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I2779A

Low-Cost Notebook EMI Reduction IC

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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 frequency range External loop filter for spread percentage adjustment 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

Modulation Crystal oscillator Frequency divider Feedback divider Phase detector Loop filter

PLL

VCO

Output divider

REF

ModOUT

VSS

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

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 XOUT PD LF 1 2 3 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.

P2779A
®

Pin Description
Pin # 1 2 3 4 Name XIN/CLKIN XOUT PD LF Type I I I I Connect to crystal or clock input. Crystal output. Power-down control pin. Pull low to enable power-down mode. This pin has an internal pull-up resistor.1 External


























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