November 2005

P1819

rev 1.7

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.

Notebook LCD Panel EMI Reduction IC

Features

FCC approved method of EMI attenuation.

Provides up to 15dB EMI reduction.

Generates a low EMI Spread Spectrum clock and a

non-spread reference clock of the input frequency.

Optimized for Frequency range from 20 to 40MHz.

Internal loop filter minimizes external components

and board space.

Selectable spread options: Down and Center.

Low Inherent Cycle-to-Cycle jitter.

Eight spread % selections:

±0.625% to –3.5%.

3.3V

± 0.3V Operating Voltage range.

Low power CMOS design.

Supports notebook VGA and other LCD timing

controller applications.

Power Down function for mobile application.

Available in Commercial temperature range.

Available in 8-pin SOIC and TSSOP Packages.

Product Description

The P1819 is a Versatile Spread Spectrum Frequency

Modulator designed specifically for input clock frequencies

from 20 to 40MHz. (Refer Input Frequency and Modulation

Rate

Table).

The

P1819

reduces

electromagnetic

interference (EMI) at the clock source, allowing system

wide reduction of EMI of down stream clock and data

dependent signals. The P1819 allows significant system

cost savings by reducing the number of circuit board layers

ferrite beads, shielding and other passive components that

are traditionally required to pass EMI regulations.

The P1819 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’.

The P1819 uses the most efficient and optimized

modulation profile approved by the FCC and is

implemented in a proprietary all digital method.

Applications

The P1819 is targeted towards EMI management for

memory and LVDS interfaces in mobile graphic chipsets

and high-speed digital applications such as PC peripheral

devices, consumer electronics, and embedded controller

systems.

Block Diagram

VSS

VDD

ModOUT

XIN/CLKIN

Frequenc

y

Feedback

Divider

Modulation

Phase

Detector

Loop

Filter

VCO

Output

Divider

PLL

SRS

D_C/NC PD#

Crystal

Oscillator

XOUT

REF