September 2005

ASM3P2879A

rev 1.4

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 Power Peak Reducing EMI Solution

Features

Generates an EMI optimized clock signal at the

output.

Integrated loop filter components.

Operates with a 3.3V /2.5V Supply.

Operating current less than 4mA.

Low power CMOS design.

Input frequency range: 13MHz to 30MHz for 2.5V

: 13MHz to 30MHz for 3.3V

Generates a 1X low EMI spread spectrum clock of

the input frequency.

Frequency deviation: ±1% @ 24MHz

Available in 6-pin TSOT-23, 8-pin SOIC and 8-pin

TSSOP packages.

Product Description

The ASM3P2879A is a versatile spread spectrum

frequency modulator designed specifically for a wide

range of clock frequencies. The ASM3P2879A reduces

electromagnetic interference (EMI) at the clock source,

allowing system wide reduction of EMI of

all clock

dependent signals. The ASM3P2879A allows significant

system cost savings by reducing the number of circuit

board layers ferrite beads, shielding that are traditionally

required to pass EMI regulations.

The ASM3P2879A uses the most efficient and optimized

modulation profile approved by the FCC and is

implemented by using a proprietary all digital method.

The ASM3P2879A 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 ASM3P2879A is targeted towards all portable

devices with very low power requirements like MP3

players, Notebooks and digital still cameras.

Key Specifications

Description

Specification

Supply voltages

VDD = 2.5V / 3.3V

Cycle-to-Cycle Jitter

200pS (Max)

Output Duty Cycle

45/55%

Modulation Rate Equation

Frequency Deviation

±1% @ 24MHz

Block Diagram

VSS

VDD

XIN

Frequency

Divider

Feedback

Divider

Modulation

Phase

Detector

Loop

Filter

VCO

Output

Divider

PLL

Crystal

Oscillator

XOUT

ModOUT

REFOUT