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I2779A Datasheet

Low-Cost Notebook EMI Reduction IC

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I2779A pdf
Production
February 2003
® P2779A
Low-Cost Notebook EMI Reduction IC
Features
• Provides up to 15 dB of EMI suppression
• FCC approved method of EMI attenuation
• Generates a 1X low EMI spread spectrum clock of
the input frequency
• Operates between 20MHz and 38MHz input fre-
quency range
• External loop filter for spread percentage adjust-
ment
• Spreading ranges from ±0.25% to ±2.5%
• Ultra low cycle-to-cycle jitter
• Zero-cycle slip at small deviations
• 3.3 V operating voltage range
• 10 mA output drives
• TTL or CMOS compatible outputs
• Low power CMOS design
• Available in 8-pin SOIC and TSSOP
• Available for industrial temperature operating
range (-40º C to 85º C)
Block Diagram
PD LF VDD
XIN
XOUT
Crystal
oscillator
REF
Frequency
divider
Feedback
divider
Modulation
Phase
detector
Loop
filter
PLL
VCO
Output
divider
ModOUT
Product Description
The P2779A is a versatile spread spectrum frequency
modulator designed specifically for mobile and digital
camera and other digital video and imaging
applications. The P2779A reduces electromagnetic
interference (EMI) at the clock source, which provides
system-wide reduction of EMI of all clock dependent
signals. The P2779A allows significant system cost
savings by reducing the number of circuit board layers
and shielding that are traditionally required to pass EMI
regulations.
The P2779A uses the most efficient and optimized
modulation profile approved by the FCC.
The P2779A 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
VSS
produced by oscillators and most frequency generators.
Lowering EMI by increasing a signal’s bandwidth is
called spread spectrum clock generation.
Applications
The P2779A is targeted toward mobile 3D graphics chip
set applications
Pin Diagram
XIN/CLKIN 1
XOUT 2
PD 3
LF 4
8 VDD
7 REF
6 ModOUT
5 VSS
Alliance Semiconductor
2575 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.
ETC
ETC



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