ASM3P18S19B Datasheet, PDF (1/7 Pages) Alliance Semiconductor Corporation – Notebook LCD Panel EMI Reduction IC

August 2005
ASM3P18S19B
rev 2.1
Notebook LCD Panel EMI Reduction IC
Features
ƒ FCC approved method of EMI attenuation.
ƒ Provides up to 15dB EMI reduction.
ƒ Generates a low EMI Spread Spectrum clock and a
non-spread reference clock of the input frequency.
ƒ Optimized for Frequency range from 20 to 40MHz.
ƒ Internal loop filter minimizes external components and
board space.
ƒ Low Inherent Cycle-to-Cycle jitter.
ƒ Two spread % selections: -1.25% to -1.75%.
ƒ 3.3V Operating Voltage.
ƒ Low power CMOS design.
ƒ Supports notebook VGA and other LCD timing
controller applications.
ƒ Power Down function for mobile application.
ƒ Available in Commercial temperature range.
ƒ Available in 8-pin SOIC and TSSOP Packages.
ƒ RoHS Compliant
Product Description
The ASM3P18S19B 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 ASM3P18S19B reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of down stream
clock and data dependent signals. The ASM3P18S19B
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 ASM3P18S19B 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 ASM3P18S19B uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented in a proprietary all digital method.
Applications
The ASM3P18S19B 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
PD# SRS
VDD
XIN/CLKIN
XOUT
Crystal
Oscillator
REF
Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
PLL
VCO
Output
Divider
ModOUT
VSS
Alliance Semiconductor
2575 Augustine Drive • Santa Clara, CA • Tel: [phone] • Fax: [phone] • www.alsc.com
Notice: The information in this document is subject to change without notice.