June 2005

P2779A

rev 0.1

Alliance Semiconductor

2575, Augustine Drive

• Santa Clara, CA • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com

Notice: The information in this document is subject to change without notice.

Low-Cost Notebook EMI Reduction IC

Features

Provides up to 15dB of EMI suppression

FCC approved method of EMI attenuation

Generates a 1X low EMI spread spectrum clock of

the input frequency

Operates between 20MHz and 38MHz input

frequency range

External loop filter for spread percentage adjustment

Spreading ranges from ±0.25% to ±2.5%

Ultra low cycle-to-cycle jitter

Zero-Cycle slip at small deviations

3.3 V Operating Voltage

10 mA output drives

TTL or CMOS compatible outputs

Low power CMOS design

Available in 8-pin SOIC and TSSOP Packages

Available for Industrial temperature operating

range (-40º C to 85º C)

Product Description

The P2779A is a versatile spread spectrum frequency

modulator designed specifically for mobile and digital

camera and other digital video and imaging applications.

The P2779A reduces electromagnetic interference (EMI) at

the clock source, which provides system-wide reduction of

EMI of all clock dependent signals. The P2779A allows

significant system cost savings by reducing the number of

circuit board layers and shielding that are traditionally

required to pass EMI regulations.

The P2779A uses the most efficient and optimized

modulation profile approved by the FCC.

The P2779A modulates the output of a single PLL in order

to spread the bandwidth of a synthesized clock and, more

importantly, decreases the peak amplitudes of its

harmonics. This results in significantly lower system EMI

compared to the typical narrow-band signal produced by

oscillators and most frequency generators. Lowering EMI

by increasing a signal’s bandwidth is called spread

spectrum clock generation.

Applications

The P2779A is targeted toward mobile 3D graphics chip set

applications.

Block Diagram

VDD

PD

VSS

ModOUT

XIN

Frequency

Divider

Feedback

Divider

Modulation

Phase

Detector

Loop

Filter

VCO

Output

Divider

PLL

Crystal

Oscillator

XOUT

REF

LF