CYIFS782BSXC Datasheet CYIFS781BZXC, CYIFS782BSXC, CYIFS781BSXC | P1-P3

Low EMI Spectrum Spread Clock

FS781/82/84

Cypress Semiconductor Corporation • 198 Champion Court • San Jose, CA 95134-1709 • 408-943-2600

Document #: 38-07029 Rev. *F Revised January 2, 2005

Features

• Spread Spectrum clock generator (SSCG) with 1×, 2×,

and 4× outputs

• 6- to 82-MHz operating frequency range

• Modulates external clocks including crystals, crystal

oscillators, or ceramic resonators

• Programmable modulation with simple R-C external

loop filter (LF)

• Center spread modulation

• 3V-5V power supply

• TTL-/CMOS-compatible outputs

• Low short-term jitter

• Low-power Dissipation

— 3.3 VDC = 37 mW – typical

— 5.0 VDC = 115 mW – typical

• Available in 8-pin SOIC and TSSOP packages

Applications

• Desktop/notebook computers

• Printers, copiers, and MFP

• Scanners and fax

• LCD displays and monitors

• CD-ROM, VCD, and DVD

• Automotive and embedded systems

• Networking, LAN/WAN

• Digital cameras and camcorders

•Modems

Benefits

• Programmable EMI reduction

• Fast time to market

• Lower cost of compliance

• No degradation in rise/fall times

• Lower component and PCB layer count

Functional Description

The Cypress FS781/82/84 are Spread Spectrum clock

generator ICs (SSCG) designed for the purpose of reducing

electromagnetic interference (EMI) found in today’s

high-speed digital systems.

The FS781/82/84 SSCG clocks use a Cypress-proprietary

technology to modulate the input clock frequency, XIN, by

modulating the frequency of the digital clock. By modulating

the reference clock the measured EMI at the fundamental and

harmonic frequencies of FSOUT is greatly reduced. This

reduction in radiated energy can significantly reduce the cost

of complying with regulatory requirements without degrading

digital waveforms.

The Cypress FS781/82/84 clocks are very simple and

versatile devices to use. By programming the two range select

lines, S0 and S1, any frequency from 6- to 82-MHz operating

range can be selected. The FS781/2/4 are designed to

operate over a very wide range of input frequencies and

provides 1×, 2×, and 4× modulated clock outputs.

The FS78x devices have a simple frequency selection table

that allows operation from 6 MHz to 82 MHz in four separate

ranges. The bandwidth of the frequency spread at FSOUT is

determined by the values of the loop filter components. The

modulation rate is determined internally by the input frequency

and the selected input frequency range.

The Bandwidth of these products can be programmed from as

little as 1.0% up to as much as 4.0% by selecting the proper

loop filter value. Refer to the Loop Filter Selection chart in

Table 2 and Table 3 for the recommended values. Due to a

wide range of application requirements, an external loop filter

(LF) is used on the FS78x products. The user can select the

exact amount of frequency modulation suitable for the appli-

cation. Using a fixed internal loop filter would severely limit

the use of a wide range of modulation bandwidths (Spread %)

to a few discrete values. Refer to FS791/2/4 products for appli-

cations requiring 80- to 140-MHz frequency range.

[+] Feedback

FS781/82/84

Document #: 38-07029 Rev. *F Page 2 of 12

Output Frequency Selection

Loop Filter Selection Chart

The following table provides a list of recommended loop filter

values for the FS781/82/84. The FS78X is divided into four

ranges and operated at both 3.3V and 5.5 VDC. The loop filter

at the right is representative of the loop filter components in

Table 2.

Pin Description

Pin Name I/O Type Description

1/2 (SOIC)

3/4 (TSSOP)

OUT

I/O Analog Pins form an on-chip reference oscillator when connected to terminals

of an external parallel resonant crystal. X

may be connected to

TTL/CMOS external clock source. If X

is connected to an external clock

other than crystal, leave X

OUT

(pin 2) unconnected.

7/3 (SOIC)

1/5 (TSSOP)

S0 / S1 I CMOS/TTL Digital control inputs to select input frequency range and output

frequency scaling. Refer to Table 2 and Table 3 for selection. S0 has internal

pull-down. S1 has internal pull-up.

4 (SOIC)

6 (TSSOP)

LF I Analog Loop Filter. Single ended three-state output of the phase detector. A two-pole

passive loop filter is connected to LF.

6 (SOIC)

8 (TSSOP)

FSOUT O CMOS/TTL Modulated Clock Frequency Output. The center frequency is the same as

the input reference frequency for FS781. Input frequency is multiplied by 2×

and 4× for FS782 and FS784, respectively.

8 (SOIC)

2 (TSSOP)

P Power Positive Power Supply.

5 (SOIC)

7 (TSSOP)

P Power Power Supply Ground.

Table 1. FSOUT SSCG (Modulated Output Clock) Product Selection

Product Number FSOUT Frequency Scaling Description

FS781 1× 1× modulated frequency of input clock

FS782 2× 2× modulated frequency of input clock

FS784 4× 4× modulated frequency of input clock

Block Diagram

Pin Configuration

Phase

Detector

VCO

1(3)

2(4)

Xin

Xout

10 pF.

Reference

Divider

8 pF

250 K

VCO / N

Modulation

Control

Input Control Logic

Output

Divider

and

Mux

Power Contol

Logic

3(5)

7(1)

8(2)

5(7)

4(6)

VDD

S0S1

FSOUT

Loop Filter

VSS

6(8)

VSS

VDD

(TSSOP Pin #)

Xin

Xout

VDD

FSOUT

VSS

FS78x

8 Pin SOIC Package

VDD

Xin

Xout

FSOUT

VSS

FS78x

8 Pin TSSOP Package

LF (pin 4)

[+] Feedback

FS781/82/84

Document #: 38-07029 Rev. *F Page 3 of 12

Table 2. FS781/82/84 Recommended Loop Filter Values C7 (pF) @ +3.3 VDC ±5% (R6 = 3.3K)

[1, 2, 3, 4]

Input MHz S1 S0 BW = 1.0%

[3]

BW = 1.5%

[3]

BW = 2.0%

[3]

BW = 2.5%

[3]

BW = 3.0%

[3]

BW = 3.5%

[3]

BW = 4.0%

[3]

6 0 0 10,000/1000 1550 910 780 700 640 560

8 0 0 10,000/330 990 820 640 520 450 400

10 0 0 1040 680 460 360 300 240 210

12 0 0 830 420 300 220 200 190 170

14 0 0 580 230 200 160 140 100 80

16 0 1 10000 980 760 580 470 410 385

18 0 1 1200 750 580 470 415 370 300

20 0 1 1000 730 470 390 320 220 190

22 0 1 960 640 410 270 230 200 180

24 0 1 920 400 250 210 180 160 150

26 0 1 660 300 220 180 150 140 120

28 0 1 470 230 180 150 130 100 70

30 0 1 470 180 140 120 100 80 60

32 0 1 330 170 120 100 82 68 47

34 1 0 10000 860 640 520 430 380 330

36 1 0 2200 820 620 470 400 330 290

38 1 0 1500 690 520 410 340 290 240

40 1 0 960 600 420 340 280 220 160

42 1 0 940 620 380 275 230 210 180

44 1 0 950 680 400 250 210 190 170

46 1 0 900 580 270 220 190 180 165

48 1 0 790 440 260 210 180 160 140

50 1 0 660 360 250 190 170 150 140

52 1 0 470 325 220 185 155 135 120

54 1 0 470 270 200 170 140 130 100

56 1 0 445 250 185 150 120 85 47

58 1 0 430 210 165 130 100 65 33

60 1 0 295 185 150 120 100 90 82

62 1 0 270 220 150 120 100 82 68

64 1 1 1180 860 560 410 340 290 230

65 1 1 1180 850 540 400 330 280 220

66 1 1 1180 760 560 350 260 220 210

68 1 1 1180 750 500 320 260 230 210

70 1 1 1120 740 470 370 300 240 170

72 1 1 1160 780 470 300 250 220 190

74 1 1 1110 770 470 280 230 210 190

76 1 1 1000 720 440 240 210 190 170

78 1 1 910 670 270 210 190 170 160

80 1 1 900 620 260 210 190 170 156

82 1 1 900 540 250 210 190 170 150

Notes:

1. If the value selected from the above chart is not a standard, use the next available larger value.

2. All bandwidths indicated above are total peak-to-peak spread. 1% = +0.5% to –0.5%. 4% = +2.0% to –2.0%.

3. If C8 is not listed in the chart for a particular bandwidth and frequency, it is not used in the loop filter.

4. Contact Cypress for LF values less than 1.0% bandwidth.

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