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P2781 Datasheet, PDF (1/11 Pages) Alliance Semiconductor Corporation – General Purpose EMI Reduction IC | |||
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July 2005
P2781/82/84
rev 1.5
General Purpose EMI Reduction IC
Features
 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
 Zero-cycle slip
 3.3V operating voltage range
 10 mA output drives
 TTL or CMOS compatible outputs
 Ultra-low power CMOS design
 P278XA is available in 8 pin SOIC and TSSOP
Packages
 Available for industrial and automotive
temperature ranges.
Product Description
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.
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 âspreadâ
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 signalâs bandwidth is called spread
spectrum clock generation.
Applications
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.
Block Diagram
FS0 FS1 LF VDD
XIN /CLKIN
XOUT
Crystal
Oscillator
Frequency
Divider
Feedback
Divider
PLL
Modulation
Phase
Detector
VCO
Output
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.
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