DATASHEET
LOW EMI CLOCK GENERATOR
Description
The ICS181-51 generates a low EMI output clock from
a clock or crystal input. The device uses IDT’s
proprietary mix of analog and digital Phase-Locked
Loop (PLL) technology to spread the frequency
spectrum of the output, thereby reducing the frequency
amplitude peaks by several dB.
The ICS181-51 offers center spread selection of
+/-0.625% and +/-1.875%. Refer to the MK1714-01/02
for the widest selection of input frequencies and
multipliers.
IDT offers a complete line of EMI reducing clock
generators. Consult us when you need to remove
crystals and oscillators from your board.
ICS181-51
Features
•
•
•
•
Pin and function compatible to Cypress W181-51
Packaged in 8-pin SOIC
Provides a spread spectrum output clock
Accepts a clock input and provides same frequency
dithered output
•
Input frequency of 28 to 75 MHz for Clock input
•
Peak reduction by 7dB - 14dB typical on 3rd - 19th
odd harmonics
•
Spread percentage selection for +/-0.625% and
+/-1.875%
•
Operating voltage of 3.3 V and 5 V
•
Advanced, low-power CMOS process
Block Diagram
VDD
FS2:1
SS%
PLLClock
Synthesis
andSpread
Spectrum
Circuitry
CLK
X1/CLKIN
X2
ClockBuffer/
Crystal
Oscillator
GND
IDT™ / ICS™
LOW EMI CLOCK GENERATOR
1
ICS181-51
REV C 051310
ICS181-51
LOW EMI CLOCK GENERATOR
SSCG
Pin Assignment
X1/CLKIN
X2
GND
SS%
1
2
3
4
8
7
6
5
FS2
FS1
VDD
CLKOUT
Spread Spectrum Select Table
SS%
(Pin 4)
0
1
Spread
Direction
Center
Center
Spread
Percentage (%)
+/-0.625%
+/1.875%
8 pin (150 mil) SOIC
0 = connect to GND
1 = connect directly to VDD
Note: SS% pin has an internal pull-up resistor
Frequency Range Selection Table
FS2
(Pin 8)
FS1
(Pin 7)
Frequency
Range Selection
(MHz)
28-38
38-48
46-60
58-75
0
0
1
1
0
1
0
1
Pin Descriptions
Pin
Number
Pin
Name
Pin Type
Pin Description
1
2
3
4
5
6
7
8
X1/CLKIN
X2
GND
SS%
CLKOUT
VDD
FS1
FS2
Input
Output
Power
Input
Output
Power
Input
Input
Crystal or Clock Input.
Crystal output. Float for a clock input.
Connect to ground.
Select pin for spread amount. See table above. Internal pull-up resistor.
Spread spectrum clock output per table above.
Connect to 3.3 V or 5 V.
Select pin for input frequency. See table above. Internal pull-up resistor.
Select pin for input frequency. See table above. Internal pull-up resistor.
IDT™ / ICS™
LOW EMI CLOCK GENERATOR
2
ICS181-51
REV C 051310
ICS181-51
LOW EMI CLOCK GENERATOR
SSCG
External Components
The ICS181-51 requires a minimum number of external
components for proper operation.
PCB Layout Recommendations
For optimum device performance and lowest output
phase noise, the following guidelines should be
observed.
1) The 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 the
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) To minimize EMI the 33
Ω
series termination resistor,
if needed, should be placed close to the clock output.
3) An optimum layout is one with all components on the
same side of the board, minimizing vias through other
signal layers. Other signal traces should be routed away
from the ICS181-51. This includes signal traces just
underneath the device, or on layers adjacent to the
ground plane layer used by the device.
Decoupling Capacitor
A decoupling capacitor of 0.01µF must be connected
between VDD and GND on pins 6 and 3, as close to
these pins as possible. For optimum device
performance, the decoupling capacitor should be
mounted on the component side of the PCB. Avoid the
use of vias in the decoupling circuit.
Series Termination Resistor
When the PCB trace between the clock output and the
load is over 1 inch, series termination should be used.
To series terminate a 50
Ω
trace (a commonly used trace
impedance) place a 33
Ω
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
Ω
.
value of these capacitors is given by the following
equation:
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS181-51. 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
7V
Rating
-0.5 V to VDD+0.5 V
0 to +70
°
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.
0
+3.135
Typ.
Max.
+70
+5.5
Units
°
C
V
IDT™ / ICS™
LOW EMI CLOCK GENERATOR
3
ICS181-51
REV C 051310
ICS181-51
LOW EMI CLOCK GENERATOR
SSCG
AC Electrical Characteristics
Unless stated otherwise,
VDD = 3.3 V±5% or 5 V±10%
, Ambient Temperature 0 to +70
°
C, C
L
=15 pf
Parameter
Input/Output Clock Frequency
Input Crystal Frequency
Input Clock Duty Cycle
Output Clock Duty Cycle
Output Rise Time
Output Fall Time
Jitter
Note 1: Measured with 15pF load
Symbol
Conditions
Min.
28
28
Typ.
Max. Units
75
40
60
MHz
MHz
%
%
ns
ns
ps
Time above VDD/2
Note 1
t
OR
t
OF
0.8 to 2.4 V, note 1
2.4 to 0.8 V, note 1
Cycle-to-cycle
40
40
50
2
2
250
60
5
5
300
Thermal Characteristics
Parameter
Thermal Resistance Junction to
Ambient
Symbol
θ
JA
θ
JA
θ
JA
θ
JC
Conditions
Still air
1 m/s air flow
3 m/s air flow
Min.
Typ.
150
140
120
40
Max. Units
°
C/W
°
C/W
°
C/W
°
C/W
Thermal Resistance Junction to Case
Marking Diagram (Pb free)
8
5
181M51LF
######
YYWW
1
4
Notes:
1. ###### is the lot number.
2. YYWW is the last two digits of the year and week that the part was assembled.
3. “LF” denotes Pb (lead) free package.
4. Bottom Marking: country of origin.
IDT™ / ICS™
LOW EMI CLOCK GENERATOR
5
ICS181-51
REV C 051310
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