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W166
Spread Spectrum Frequency Timing Generator
Features
* Maximized EMI suppression using Cypress's Spread Spectrum technology * Generates a spread spectrum copy of the provided input * Selectable spreading characteristics * Integrated loop filter components * Operates with a 3.3V or 5V supply * SSON# pin enables frequency spreading * Low power CMOS design * Available in 8-pin SOIC (Small Outline Integrated Circuit) is greatly reduced. Use of this technology allows systems to pass increasingly difficult EMI testing without resorting to costly shielding or redesign. In a system, not only is EMI reduced in the various clock lines, but also in all signals which are synchronized to the clock. Therefore, the benefits of using this technology increase with the number of address and data lines in the system. The Simplified Block Diagram shows a simple implementation. Table 1. Frequency Spread Selection W166 FS1 0 0 The W166 incorporates the latest advances in PLL spread spectrum frequency synthesizer techniques. By frequency modulating the output with a low-frequency carrier, peak EMI 1 1 FS0 0 1 0 1 Input Frequency (MHz) 50 to 65 50 to 65 50 to 65 50 to 65 Output Frequency (MHz) fIN 0.625% fIN 1.25% fIN 2.5% fIN -3.75%
Overview
Simplified Block Diagram
3.3V or 5V
Pin Configuration
Oscillator or Reference Input
CLKIN NC GND FS1
1 2 3 4
8 7 6 5
SSON# CLKOUT FS0 VDD
W166
W166
Spread Spectrum Output (EMI suppressed)
Cypress Semiconductor Corporation
*
3901 North First Street
*
San Jose
*
CA 95134 * 408-943-2600 December 20, 1999, rev. **
W166
Pin Definitions
Pin Name CLKOUT CLKIN NC SSON# FS0:1 VDD GND Pin No. 7 1 2 8 6, 4 5 3 Pin Type O I NC I I P G Pin Description Output Modulated Frequency: Frequency modulated copy of the reference input (SSON# asserted). External Reference Frequency Input: Clock input. No Connect: This pin must be left unconnected. Spread Spectrum Control (Active LOW): Asserting this signal (active LOW) turns the internal modulation waveform on. This pin has an internal pull-down resistor. Frequency Selection Bits 0,1: These pins select the frequency spreading characteristics. Refer to Table 1. These pins have internal pull-up resistors. Power Connection: Connected to 3.3V or 5V power supply. Ground Connection: This should be connected to the common ground plane. Because the modulating frequency is typically 1000 times slower than the fundamental clock, the spread spectrum process has little impact on system performance. Frequency Selection With SSFTG In Spread Spectrum Frequency Timing Generation, EMI reduction depends on the shape, modulation percentage, and frequency of the modulating waveform. While the shape and frequency of the modulating waveform are fixed, the modulation percentage may be varied. A larger spreading percentage improves EMI reduction. However, large spread percentages may either exceed system maximum frequency ratings or lower the average frequency to a point where performance is affected. For these reasons, narrow and wide modulation selections are provided.
Functional Description
The W166 uses a Phase-Locked Loop (PLL) to frequency modulate an input clock. The result is an output clock whose frequency is slowly swept over a narrow band near the input signal. The basic circuit topology is shown in Figure 1. The input reference signal is divided by Q and fed to the phase detector. A signal from the VCO is divided by P and fed back to the phase detector also. The PLL will force the frequency of the VCO output signal to change until the divided output signal and the divided reference signal match at the phase detector input. The output frequency is then equal to the ratio of P/Q times the reference frequency. (Note: For the W166 the output frequency is equal to the input frequency.) The unique feature of the Spread Spectrum Frequency Timing Generator is that a modulating waveform is superimposed at the input to the VCO. This causes the VCO output to be slowly swept across a predetermined frequency band.
VDD
Clock Input Freq. Divider Q Phase Detector Charge Pump
Reference Input
VCO
Post Dividers
CLKOUT (EMI suppressed)
Modulating Waveform Feedback Divider P
PLL
GND
Figure 1. System Block Diagram
2
W166
Spread Spectrum Frequency Timing Generator
The device generates a clock that is frequency modulated in order to increase the bandwidth that it occupies. By increasing the bandwidth of the fundamental and its harmonics, the amplitudes of the radiated electromagnetic emissions are reduced. This effect is depicted in Figure 2. As shown in Figure 2, a harmonic of a modulated clock has a much lower amplitude than that of an unmodulated signal. The reduction in amplitude is dependent on the harmonic number and the frequency deviation or spread. The equation for the reduction is dB = 6.5 + 9*log10(P) + 9*log10(F) Where P is the percentage of deviation and F is the frequency in MHz where the reduction is measured. The output clock is modulated with a waveform depicted in Figure 3. This waveform, as discussed in "Spread Spectrum Clock Generation for the Reduction of Radiated Emissions" by Bush, Fessler, and Hardin produces the maximum reduction in the amplitude of radiated electromagnetic emissions. The deviation selected for this chip is 0.45% or 0.6% of the selected frequency. Figure 3 details the Cypress spreading pattern. Cypress does offer options with more spread and greater EMI reduction. Contact your local Sales representative for details on these devices.
E M I R e d u ctio n
S SFTG
Typical Clock
Amplitude (dB)
A m plitu de (dB )
S p re a d S p e ctru m E n a b le d
NonS p re a d Spectrum
Frequency Span (MHz)
Center Spread
Frequency Span (MHz) Down Spread
Figure 2. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
MAX.
FREQUENCY
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10%
20%
30%
40%
50%
60%
70%
80%
90%
MIN.
Figure 3. Typical Modulation Profile
3
100%
W166
Absolute Maximum Ratings
Stresses greater than those listed in this table may cause permanent damage to the device. These represent a stress rating only. Operation of the device at these or any other conditions
.
above those specified in the operating sections of this specification is not implied. Maximum conditions for extended periods may affect reliability Rating -0.5 to +7.0 -65 to +150 0 to +70 -55 to +125 0.5 Unit V C C C W
Parameter VDD, VIN TSTG TA TB PD
Description Voltage on any Pin with Respect to GND Storage Temperature Operating Temperature Ambient Temperature under Bias Power Dissipation
DC Electrical Characteristics: 0C < TA < 70C, VDD = 3.3V 5%
Parameter IDD tON VIL VIH VOL VOH IIL IIH IOL IOH CI CI RP ZOUT Description Supply Current Power Up Time Input Low Voltage Input High Voltage Output Low Voltage Output High Voltage Input Low Current Input High Current Output Low Current Output High Current Input Capacitance Input Capacitance Input Pull-Up Resistor Clock Output Impedance Note 1 Note 1 @ 0.4V, VDD = 3.3V @ 2.4V, VDD = 3.3V All pins except CLKIN CLKIN pin only 6 500 25 15 15 7 5 2.4 -20 20 2.4 0.4 First locked clock cycle after Power Good Test Condition Min Typ 18 Max 32 5 0.8 Unit mA ms V V V V A A mA mA pF pF k
Note: 1. Inputs FS1:0 have a pull-up resistor, Input SSON# has a pull-down resistor.
4
W166
DC Electrical Characteristics: 0C < TA < 70C, VDD = 5V 10%
Parameter IDD tON VIL VIH VOL VOH IIL IIH IOL IOH CI CI RP ZOUT Description Supply Current Power Up Time Input Low Voltage Input High Voltage Output Low Voltage Output High Voltage Input Low Current Input High Current Output Low Current Output High Current Input Capacitance Input Capacitance Input Pull-Up Resistor Clock Output Impedance Note 1 Note 1 @ 0.4V, VDD = 5V @ 2.4V, VDD = 5V All pins except CLKIN CLKIN pin only 500 25 24 24 7 5 2.4 -20 20 3.5 0.4 First locked clock cycle after Power Good Test Condition Min Typ 21 Max 40 5 0.8 Unit mA ms V V V V A A mA mA pF pF k
AC Electrical Characteristics: TA = 0C to +70C, VDD = 3.3V 5% or 5V10%
Symbol fIN fOUT tR tF tOD tID tJCYC Parameter Input Frequency Output Frequency Output Rise Time Output Fall Time Output Duty Cycle Input Duty Cycle Jitter, Cycle-to-Cycle Harmonic Reduction fout = 50 MHz, third harmonic measured, reference board, 15-pF load 8 Test Condition Input Clock Spread Off 15-pF load, 0.8V-2.4V 15-pF load, 2.4V-0.8V 15-pF load, test at VDD/2 40 40 250 Min 50 50 2 2 Typ Max 65 65 5 5 60 60 300 Unit MHz MHz ns ns % % ps dB
5
W166
Application Information
Recommended Circuit Configuration For optimum performance in system applications the power supply decoupling scheme shown in Figure 4 should be used. VDD decoupling is important to both reduce phase jitter and EMI radiation. The 0.1-F decoupling capacitor should be placed as close to the VDD pin as possible, otherwise the increased trace inductance will negate its decoupling capability. The 10-F decoupling capacitor shown should be a tantalum type. For further EMI protection, the VDD connection can be made via a ferrite bead, as shown. Recommended Board Layout Figure 5 shows a recommended a 2-layer board layout.
Reference Input NC GND
1 W166 2 3 4
8 7 6 5
R1 Clock Output VDD
C1 0.1 F
3.3 or 5V System Supply
FB
C2 10 F Tantalum
Figure 4. Recommended Circuit Configuration
C1 = C2 =
High frequency supply decoupling capacitor (0.1 F recommended). Common supply low frequency decoupling capacitor (10-F tantalum recommended). Match value to line impedance Ferrite Bead
Via To GND Plane
R1 = FB =
=
G
Reference Input NC R1
Clock Output
G
C1 G C2 G
Power Supply Input (3.3V or 5V)
FB
Figure 5. Recommended Board Layout (2-Layer Board)
Ordering Information
Ordering Code W166 Document: #38-00878 Package Name G Package Type 8-pin Plastic SOIC (150-mil)
6
W166
Package Diagram
8-Pin Small Outlined Integrated Circuit (SOIC, 150-mil)
(c) Cypress Semiconductor Corporation, 1999. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress Semiconductor product. Nor does it convey or imply any license under patent or other rights. Cypress Semiconductor does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress Semiconductor products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress Semiconductor against all charges.

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