P2681A ALSC | Alldatasheet
Document overview
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Technical content
Features
FCC approved method of EMI attenuation Provides up to 15 dB of EMI suppression Generates a 1 X or ½ X low EMI spread spectrum clock of the input frequency Output frequency from 6MHz to 20MHz Digital spread selections Spreading ranges from +/-0.4% to +/-5.0% Ultra low cycle-to-cycle jitter Zero-cycle slip 3.3V and 5.0V operating voltage range 10 mA output drives TTL or CMOS compatible outputs Ultra-low power CMOS design Available in 8 pin SOIC and TSSOP Product Description The P2681A is a versatile spread spectrum frequency modulator designed specifically for digital camera and other digital video and imaging applications. The P2681A reduces electromagnetic interference (EMI) at the clock source, which provides system wide reduction of EMI of all clock dependent signals. The P2681A allows significant system cost savings by reducing the number of circuit board layers and shielding that are traditionally required to pass EMI regulations. The P2681A uses the most efficient and optimized modulation profile approved by the FCC. The P2681A 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 P2681A is targeted towards MFP, xDSL, fax modem, set-top box, USB controller, DSC, and embedded systems. Block Diagram
General Purpose EMI Reduction IC 2 of 10 Notice: The information in this document is subject to change without notice. Pin Configuration Pin Description Pin# Pin Name Type Description 1 XIN/CLKIN I Connect to crystal or clock input.
2 XOUT I Crystal output
3 DIV2 I
Digital logic input used to select normal output mode or divide-by-2 output mode. When this pin is Low, the frequency of the output clock is the same as the input clock frequency. When it is tied High, the output frequency is half the input clock frequency. This pin has an internal pull-low resistor. 4 LF I External Loop Filter for the PLL. By changing the value of the CRC circuit, the % spread can be adjusted accordingly. See Table 1.2 for detail value. 5 VSS I Ground Connection. C onnect to system ground. 6 ModOUT O Spread Spectrum Clock Output.
7 SR0 I
Digital logic input used to select Spreading Range between large or small for a given LF value (see Table 1.1 and 1.2). When SR0=0, the spreading % is smaller than SR0=1. This pin has an internal pull-up resistor. 8 VDD P Connect to +3.3V or 5.0V
General Purpose EMI Reduction IC 3 of 10 Notice: The information in this document is subject to change without notice. Table 1 - Modulation Output and Spreading Selection VDD @ 3.3V Xin 6 MHz 8 MHz 10 MHz 12 MHz 16 MHz DIV=0 ModOut 6 MHz 8 MHz 10 MHz 12 MHz 16 MHz Modulation Rate Loop filter value* TBD TBD C1=1,000 pF C2=10,000 pF R1=1K C1=1,000 pF C2=10,000 pF R1=1.5K C1=390 pF C2=3,900 pF R1=2.2K Xin 6 MHz 8 MHz 10 MHz 12 MHz 16 MHz DIV=0 ModOut 3 MHz 4 MHz 5 MHz 6 MHz 8 MHz Modulation Rate Loop filter value* TBD TBD C1=1,000 pF C2=10,000 pF R1=1K C1=1,000 pF C2=10,000 pF R1=1.5K C1=390 pF C2=3,900 pF R1=2.2K *For additional spread % selection please refer to Loop Filter Selection Table Table 2 - Loop Filter Selection Table VDD @ 3.3V Please contact Alliance Semiconductor for more information
General Purpose EMI Reduction IC 4 of 10 Notice: The information in this document is subject to change without notice. Spread Spectrum Selection The P2681A performs Zero Cycle Slip when sets at lo w % spreading. This allows no occurrence of system timing error. The optimal setting should minimize syst em EMI to the fullest without affecting system performance. The spreading is described as a percentage deviation of the center fr equency (Note: the center frequency is the frequency of the external reference input on CLKIN, Pin 1). Example: The P2681A is designed for PC peripheral applications. It is not only optimized for operation between 6MHz – 16MHz range, but its output frequency can be extended down to one ha lf of the input clock frequency using the Divide-by-Two feature. This feature extends low frequency operation to as low as 3MHz. Setting Pin 3 high (DIV2=1; Divide-by-Two mode) sets the output frequency (ModOUT) to half the frequency of the input clock (CLKIN). This is a simple way to generate a spread spectrum modulated low frequency clock when only a higher frequency signal is available. If you want the output frequency to be the same as the input, you need to set DIV2=0. The P2681A’s spread % selection is determined by the external LF value specified in Table 2. Table 1 provides a particular LF value which allows the % spreading to be selected between +/-0.75% or +/-1.30% by setting SR0 to either 0 and 1. At a specified LF value (See Table 2), SR0 pin allows the user to have the flexibility to digitally select between large or small % spreading by setting SR0=1 or SR0=0 respectively.
General Purpose EMI Reduction IC 5 of 10 Notice: The information in this document is subject to change without notice. EMC Software Simulation By using Alliance Semiconductor’s proprietary EMC simulation software – EMI-lator®, radiated system level EMI analysis can be made easier to allow a quantitative assessment on Alliance’s EMI reduction products. The simulation engine of this EMC software has already been characterized to correlate with the electrical characteristics of Alliance EMI reduction IC’s. The figur e below is an example of the simulation result. Please visit our web site at www.alsc.com for information on how to obtain a free copy and demonstration of EMI-lator®. Simulation Result from EMI-lator®
General Purpose EMI Reduction IC 6 of 10 Notice: The information in this document is subject to change without notice. Absolute Maximum Ratings Symbol Parameter Rating Unit VDD, VIN Voltage on any pin with respect to GND -0.5 to + 7.0 V TSTG Storage temperature -65 to +125 °C TA Operating temperature 0 to +70 °C Symbol Parameter Min Typ Max Unit VIL Input Low Voltage GND – 0.3 - 0.8 V VIH Input High Voltage 2.0 - V DD + 0.3 V IIL Input Low Current (internal input pull-up resistor on DIV2 and SR0) - TBD - µA IIH Input High Current (internal input pull-up resistor on DIV2 and SR0) - TBD - µA IXOL XOUT Output Low Current (@ 0.4V, VDD = 3.3V) - TBD - mA IXOH XOUT Output High Current (@ 2.5V, VDD = 3.3V) - TBD - mA VOL Output Low Voltage (VDD = 3.3V, IOL = 20 mA) - - 0.4 V VOH Output High Voltage (VDD = 3.3V, IOH = 20 mA) 2.5 - - V IDD Static Supply Current - TBD - mA ICC Dynamic Supply Current (3.3V and 10 pF loading) Xin=6MHz TBD 15 Xin=20MHz mA VDD Operating Voltage TBD 3.3 TBD V Symbol Parameter Min Typ Max Unit fIN Input Frequency when 6 - 20 MHz tLH* Output rise time (Measured at 0.8V to 2.0V) TBD ns tHL* Output fall time (Measured at 0.8V to 2.0V) TBD ns tJC Jitter (cycle to cycle) - - TBD ps tD Output duty cycle 45 50 55 % *tLH and tHL are measured into a capacitive load of 15pF
General Purpose EMI Reduction IC 7 of 10 Notice: The information in this document is subject to change without notice.
Package Information
Mechanical Package Outline 8-Pin SOIC Dimensions in inches Dimensions in millimeters Symbol Min Nor Max Min Nor Max e 0.050 BSC 1.27 BSC Note: Controlling dimensions are millimeters
General Purpose EMI Reduction IC 8 of 10 Notice: The information in this document is subject to change without notice. Mechanical Package Outline 8-Pin TSSOP Dimensions in inches Dimensions in millimeters Symbol Min Nor Max Min Nor Max A 0.047 1.10 A1 0.002 0.006 0.05 0.15 B 0.007 0.012 0.19 0.30 C 0.004 0.008 0.09 0.20 e 0.026 BSC 0.65 BSC Note: Controlling dimensions are millimeters
General Purpose EMI Reduction IC 9 of 10 Notice: The information in this document is subject to change without notice. Ordering Codes Part Number Marking Package Type Qty per reel Temperature (°C) P2681A-08ST P2681A 8-pin SOIC, tube 0 to 70 P2681A-08SR P2681A 8-pin SOIC, tape & reel 2500 0 to 70 P2681A-08TT P2681A 8-pin TSSOP, tube 0 to 70 P2681A-08TR P2681A 8-pin TSSOP, tape & reel 2500 0 to 70 Licensed under US patent Nos 5,488,627 and 5,631,920. Preliminary datasheet. Specification subject to change without notice.
General Purpose EMI Reduction IC 10 of 10 Notice: The information in this document is subject to change without notice. © Copyright 2003 Alliance Semiconductor Corporation. All rights reserved. Our three-point logo, our name and Intelliwatt are trademarks or registered trademarks of Alliance. All other brand and product names may be the trademarks of their respective companies. Alliance reserves the right to make ch anges to this document and its products at any time without notice. Alliance assumes no responsibility for any errors t hat may appear in this document. The data contained herein represents Alliance's best data and/or estimate s at the time of issuance. Alliance rese rves the right to change or correct this data at any time, without notice. If the product described herein is under development, significant changes to these specifications are possible. The information in this product data sheet is intended to be general descriptive information for potential customers and users, and is not in tended to operate as, or provide, any guarantee or warrantee to any user or customer. Alliance does not assume any responsibility or lia bility arising out of the applic ation or use of any product described herein, and disclaims any express or implied warrant ies related to the sale and/or use of Alliance products including liability or warranties related to fitness for a particular purpose, mercha ntability, or infringement of any intellec tual property rights, except as express agreed to in Alliance's Terms and Conditions of Sale (which are available from Alliance). All sales of Alliance products are made exclusively according to Alliance's Terms and Conditions of Sale. The purchase of products from Alliance does not convey a license under any pa tent rights, copyrights; mask works rights, trademarks, or any other intellectual property rights of Alli ance or third parties. Alliance does not aut horize its products for use as critical components in life-supporting systems where a malfunction or fa ilure may reasonably be expected to result in significant injury to the user, and the inclusion of Alliance products in such life-supporting systems implies that the manufacturer assumes all risk of such use and agrees to indemnify Alliance against all claims arising from such use. Alliance Semiconductor Corporation 2595, Augustine Drive, Santa Clara, CA 95054 Tel# 408-855-4900 Fax: 408-855-4999 www.alsc.com Copyright © Alliance Semiconductor All Rights Reserved Part Number: P2681A Document Version: D