Rainbow Electronics DS1080L - Manual (Page 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
IN
/ 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%
f 0
-1.0%
-1.5%
DITHER CYCLE RATE = f DITHER = f IN / 1024
f SSO
t
Figure 1. Spread-Spectrum Frequency Modulation