ICS345
Triple PLL Field Programmable SS VersaClock Synthesizer
Description
The ICS345 field programmable clock synthesizer
generates up to nine high-quality, high-frequency clock
outputs including multiple reference clocks from a
low-frequency crystal or clock input. It is designed to
replace crystals and crystal oscillators in most
electronic systems.
Using ICS’
software to configure PLLs
and outputs, the ICS345 contains a One-Time
Programmable (OTP) ROM to allow field
programmability. Programming features include eight
selectable configuration registers, up to two sets of four
low-skew outputs, and optional Spread Spectrum
outputs.
Using Phase-Locked Loop (PLL) techniques, the
device runs from a standard fundamental mode,
inexpensive crystal, or clock. It can replace multiple
crystals and oscillators, saving board space and cost.
The ICS345 is also available in factory programmed
custom versions for high-volume applications.
VersaClock
TM
Features
•
•
•
•
•
•
•
•
•
•
•
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Packaged as 20-pin SSOP (QSOP)
Spread spectrum capability
Eight addressable registers
Replaces multiple crystals and oscillators
Output frequencies up to 200 MHz at 3.3 V
Input crystal frequency of 5 to 27 MHz
Input clock frequency of 2 to 50 MHz
Up to nine reference outputs
Up to two sets of four low-skew outputs
Operating voltages of 3.3 V
Advanced, low-power CMOS process
For one output clock, use the ICS341. For two output
clocks, see the ICS342. For three output clocks, see
the ICS343. For more than three outputs, see the
ICS345 or ICS348.
•
Available in Pb (lead) free packaging
Block Diagram
VDD
3
S 2:S 0
3
OTP
ROM
w ith
P LL
V alues
P LL1 with
S pread
S pectrum
D ivide
Logic
and
O utput
E nable
C ontrol
C LK 1
C LK 2
C LK 3
P LL2
C LK 4
C LK 5
C LK 6
C LK 7
C LK 8
C rystal or
clock input
X 1/IC LK
C rystal
O scillator
X2
P LL3
C LK 9
E xternal capacitors are
required w ith a crystal input.
GND
2
PD TS
MDS 345 D
Integrated Circuit Systems, Inc.
●
1
525 Race Street, San Jose, CA 95126
●
Revision 090704
tel (408) 297-1201
●
www.icst.com
ICS345
Triple PLL Field Programmable SS VersaClock Synthesizer
Pin Assignment
X1/ICLK
S0
S1
CLK9
VDD
GND
CLK1
CLK2
CLK3
CLK4
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
X2
VDD
PDTS
S2
VDD
GND
CLK5
CLK6
CLK7
CLK8
20-pin (150 mil) SSOP (QSOP)
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Pin
Name
X1/ICLK
S0
S1
CLK9
VDD
GND
CLK1
CLK2
CLK3
CLK4
CLK8
CLK7
CLK6
CLK5
GND
VDD
S2
PDTS
VDD
X2
Pin
Type
XI
Input
Input
Output
Power
Power
Output
Output
Output
Output
Output
Output
Output
Output
Power
Power
Input
Input
Power
XO
Pin Description
Crystal input. Connect this pin to a crystal or external input clock.
Select pin 0. Internal pull-up resistor.
Select pin 1. Internal pull-up resistor.
Output clock 9. Weak internal pull-down when tri-state.
Connect to +3.3 V.
Connect to ground.
Output clock 1. Weak internal pull-down when tri-state.
Output clock 2. Weak internal pull-down when tri-state.
Output clock 3. Weak internal pull-down when tri-state.
Output clock 4. Weak internal pull-down when tri-state.
Output clock 8. Weak internal pull-down when tri-state.
Output clock 7. Weak internal pull-down when tri-state.
Output clock 6. Weak internal pull-down when tri-state.
Output clock 5. Weak internal pull-down when tri-state.
Connect to ground.
Connect to +3.3 V.
Select pin 2. Internal pull-up resisitor.
Power-down tri-state. Powers down entire chip and tri-states clock outputs
when low. Internal pull-up resisitor.
Connect to +3.3 V.
Crystal Output. Connect this pin to a crystal. Float for clock input.
MDS 345 D
Integrated Circuit Systems, Inc.
●
2
525 Race Street, San Jose, CA 95126
●
Revision 090704
tel (408) 297-1201
●
www.icst.com
ICS345
Triple PLL Field Programmable SS VersaClock Synthesizer
External Components
Series Termination Resistor
Clock output traces over one inch should use series
termination. To series terminate a 50Ω trace (a
commonly used trace impedance), place a 33Ω resistor
in series with the clock line, as close to the clock output
pin as possible. The nominal impedance of the clock
output is 20Ω.
spaces, instead they should be separated and away
from other traces.
3) To minimize EMI, the 33Ω series termination resistor
(if needed) should be placed close to the clock output.
4) An optimum layout is one with all components on the
same side of the board, minimizing vias through other
signal layers.
ICS345 Configuration Capabilities
The architecture of the ICS345 allows the user to easily
configure the device to a wide range of output
frequencies, for a given input reference frequency.
The frequency multiplier PLL provides a high degree of
precision. The M/N values (the multiplier/divide values
available to generate the target VCO frequency) can be
set within the range of M = 1 to 2048 and N = 1 to 1024.
The ICS345 also provides separate output divide
values, from 2 through 20, to allow the two output clock
banks to support widely differing frequency values from
the same PLL.
Each output frequency can be represented as:
OutputFreq
REFFreq
-------------------------------------
-
OutputDivide
----
-
⋅
M
N
Decoupling Capacitors
As with any high-performance mixed-signal IC, the
ICS345 must be isolated from system power supply
noise to perform optimally.
Decoupling capacitors of 0.01µF must be connected
between each VDD and the PCB ground plane.
Crystal Load Capacitors
The device crystal connections should include pads for
small capacitors from X1 to ground and from X2 to
ground. These capacitors are used to adjust the stray
capacitance of the board to match the nominally
required crystal load capacitance. Because load
capacitance can only be increased in this trimming
process, it is important to keep stray capacitance to a
minimum by using very short PCB traces (and no vias)
been the crystal and device. Crystal capacitors must be
connected from each of the pins X1 and X2 to ground.
The value (in pF) of these crystal caps should equal
(C
L
-6 pF)*2. In this equation, C
L
= crystal load
capacitance in pF. Example: For a crystal with a 16 pF
load capacitance, each crystal capacitor would be 20
pF [(16-6) x 2] = 20.
=
ICS VersaClock Software
ICS applies years of PLL optimization experience into a
user friendly software that accepts the user’s target
reference clock and output frequencies and generates
the lowest jitter, lowest power configuration, with only a
press of a button. The user does not need to have prior
PLL experience or determine the optimal VCO
frequency to support multiple output frequencies.
VersaClock software quickly evaluates accessible VCO
frequencies with available output divide values and
provides an easy to understand, bar code rating for the
target output frequencies. The user may evaluate
output accuracy, performance trade-off scenarios in
seconds.
PCB Layout Recommendations
For optimum device performance and lowest output
phase noise, the following guidelines should be
observed.
1) Each 0.01µF decoupling capacitor should be
mounted on the component side of the board as close
to the VDD pin as possible. No vias should be used
between decoupling capacitor and VDD pin. The PCB
trace to VDD pin should be kept as short as possible,
as should the PCB trace to the ground via.
2) The external crystal should be mounted just next to
the device with short traces. The X1 and X2 traces
should not be routed next to each other with minimum
Spread Spectrum Modulation
The ICS345 utilizes frequency modulation (FM) to
distribute energy over a range of frequencies. By
modulating the output clock frequencies, the device
effectively lowers energy across a broader range of
MDS 345 D
Integrated Circuit Systems, Inc.
●
3
525 Race Street, San Jose, CA 95126
●
Revision 090704
tel (408) 297-1201
●
www.icst.com
ICS345
Triple PLL Field Programmable SS VersaClock Synthesizer
frequencies; thus, lowering a system’s electromagnetic
interference (EMI). The modulation rate is the time from
transitioning from a minimum frequency to a maximum
frequency and then back to the minimum.
Spread Spectrum Modulation can be applied as either
“center spread” or “down spread”. During center spread
modulation, the deviation from the target frequency is
equal in the positive and negative directions. The
effective average frequency is equal to the target
frequency. In applications where the clock is driving a
component with a maximum frequency rating, down
spread should be applied. In this case, the maximum
frequency, including modulation, is the target
frequency. The effective average frequency is less than
the target frequency.
The ICS345 operates in both center spread and down
spread modes. For center spread, the frequency can
be modulated between +/- 0.125% to +/-2.0%. For
down spread, the frequency can be modulated
between -0.25% to -4.0%.
Both output frequency banks will utilize identical spread
spectrum percentage deviations and modulation rates,
if a common VCO frequency can be identified.
Spread Spectrum Modulation Rate
The spread spectrum modulation frequency applied to
the output clock frequency may occur at a variety of
rates. For applications requiring the driving of
“down-circuit” PLLs, Zero Delay Buffers, or those
adhering to PCI standards, the spread spectrum
modulation rate should be set to 30-33 kHz. For other
applications, a 120 kHz modulation option is available.
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS345. These ratings, which
are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of the
device at these or any other conditions above those indicated in the operational sections of the
specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can
affect product reliability. Electrical parameters are guaranteed only over the recommended operating
temperature range.
Parameter
Supply Voltage, VDD
Inputs
Clock Outputs
Storage Temperature
Soldering Temperature
Junction Temperature
Condition
Referenced to GND
Referenced to GND
Referenced to GND
Max 10 seconds
Min.
-0.5
-0.5
-65
Typ.
Max.
7
VDD+0.5
VDD+0.5
150
260
125
Units
V
V
V
°C
°C
°C
MDS 345 D
Integrated Circuit Systems, Inc.
●
4
525 Race Street, San Jose, CA 95126
●
Revision 090704
tel (408) 297-1201
●
www.icst.com
ICS345
Triple PLL Field Programmable SS VersaClock Synthesizer
Recommended Operation Conditions
Parameter
Ambient Operating Temperature (ICS345RP)
Ambient Operating Temperature (ICS345RIP)
Power Supply Voltage (measured in respect to GND)
Power Supply Ramp Time
Min.
0
-40
+3.15
Typ.
Max.
+70
+85
Units
°C
°C
V
ms
+3.3
+3.45
4
DC Electrical Characteristics
Unless stated otherwise,
VDD = 3.3V ±5%,
Ambient Temperature -40 to +85°C
Parameter
Operating Voltage
Symbol
VDD
Conditions
Configuration Dependent -
See VersaClock
TM
Estimates
Min.
3.15
Typ.
Max.
3.45
Units
V
mA
Operating Supply Current
Input High Voltage
IDD
Nine 33.3333 MHz outs,
PDTS = 1, no load, Note 1
PDTS = 0, no load, Note 1
S2:S0
S2:S0
VDD-0.5
2
23
20
0.4
0.4
mA
µA
V
V
V
V
V
VDD/2-1
V
V
V
0.4
V
mA
Ω
kΩ
kΩ
pF
Input High Voltage
Input Low Voltage
Input High Voltage, PDTS
Input Low Voltage, PDTS
Input High Voltage
Input Low Voltage
Output High Voltage
(CMOS High)
Output High Voltage
Output Low Voltage
Short Circuit Current
Nominal Output
Impedance
Internal pull-up resistor
Internal pull-down
resistor
Input Capacitance
V
IH
V
IL
V
IH
V
IL
V
IH
V
IL
V
OH
V
OH
V
OL
I
OS
Z
O
R
PUS
R
PD
C
IN
ICLK
ICLK
I
OH
= -4 mA
I
OH
= -12 mA
I
OL
= 12 mA
VDD/2+1
VDD-0.4
2.4
±70
20
S2:S0, PDTS
CLK outputs
Inputs
250
525
4
Note 1: Example with 25 MHz crystal input with nine outputs of 33.3 MHz, no load, and VDD = 3.3 V.
MDS 345 D
Integrated Circuit Systems, Inc.
●
5
525 Race Street, San Jose, CA 95126
●
Revision 090704
tel (408) 297-1201
●
www.icst.com
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