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PDF SY87729L Data sheet ( Hoja de datos )
| Número de pieza | SY87729L | |
| Descripción | AnyClock FRACTIONAL N SYNTHESIZER | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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Micrel, Inc.
3.3V AnyClock™
(10MHz to 365MHz)
FRACTIONAL N SYNTHESIZER
AnyClock™
AnyClSoYc8k77™29L
SY87729L
FEATURES
■ Fractional synthesizer from 10MHz to 365MHz from a
single 27MHz reference oscillator
AnyClock™
■ Generates exactly the correct frequency for common
transport protocols with or without FEC
DESCRIPTION
■ Directly enables SY87721L to lock onto any data rate
within its range
The SY87729L is a complete rate independent frequency
■ Exceeds BellCore and ITU jitter generation
specifications
■ Programmable via MicroWire™ interface
■ Available in 32-Pin EPAD-TQFP package
synthesizer integrated circuit. From a single reference
source, this device generates a differential PECL reference
frequency for Micrel's SY87721L 10Mbps to 2.7Gbps
combined CDR and CMU.
The SY87729L generates an exactly correct reference
frequency for common data transport protocols. This is
especially important in transponder applications, where a
APPLICATIONS
standards compliant protocol data unit must be generated
downstream, even in the absence of any signal from the
■ Metro access system
■ Transponders
associated upstream interface.
In addition, SY87729L will generate exactly correct
reference frequencies for common data transport protocols
■ Multiplexers: access, add drop mux
augmented by forward error correction codes.
■ SONET/SDH/ATM-based transmission systems,
For proprietary applications, the SY87729L generates
modules and test equipment
reference frequencies guaranteed to enable the SY87721L
■ Broadband cross-connects
CDRwww.DataSheet4U.com to lock to any possible baud rate in its range.
SY87729L accepts configuration via a MicroWire™ interface.
■ Fiber optic test equipment
Data sheets and support documentation can be found on
■ Protocols supported:
Micrel’s web site at: www.micrel.com.
OC-1, OC-3, OC-12, OC-48, ATM, Gigabit Ethernet,
Fast Ethernet, Fibre Channel, 2X Fibre Channel,
1394, InfiniBand, proprietary optical transport
AnyClock is a trademarks of Micrel, Inc.
AnyRate are registered trademarks of Micrel, Inc.
MicroWire is a trademark of National Semiconductor.
M9999-040406
[email protected] or (408) 955-1690
1
Rev.: E Amendment: /0
Issue Date: April 2006
1 page  
Micrel, Inc.
AnyClock™
SY87729L
DESCRIPTION
General
The SY87729L AnyClock™ Fractional-N Synthesizer is
used in serial data streaming applications, where the
incoming data rate on a channel may vary, or where the
incoming data rate on a channel is unknown ahead of time.
In these situations, a valid output stream must still be
generated even in the absence of any edges on the
corresponding input stream. Until now, designers had to
resort to sub-optimal solutions such as providing multiple
reference oscillators. Beyond the potential noise and EMI
issues, the designer has no way to future proof his circuit,
as it would prove near impossible to pre-provision all the
reference frequencies that might be needed after
deployment, yet are unknown at this time.
The SY87729L solves this problem by generating exact
frequencies for common data streaming protocols, all from
one 27MHz reference. If any of these protocols include
overhead due to use of common digital wrappers, the
SY87729L still generates the exact frequency required,
including the overhead.
Besides generating reference rates for common protocols
directly, The SY87729L also generate reference frequencies
for Micrel’s SY87721L CDR/CMU, such that it will reliably
recover data at any rate between 28Mbps and 2,700Mbps
without any gaps.
A simple 3-wire MicroWire™ bit-serial interface loads a
configuration that describes the desired output reference
frequency. All common microcontrollers support this
MicroWire™ interface. Those microcontrollers that don’t
support this interface in hardware can easily emulate the
interface in firmware.
The large set of possible frequencies that the SY87729L
generates, are divided into three classes. First, the sets of
frequencies that match a particular data streaming protocol
are in the “protocol” category. Second, the set of frequencies
that are guaranteed to be near enough to any arbitrary data
rate such that the SY87721L will lock are in the “picket
fence” category. Third, the set of frequencies that do not fit
into either of the first two categories is in the third category,
The SY87729L generates these important reference
frequencies through two tandem PLL circuits. The first PLL
uses a modified fractional-N approach to generate a rational
ratio frequency. This PLL is capable of generating all protocol
data rates, except for those that include FEC or digital
wrapper overhead. A second, more traditional P/Q
synthesizer optionally adjusts the output frequency of the
first, fractional-N synthesizer, to accommodate these FEC
or digital wrapper data rates.
The bit serial interface conveys 32 bits of configuration
data from a microcontroller to SY87729L. This simple
interface consists of an active high chip select, a serial
clock (2MHz or less) and a serial data input. Each clock
cycle one bit of configuration data transfers to SY87729L.
Circuit Description
The heart of SY87729L is its fractional-N synthesizer, as
shown in Figure 1.
Input
Reference
Frequency
(fREF)
Loop Filter
Phase-
Frequency
Detector/
Charge
Pump
VCO
÷P
Mux
÷P-1
Output
Frequency
(fFNOUT)
Control
Figure 1. Fractional-N Synthesizer Architecture
The two dividers in the feedback path always differ by
one count. That is, if one divider is set to divide by P = 5,
then the other divider divides by P-1 = 4 . The mux chooses
between the two based on the control circuit.
The idea behind the fractional-N approach is that every
input reference edge is used. Only those output edges that
are nearest to an input edge get fed back to the phase-
frequency comparator. In addition, the nearest output edges
are chosen in such a way that the net offset, over a number
of edges, zeroes out. It is the control circuit’s job to drive
the mux such that only the “correct” edges get fed back.
In the above fractional-N circuit, if the output frequency
should be, for example, 5 times the input frequency, then P
is set to 5, and the control circuit sets the mux to only feed
back the output of the P divider.
If the output frequency should be, for example, 4 1/2 times
the input frequency, then the control circuit alternates evenly
between the P and the P-1 divider output. For every two
input edges (one to compare against P, and another to
compare against P-1), you will get 5 + 4 output edges,
yielding an output frequency 9/2 the input frequency.
Whereas P sets the integer part of the multiplication factor
from input to output frequency, the control circuit determines
the fractional part. By mixing the output of the P and P-1
dividers correctly, the control circuit can fashion any output
frequency from P-1 times the input to P times the input, as
long as that ratio can be expressed as a ratio of integers.
M9999-040406
[email protected] or (408) 955-1690
5
5 Page 
Micrel, Inc.
ABSOLUTE MAXIMUM RATINGS(1)
Symbol
VCC
VIN
IOUT
Tstore
TA
Parameter
Power Supply Voltage
Input Voltage
ECL Output Current
—Continuous
—Surge
Storage Temperature Range
Operating Temperature Range
Rating
–0.5 to +5.0
–0.5 to VCC
50
100
–65 to +150
–40 to +85
AnyClock™
SY87729L
Unit
V
V
mA
°C
°C
DC ELECTRICAL CHARACTERISTICS
VCC = VCCO = VCCA = 3.3V ±5%; GND = GNDA = 0V; TA = –40°C to +85°C
Symbol
Parameter
Min.
Typ.
Max.
VCC Power Supply Voltage 3.15 3.3 3.45
ICC Power Supply Current — 205 275
Unit
V
mA
Condition
No output load
PECL DC ELECTRICAL CHARACTERISTICS
VCC = VCCO = VCCA = 3.3V ±5%; GND = GNDA = 0V; TA = –40°C to +85°C
Symbol
Parameter
Min.
Typ.
Max.
VIH Input HIGH Voltage
VCC – 1.165 — VCC – 0.880
VIL Input LOW Voltage
VCC – 1.810 — VCC – 1.475
VOH Output HIGH Voltage VCC – 1.075 — VCC – 0.830
VOL Output LOW Voltage VCC – 1.860 — VCC – 1.570
IIL
Input LOW Current(2),(3)
–1.5
—
—
Unit
V
V
V
V
µA
Condition
50Ω to VCC –2V
50Ω to VCC –2V
VIN = VIL(Min)
TTL DC ELECTRICAL CHARACTERISTICS
VCC = VCCO = VCCA = 3.3V ±5%; GND = GNDA = 0V; TA = –40°C to +85°C
Symbol
Parameter
Min.
Typ.
Max.
Unit
Condition
VIH
VIL
VOH
VOL
IIH
IIL
IOS
Note 1.
Note 2.
Note 3.
Input HIGH Voltage
2.0 — — V
Input LOW Voltage
— — 0.8 V
Output HIGH Voltage
2.0 — — V
IOH = –2mA
Output LOW Voltage
— — 0.5 V
IOL = 4mA
Input HIGH Current
— — +20 µA VIN = 2.7V, VCC = Max.
—
—
+100
µA VIN = VCC, VCC = Max.
Input LOW Current
—
—
–300
µA VIN = 0.5V, VCC = Max.
Output Short Circuit Current
–100
—
–250
mA VOUT = 0V, (1 sec. Max.)
Permanent device damage may occur if absolute maximum ratings are exceeded. This is a stress rating only and functional operation is not
implied at conditions other than those detailed in the operational sections of this data sheet. Exposure to absolute maximum rating conditions
for extended periods may affect device reliability.
The REFCLK+ pin has a nominal 75kΩ pull-down resistor connected to ground.
The RECLK– pin has a nominal 75kΩ pull-down resistor connected to ground and a nominal 75kΩ pull-up resistor connected to VCC.
M9999-040406
[email protected] or (408) 955-1690
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet SY87729L.PDF ] | |
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