P2781 Datasheet, PDF (1/8 Pages) Alliance Semiconductor Corporation – General Purpose EMI Reduction IC

P2781/82/84
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
• Ultra-low power CMOS design
• P278xA is available in an 8 pin SOIC Package
Product Description
The P278xA is a versatile spread spectrum frequency
modulator designed specifically for digital camera and 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 “spread”
the bandwidth of a synthesized clock and, more
importantly, decreases the peak amplitudes of its
harmonics. This result 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.
Applications
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
©2010 SCILLC. All rights reserved.
JANUARY 2010 – Rev. 2
VSS
Publication Order Number:
P2781/82/84