Datasheet

MAX31180
Spread-Spectrum Crystal Multiplier
6Maxim Integrated
Block Diagram
Detailed Description
The MAX31180 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 MAX31180 is capable of generating spread-
spectrum clocks from 16MHz to 134MHz.
The PLL can dither the output clock about its center
frequency 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 three-stat-
ed. 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
/992 to keep the dither
rate above the audio frequency range. On power-up, the
output clock (SSO) remains three-stated until the PLL
reaches a stable frequency (f
SSO
) and dither (f
DITHER
).
Applications Information
Crystal Selection
The MAX31180 requires a parallel resonating crystal
operating in the fundamental mode, with an ESR of less
than 90Ω. The crystal should be placed very close to the
device to minimize excessive loading due to parasitic
capacitances.
Oscillator Input
When driving the MAX31180 using an external oscillator
clock, consider the input (X1) to be high impedance.
CRYSTAL
OSCILLATOR
1x/2x/4x CLOCK MULTIPLYING
PLL WITH SPREAD SPECTRUM
CONFIGURATION DECODE
AND CONTROL
V
CC
V
CC
GND
NOTE: SEE INFORMATION ABOUT C
L1
AND C
L2
IN THE APPLICATIONS INFORMATION SECTION AT THE END OF THE DATA SHEET.
PDN
SSO
CMSEL
SMSEL
X1
X2
16MHz
TO
33.4MHz
f
SSO
= 16MHz
TO
134MHz
C
L1
C
L2
f
IN
f
SSO
MAX31180