ASM3P2853A

Peak EMI Reducing Solution

©2010 SCILLC. All rights reserved.

Publication Order Number:

FEBRUARY 2012 – Rev. 3

ASM3P2853/D

Features

• Generates an EMI optimized clock signal at output.

• Input frequency: 25MHz.

• Frequency outputs:

o

USB Clock (48MHz unmodulated)

o

50MHz (modulated), ±1% centre spread

• Modulation rate: 39KHz.

• Spread Spectrum ON/OFF control

• Supply voltage range 2.5V ± 5%.

• Available in 8-Pin SOIC package.

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

50MHz

Modulated

XIN

XOUT

USB Clock

(48MHz

Unmodulated)

PLL1

PLL2

PWDNB

SSONB