Rainbow-electronics DS1080L Manual de usuario descargar pdf (Pagina 6)

DS1080L

Spread-Spectrum Crystal Multiplier

6 _____________________________________________________________________

Detailed Description

The DS1080L is a crystal multiplier with center spread-

spectrum capability. A 16MHz to 33.4MHz crystal is

connected to the X1 and X2 pins. Alternately, a 16MHz

to 33.4MHz clock can be applied to X1 in place of the

crystal. In such applications, X2 would be left open cir-

cuit. Using the CMSEL input, the user selects whether

the attached crystal or input clock is multiplied by 1, 2,

or 4. The DS1080L is capable of generating spread-

spectrum clocks from 16MHz to 134MHz.

The PLL can dither the output clock about its center fre-

quency at a user-selectable magnitude. Using the

SMSEL input, the user selects the dither magnitude.

The PDN input can be used to place the device into a

low-power standby mode where the SSO output is tri-

stated. If the PDN pin is floated, the SSO output is

active but the spread-spectrum dithering is disabled.

The spread-spectrum dither rate is fixed at f

/ 1024 to

keep the dither rate above the audio frequency range.

On power-up, the output clock (SSO) remains tri-stated

until the PLL reaches a stable frequency (f

SSO

) and

dither (f

DITHER

+1.5%

+1.0%

+0.5%

-0.5%

-1.0%

-1.5%

DITHER CYCLE RATE = f

DITHER

= f

/ 1024

SSO

Figure 1. Spread-Spectrum Frequency Modulation

1 2 3 4 5 6 7 8

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Rainbow-electronics DS1080L Manual de usuario Pagina 6