to the

VDD pin as possible. No vias should be used between

the decoupling capacitor and VDD pin. The PCB trace

to VDD pin should be kept as short as possible, as

should the PCB trace to the ground via.

2) To minimize EMI, the 27

Ω series termination resistor

(if needed) should be placed close to the clock output.

3) 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 ICS7152A. This includes signal traces

just underneath the device, or on layers adjacent to the

ground plane layer used by the device.

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) = (CL - 6) x 2

In the equation, CL 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.

Spread Spectrum Profile

The ICS7152A 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.

Time

Modulation Rate

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