DATASHEET
PRECISION AUDIO CLOCK SOURCE
Description
The ICS661 provides synchronous clock generation for
audio sampling clock rates derived from an MPEG stream,
or can be used as a standalone clock source with a 27 MHz
crystal. The device uses the latest PLL technology to
provide excellent phase noise and long term jitter
performance for superior synchronization and S/N ratio.
Please contact IDT if you have a requirement for an input
and output frequency not included here - we can rapidly
modify this product to meet special requirements.
ICS661
Features
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•
•
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Packaged in 16-pin TSSOP
Pb (lead) free package, RoHS compliant
Clock or crystal input
Low phase noise
Low jitter
Exact (0 ppm) multiplication ratios
Reference clock output available
Support for 256, 384, 512, and 768 times sampling rate
Block Diagram
VDD (P2)
VDD (P3)
VDDO
VDDR
X2
Crystal
Oscillator
REF
X1/REFIN
SELIN
S3:0
PLL Clock
Synthesis
4
CLK
GND (P13)
GND (P6)
GND (P5)
IDT™ / ICS™
PRECISION AUDIO CLOCK SOURCE
1
ICS661
REV F 051310
ICS661
PRECISION AUDIO CLOCK SOURCE
CLOCK SYNTHESIZER
Pin Assignment
X1/REFIN
VDD
VDD
S0
GND
GND
S3
S2
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
X2
REF
VDDR
GND
SELIN
VDDO
S1
CLK
Output Clock Selection Table
S3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
S2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
S1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
S0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Input
Frequency
(MHz)
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
27
Output
Frequency
(MHz)
8.192
11.2896
12.288
24.576
12.288
16.9344
18.432
36.864
16.384
22.5792
24.576
49.152
24.576
33.8688
36.864
73.728
16-pin 4.40 mil body, 0.50 mm pitch TSSOP
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Pin
Name
X1/REFIN
VDD
VDD
S0
GND
GND
S3
S2
CLK
S1
VDDO
SELIN
GND
VDDR
REF
X2
Pin
Type
Input
Power
Power
Input
Power
Power
Input
Input
Output
Input
Power
Input
Power
Power
Output
Input
Power supply for crystal oscillator.
Power supply for PLL.
Pin Description
Connect this pin to a crystal or clock input
Output frequency selection. Determines output frequency per table above. On chip pull-up.
Connect to ground.
Ground for output stage.
Output frequency selection. Determines output frequency per table above. On chip pull-up.
Output frequency selection. Determines output frequency per table above. On chip pull-up.
Clock output.
Output frequency selection. Determines output frequency per table above. On chip pull-up.
Power supply for output stage.
Low for clock input, high for crystal. On chip pull-up.
Connect to ground.
Power supply for reference output. Ground to turn off REF.
Reference clock output.
Connect this pin to a crystal. Leave open if using a clock input.
IDT™ / ICS™
PRECISION AUDIO CLOCK SOURCE
2
ICS661
REV F 051310
ICS661
PRECISION AUDIO CLOCK SOURCE
CLOCK SYNTHESIZER
Application Information
Series Termination Resistor
Clock output traces 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
.
capacitance of the board to match the nominally required
crystal load capacitance. To reduce possible noise pickup,
use very short PCB traces (and no vias) been the crystal
and device.
The value of the load capacitors can be roughly determined
by the formula C = 2(C
L
- 6) where C is the load capacitor
connected to X1 and X2, and C
L
is the specified value of the
load capacitance for the crystal. A typical crystal C
L
is 18 pF,
so C = 2(18 - 6) = 24 pF. Because these capacitors adjust
the stray capacitance of the PCB, check the output
frequency using your final layout to see if the value of C
should be changed.
Decoupling Capacitors
As with any high performance mixed-signal IC, the ICS661
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. To further
guard against interfering system supply noise, the ICS661
should use one common connection to the PCB power
plane as shown in the diagram on the next page. The ferrite
bead and bulk capacitor help reduce lower frequency noise
in the supply that can lead to output clock phase modulation.
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. Distance of the ferrite bead and bulk decoupling
from the device is less critical.
2) The external crystal should be mounted 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 and obtain the best signal integrity, the
33Ω series termination resistor 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 (the ferrite bead and bulk decoupling capacitor can be
mounted on the back). Other signal traces should be routed
away from the ICS661. This includes signal traces just
underneath the device, or on layers adjacent to the ground
plane layer used by the device.
Recommended Power Supply Connection for
Optimal Device Performance
V D D P in
C onnection to 3.3V
P ow er P lane
Ferrite
Bead
V D D P in
B ulk D ecoupling C apacitor
(such as 1 F Tantalum )
V D D P in
0.01
F D ecoupling C apacitors
All power supply pins must be connected to the same
voltage, except VDDR and VDDO may be connected to a
lower voltage in order to change the output level. If the
reference output is not used, ground VDDR.
Crystal Load Capacitors
If a crystal is used, the device crystal connections should
include pads for capacitors from X1 to ground and from X2
to ground. These capacitors are used to adjust the stray
IDT™ / ICS™
PRECISION AUDIO CLOCK SOURCE
3
ICS661
REV F 051310
ICS661
PRECISION AUDIO CLOCK SOURCE
CLOCK SYNTHESIZER
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS661. These ratings, which are
standard values for IDT 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.
Item
Supply Voltage, VDD
All Inputs and Outputs
Ambient Operating Temperature
Storage Temperature
Junction Temperature
Soldering Temperature
5.5 V
Rating
-0.5 V to VDD+0.5 V
-40 to +85° C
-65 to +150° C
125° C
260° C
Recommended Operation Conditions
Parameter
Ambient Operating Temperature
Power Supply Voltage (measured in respect to GND)
Min.
-40
+3.0
Typ.
Max.
+85
+3.6
Units
°
C
V
DC Electrical Characteristics
Unless stated otherwise,
VDD = 3.3 V ±10%,
Ambient Temperature -40 to +85° C
Parameter
Operating Voltage
Symbol
VDD
VDDO
VDDR
Conditions
Min.
3.0
1.8
1.8
2
Typ.
Max.
3.6
VDD
VDD
0.8
Units
V
V
V
V
V
V
V
Input High Voltage
Input Low Voltage
Output High Voltage
Output High Voltage
Output Low Voltage
Supply Current
Short Circuit Current
Nominal Output Impedance
Input Capacitance
Internal Pull-up Resistor
V
IH
V
IL
V
OH
V
OH
V
OL
IDD
I
OS
Z
OUT
Input pins
I
OH
= -4 mA
I
OH
= -20 mA
I
OL
= 20 mA
No Load
Each output
VDD-0.4
2.4
0.4
25
±65
20
7
120
V
mA
mA
Ω
pF
kΩ
IDT™ / ICS™
PRECISION AUDIO CLOCK SOURCE
4
ICS661
REV F 051310
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