DS1080CL Datasheet, PDF (6/8 Pages) Maxim Integrated Products – Spread-Spectrum Crystal Multiplier

Spread-Spectrum Crystal Multiplier
Detailed Description
The DS1080CL is a crystal multiplier with center
spread-spectrum capability. An 8MHz to 16MHz crystal
is connected to the X1 and X2 pins. Alternately, an
8MHz to 16MHz clock can be applied to X1 in place of
the crystal. In such applications, X2 would be left open
circuit. Using the CMSEL input, the user selects
whether the attached crystal or input clock is multiplied
by 1, 2, or 4. The DS1080CL can generate spread-
spectrum clocks from 8MHz to 64MHz.
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 high
impedance. If the PDN pin is open, the SSO output is
active but the spread-spectrum dithering is disabled.
The spread-spectrum dither rate is fixed at f_IN/512 to
keep the dither rate above the audio frequency range.
On power-up, the output clock (SSO) remains high
impedance until the PLL reaches a stable frequency
(f_SSO) and dither (f_DITHER). A power cycle is needed
for the PLL whenever there is a change in input fre-
quency, CMSEL, or SMSEL.
+1.5%
+1.0%
+0.5%
f_O
-0.5%
-1.0%
-1.5%
DITHER CYCLE RATE = f_DITHER = f_IN/512
t
Figure 1. Spread-Spectrum Frequency Modulation
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