September 2004
rev 1.0
Peak Reducing EMI Solution
Features
•
Generates an EMI optimized clocking
signal at the output.
•
Selectable output frequency range.
•
Single 1.25% or 2.4% down spread
output.
•
Integrated loop filter components.
•
Operates with a 3.3V supply.
•
Low-power CMOS design.
•
Available in 8-pin SOIC and 8-pin
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
Simplified Block Diagram
ASM3P2180A
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
Supply voltages
Frequency
range
FS1=0
FS1=1
Specification
V
DD
= 3.3V ± 5%
6 MHz
≤
Fin
≤10
MHz
18 MHz
≤
Fin
≤
30 MHz
325 pS (max)
-1.25% or –2.4%
45/55% (worst case)
5ns (maximum)
Cycle-to-cycle jitter
Selectable spread percentage
Output duty cycle
Output rise and fall time
3.3V
X1
ASM3P2180A
X2
Spread spectrum output
(EMI suppressed)
Alliance Semiconductor
2595, Augustine Drive
•
Santa Clara
•
CA 95054
•
Tel 408 855 4900
•
Fax 408 855 4999
•
www.alsc.com
Notice: The information in this document is subject to change without notice.
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
