Maker : ETC
Part No. : I2779A

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Product Information

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 loop filter for the PLL. By changing the value of the CRC circuit, the percentage spread can be adjusted accordingly. (See Loop Filter Selection Table for detail value.) Ground connection. Connect to system ground. Spread Spectrum clock output. Provides a reference clock output of the input frequency. Connect to +3.3 V. Description 5 6 7 8 VSS ModOUT REF VDD P O O P 1. Connect to VDD if not used. Loop Filter Selection Table VDD 3.3 V R1 Pin 4 LF C2 C1 BW = ± 0.50% Input FS1 FS0 (MHz) 20 21 - 22 23 - 24 25 - 26 27 - 28 29 - 30 31 - 32 33 - 34 35 - 36 37 - 38 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 BW = ± 0.75% C1 270 270 270 270 270 270 270 270 270 270 BW = ± 1.00% C1 270 270 270 270 270 270 270 270 270 270 BW = ± 1.25% C1 560 560 680 470 330 330 680 390 270 270 C1 (pF) 270 270 270 270 270 270 270 270 270 270 C2 (pF) 100,000 100,000 100,000 100,000 100,000 100,000 100,000 100,000 100,000 100,000 R1 330 390 510 560 620 750 820 910 1,000 1,200 (ohms) (pF) C2 (pF) 100,000 100,000 100,000 100,000 100,000 100,000 100,000 100,000 100,000 100,000 R1 560 620 750 820 1,000 1,100 1,200 1,300 1,500 1,600 (ohms) (pF) C2 (pF) 100,000 10,000 12,000 6,800 3,900 12,000 10,000 5,600 3,300 R1 750 1,000 1,200 1,200 1,200 2,200 2,200 2,200 2,200 (ohms) (pF) C2 (pF) 100,000 100,000 6,800 4,700 3,300 3,300 6,800 3,900 2,700 2,700 R1 (ohms) 910 1,100 1,200 1,200 1,200 1,500 2,200 2,200 2,200 2,700 100,000 866(1%) Plese contact factory for loop filter values if desired spr...

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