Alliance Semiconductor

2595, Augustine Drive

• Santa Clara • CA 95054 • Tel 408 855 4900 • Fax 408 855 4999 • www.alsc.com

September 2004

ASM3P2180A

rev 1.0

Notice: The information in this document is subject to change without notice.

Peak Reducing EMI Solution

Features

signal at the output.

output.

TSSOP packages.

Product Description

The ASM3P2180A is a versatile Spread

Spectrum

frequency

modulator

designed

specifically

for

a

wide

range

of

clock

frequencies.

The

ASM3P2180A

reduces

electromagnetic interference (EMI) at the clock

source, allowing system wide reduction of EMI

of down stream clock and data dependent

signals. The ASM3P2180A allows significant

system cost savings by reducing the number of

circuit board layers and shielding that are

traditionally required to pass EMI regulations.

The ASM3P2180A modulates the output of a

single 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.

The ASM3P2180A uses the most efficient and

optimized modulation profile approved by the

FCC and is implemented by using a proprietary

all-digital method.

Applications

The ASM3P2180A is targeted towards notebook

LCD displays, other displays using an LVDS

interface, PC peripheral devices and embedded

systems.

Key Specifications

Description

Specification

Supply voltages

FS1=0

6 MHz

≤ Fin ≤10 MHz

Frequency

range

FS1=1

18 MHz

≤ Fin ≤ 30 MHz

Cycle-to-cycle jitter

325 pS (max)

Selectable spread percentage

-1.25% or –2.4%

Output duty cycle

45/55% (worst case)

Output rise and fall time

5ns (maximum)

Simplified Block Diagram

X1

X2

3.3V

Spread spectrum output

(EMI suppressed)

ASM3P2180A