July 2005
rev 1.5
P2781/82/84
General Purpose EMI Reduction IC
Features
other digital video and imaging applications. The P278xA
reduces electromagnetic interference (EMI) at the clock
source, which provides system wide reduction of EMI of
all clock dependent signals. The P278xA allows
significant system cost savings by reducing the number of
circuit board layers and shielding that are traditionally
required to pass EMI regulations.
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Provides up to 15dB of EMI suppression
FCC approved method of EMI attenuation
Generates a 1X, 2X, and 4X low EMI spread
spectrum clock of the input frequency
Input frequency range from 3 to 78MHz
External loop filter for spread % adjustment
Spreading ranges from ±0.25% to ±5.0%
Ultra low cycle-to-cycle jitter
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The P278xA uses the most efficient and optimized
modulation profile approved by the FCC. The P278xA
modulates the output of a single PLL in order to “spread”
Zero-cycle slip
the bandwidth of
a synthesized clock and, more
3.3V operating voltage range
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.
10 mA output drives
TTL or CMOS compatible outputs
Ultra-low power CMOS design
P278XA is available in 8 pin SOIC and TSSOP
Packages
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Available for industrial and automotive
temperature ranges.
Applications
Product Description
The P278xA is a versatile spread spectrum frequency
modulator designed specifically for digital camera and
The P278xA is targeted towards MFP, xDSL, fax modem,
set-top box, USB controller, DSC, and embedded systems.
LF
VDD
FS1
FS0
Block Diagram
PLL
Modulation
XIN /CLKIN
Frequency
Crystal
Divider
Output
Divider
Oscillator
XOUT
Phase
Detector
VCO
Feedback
Divider
ModOUT
VSS
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.
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
