Clock Generator with Dual PLLs,
Spread Spectrum, and Margining
AD9577
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
REFSEL
Fully integrated dual PLL/VCO cores
1 integer-N and 1 fractional-N PLL
XT1
OSC
XT2
XTAL
CMOS
Continuous frequency coverage from 11.2 MHz to 200 MHz
Most frequencies from 200 MHz to 637.5 MHz available
PLL1 phase jitter (12 kHz to 20 MHz): 460 fs rms typical
PLL2 phase jitter (12 kHz to 20 MHz)
REFOUT
REFCLK
DIVIDE
1 OR 2
LDO
PLL1
Integer-N mode: 470 fs rms typical
Fractional-N mode: 660 fs rms typical
VCO
LVPECL/LVDS
OR 2 × CMOS
2.15GHz
TO
Input crystal or reference clock frequency
Optional reference frequency divide-by-2
I2C programmable output frequencies
Up to 4 LVDS/LVPECL or up to 8 LVCMOS output clocks
1 CMOS buffered reference clock output
Spread spectrum: downspread [0, −0.5]%
2 pin-controlled frequency maps: margining
Integrated loop filters
2.55GHz
LVPECL/LVDS
OR 2 × CMOS
FEEDBACK
DIVIDER
LDO
PLL2
VCO
2.15GHz
TO
LVPECL/LVDS
OR 2 × CMOS
2.55GHz
Space saving, 6 mm × 6 mm, 40-lead LFCSP package
1.02 W power dissipation (LVDS operation)
1.235 W power dissipation (LVPECL operation)
3.3 V operation
LVPECL/LVDS
OR 2 × CMOS
FEEDBACK
DIVIDER
SCL
SDA
2
I C
CONTROL
MARGIN
APPLICATIONS
AD9577
SSCG
SPREAD SPECTRUM,
SDM
MAX_BW
Low jitter, low phase noise multioutput clock generator for
data communications applications including Ethernet,
Fibre Channel, SONET, SDH, PCI-e, SATA, PTN, OTN,
ADC/DAC, and digital video
Figure 1.
feedback divider, and two independently programmable output
dividers. By connecting an external crystal or applying a reference
clock to the REFCLK pin, frequencies of up to 637.5 MHz can
be synchronized to the input reference. Each output divider and
feedback divider ratio is I2C programmed for the required
output rates.
Spread spectrum clocking
GENERAL DESCRIPTION
The AD9577 provides a multioutput clock generator function,
along with two on-chip phase-locked loop cores, PLL1 and PLL2,
optimized for network clocking applications. The PLL designs
are based on the Analog Devices, Inc., proven portfolio of high
performance, low jitter frequency synthesizers to maximize
network performance. The PLLs have I2C programmable output
frequencies and formats. The fractional-N PLL can support
spread spectrum clocking for reduced EMI radiated peak power.
Both PLLs can support frequency margining. Other applications
with demanding phase noise and jitter requirements can benefit
from this part.
A second fractional-N PLL (PLL2) with a programmable modulus
allows VCO frequencies that are fractional multiples of the
reference frequency to be synthesized. Each output divider
and feedback divider ratio can be programmed for the required
output rates, up to 637.5 MHz. This fractional-N PLL can also
operate in integer-N mode for the lowest jitter.
Up to four differential output clock signals can be configured
as either LVPECL or LVDS signaling formats. Alternatively,
the outputs can be configured for up to eight CMOS outputs.
Combinations of these formats are supported. No external loop
filter components are required, thus conserving valuable design
time and board space. The AD9577 is available in a 40-lead, 6 mm ×
6 mm LFCSP package and can operate from a single 3.3 V supply.
The operating temperature range is −40°C to +85°C.
The first integer-N PLL section (PLL1) consists of a low noise phase
frequency detector (PFD), a precision charge pump (CP), a low
phase noise voltage controlled oscillator (VCO), a programmable
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2011 Analog Devices, Inc. All rights reserved.
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