Alliance Semiconductor

2575 Augustine Drive

• Santa Clara CA • Tel: 408-855-4900 • Fax: 408-855-4999 • www.alsc.com

rev 0.7

December 2004

ASM3P2853A

Peak EMI Reducing Solution

Features

Generates an EMI optimized clock signal at

output.

Input frequency: 25 MHz.

Frequency outputs:

o

USB Clock (48 MHz unmodulated)

o

50 MHz (modulated), ±1% centre spread

Modulation rate: 39 KHz.

Spread Spectrum ON/OFF control

Supply voltage range 2.5V ± 5%.

Available in 8-pin SOIC package.

Commercial Temperature range.

Product Description

The ASM3P2853A is a versatile spread spectrum

frequency

modulator.

The

ASM3P2853A

reduces

electromagnetic interference (EMI) at the clock source.

The ASM3P2853A allows significant system cost savings

by reducing the number of circuit board layers and

shielding that are required to pass EMI regulations. The

ASM3P2853A modulates the output of PLL in order to

spread the bandwidth of a synthesized clock, thereby

decreasing 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 clock generators. Lowering EMI by increasing a

signal’s bandwidth is called spread spectrum clock

generation.

Applications

ASM3P2853A is targeted towards EMI management for

high speed digital applications such as PC peripheral

devices, consumer electronics and embedded controller

systems.

Block Diagram

Crystal

Oscillator

50 MHz

Modulated

XIN

XOUT

USB Clock

(48 MHz

Unmodulated)

PLL1

PLL2

PWDNB

SSONB