DATASHEET
QUAD PLL FIELD PROGRAMMABLE VERSACLOCK SYNTHESIZER
Description
The ICS348 field programmable clock synthesizer
generates up to 9 high-quality, high-frequency clock outputs
including multiple reference clocks from a low frequency
crystal or clock input. The ICS348 has 4 independent
on-chip PLLs and is designed to replace crystals and
crystal oscillators in most electronic systems.
Using IDT’s VersaClock software to configure PLLs and
outputs, the ICS348 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.
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 ICS348 is also available in factory programmed custom
versions for high-volume applications.
TM
ICS348
Features
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Packaged as 20-pin SSOP (QSOP) (Pb-free)
Eight addressable registers
Replaces multiple crystals and oscillators
Output frequencies up to 200 MHz at 3.3V
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 (8-pin). For two
output clocks, use the ICS342 (8-pin). For three output
clocks, use the ICS343 (8-pin). For more than three
outputs, use the ICS345 or ICS348.
Block Diagram
V DD
3
S 2:S 0
3
O TP
ROM
w ith
P LL
V alues
P LL1
CLK1
CLK2
P LL2
CLK3
Divide
Logic
and
Output
Enable
Control
CLK4
CLK5
CLK6
CLK7
CLK8
CLK9
P LL3
C rystal or
clock input
X 1/IC LK
C rystal
O scillator
X2
GND
2
P LL4
E xternal capacitors are
required w ith a crystal input.
P D TS
IDT®
QUAD PLL FIELD PROGRAMMABLE VERSACLOCK SYNTHESIZER
1
ICS348
REV N 090613
ICS348
QUAD PLL FIELD PROGRAMMABLE VERSACLOCK SYNTHESIZER
EPROM CLOCK 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
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 resistor.
Power down tri-state. Powers down entire chip and tri-states clock outputs
when low. Internal pull-up resistor.
Connect to +3.3 V.
Crystal Output. Connect this pin to a fundamental crystal. Float for clock input.
IDT®
QUAD PLL FIELD PROGRAMMABLE VERSACLOCK SYNTHESIZER
2
ICS348
REV N 090613
ICS348
QUAD PLL FIELD PROGRAMMABLE VERSACLOCK SYNTHESIZER
EPROM CLOCK SYNTHESIZER
External Components
Series Termination Resistor
Clock output traces over one inch should use series
termination. To series terminate a 50 trace (a commonly
used trace impedance), place a 33 resistor in series with
the clock line, as close to the clock output pin as possible.
The nominal impedance of the clock output is 20.
ICS348 Configuration Capabilities
The architecture of the ICS348 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 ICS348 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
Decoupling Capacitors
As with any high-performance mixed-signal IC, the ICS348
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) between 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.
REFFreq
-------------------------------------
-
OutputDivide
----
-
M
N
IDT VersaClock Software
IDT 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 spaces, instead
they should be separated and away from other traces.
3) To minimize EMI, the 33 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.
IDT®
QUAD PLL FIELD PROGRAMMABLE VERSACLOCK SYNTHESIZER
Using VersaClock Products with an Input Clock
Source
In order to ensure proper startup with an input clock rather
than a crystal, the supply voltage must be within the
operating range (3.3V ±10%) and the input signal must be
stable and free from glitching. The input clock must provide
pulses of at least 20ns, and no more than 500ns, for at least
160 clock cycles without any interruptions to the clock or
power during this period. It may take up to 4ms for output
frequencies to reach their target frequency values.
An alternative method is to have the PDTS pin asserted low
while power supplies and clock sources stabilize.Once the
power supply and input clock source are constant and within
the acceptable frequency range, bring PDTS high. This
approach is preferred if the clock source is derived from
another PLL, or the source oscillator produces
unpredictable output pulses prior to stabilization. No
considerations need to be taken when using a crystal input
source with VersaClock products.
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ICS348
REV N 090613
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