July 2005

P2781/82/84

rev 1.5

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.

General Purpose EMI Reduction IC

Features

Provides up to 15dB of EMI suppression

FCC approved method of EMI attenuation

Generates a 1X, 2X, and 4X low EMI spread

spectrum clock of the input frequency

Input frequency range from 3 to 78MHz

External loop filter for spread % adjustment

Spreading ranges from ±0.25% to ±5.0%

Ultra low cycle-to-cycle jitter

Zero-cycle slip

3.3V operating voltage range

10 mA output drives

TTL or CMOS compatible outputs

Ultra-low power CMOS design

P278XA is available in 8 pin SOIC and TSSOP

Packages

Available for industrial and automotive

temperature ranges.

Product Description

The P278xA is a versatile spread spectrum frequency

modulator designed specifically for digital camera and

other digital video and imaging applications. The P278xA

reduces electromagnetic interference (EMI) at the clock

source, which provides system wide reduction of EMI of

all clock dependent signals. The P278xA allows

significant system cost savings by reducing the number of

circuit board layers and shielding that are traditionally

required to pass EMI regulations.

The P278xA uses the most efficient and optimized

modulation profile approved by the FCC. The P278xA

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 P278xA is targeted towards MFP, xDSL, fax modem,

set-top box, USB controller, DSC, and embedded systems.

Block Diagram

Crystal

Oscillator

Frequency

Divider

Feedback

Divider

Phase

Detector

Modulation

Output

Divider

VCO

XIN /CLKIN

XOUT

FS0

FS1

LF

VDD

VSS

PLL

ModOUT