DATASHEET
SPREAD SPECTRUM CLOCK GENERATOR
Description
The ICS7151A-50 is a clock generator for EMI
(Electromagnetic Interference) reduction. Spectral peaks
are attenuated by modulating the system clock frequency.
Down or center spread profiles are selectable. Down
spread will not exceed the maximum frequency of an
unspread clock, and center spread does not change the
average operating frequency of the system
IDT offers many other clocks for computers and computer
peripherals. Consult IDT when you need to remove crystals
and oscillators from your board.
ICS7151A-50
Features
•
•
•
•
•
•
Operating voltage of 3.3 V ±0.3 V
Packaged in 8-pin SOIC
Available in Pb (lead) free package
Input frequency range of 16.5 to 33.4 MHz
Output frequency ranges of 8.3 to 16.7 MHz
Provides a spread spectrum clock output (±0.5%, ±1.5%
center spread; -1.0%, -3.0% down spread)
•
Multiplication rate of x1/2
•
Advanced, low-power CMOS process
•
Pin compatible with the Fujitsu MB88151-500
NOTE: EOL for non-green parts to occur on 5/13/10
per PDN U-09-01
Block Diagram
VDD
S1:0
2
ENS
PLL Clock
Synthesis
and Spread
Spectrum
Circuitry
Clock Buffer/
Crystal
Ocsillator
CKOUT
XIN
XOUT
External caps required with crystal for
accurate tuning of the clock
GND
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
1
ICS7151A-50
REV B 110409
ICS7151A-50
SPREAD SPECTRUM CLOCK GENERATOR
SSCG
Pin Assignment
XIN
GND
S0
S1
1
2
3
4
8
7
6
5
8 pin (150 mil) SOIC
XOUT
VDD
ENS
CKOUT
Spread Direction and Percentage
Select Table
S1
Pin 4
0
0
1
1
ENS
(note 1)
S0
Pin 3
0
1
0
1
Spread
Direction
Center
Center
Down
Down
Modulation
No Modulation
Modulation
Spread
Percentage (%)
±1.5
±0.5
-1.0
-3.0
0
1
Notes:
1. Pin 1 has a pull-up resistor.
Pin Descriptions
Pin
Number
Pin
Name
Pin Type
Pin Description
1
2
3
4
5
6
7
8
XIN
GND
S0
S1
CKOUT
ENS
VDD
XOUT
Input
Power
Input
Input
Output
Input
Power
Output
Crystal pin/clock input pin.
Connect to ground.
Select pin 0. Spread modulation select.
Select pin 1. Spread modulation select.
Clock output.
Modulation enable. Internal pull-up resistor.
Connect to +3.3 V.
Crystal connection pin.
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
2
ICS7151A-50
REV B 110409
ICS7151A-50
SPREAD SPECTRUM CLOCK GENERATOR
SSCG
External Components
The ICS7151A-50 requires a minimum number of external
components for proper operation.
Crystal caps (pF) = (C
L
- 6) x 2
In the equation, C
L
is the crystal load capacitance. So, for a
crystal with a 16 pF load capacitance, two 20 pF [(16-6) x 2]
capacitors should be used.
Decoupling Capacitor
A decoupling capacitor of 0.01µF must be connected
between GND and VDD on pins 2 and 7, 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.
Spread Spectrum Profile
The ICS7151A-50 low EMI clock generator uses a triangular
frequency modulation profile for optimal down stream
tracking of zero delay buffers and other PLL devices. The
frequency modulation amplitude is constant with variations
of the input frequency.
Series Termination Resistor
Series termination should be used on the clock output. To
series terminate a 50Ω trace (a commonly used trace
impedance) place a 27Ω resistor in series with the clock line,
as close to the clock output pin as possible. The nominal
impedance of the clock output is 25Ω
.
Modulation Rate
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 27Ω 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
ICS7151A-50. This includes signal traces just underneath
the device, or on layers adjacent to the ground plane layer
used by the device.
Frequency
Time
Crystal Information
The crystal used should be a fundamental mode (do not use
third overtone), parallel resonant. Crystal capacitors should
be connected from pins X1 to ground and X2 to ground to
optimize the initial accuracy. The value of these capacitors
is given by the following equation:
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
3
ICS7151A-50
REV B 110409
ICS7151A-50
SPREAD SPECTRUM CLOCK GENERATOR
SSCG
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS7151A-50. 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 (referenced to GND)
Ambient Operating Temperature
Storage Temperature
Junction Temperature
Soldering Temperature
Overshoot (V
IOVER
)
Undershoot (V
IUNDER
)
-0.5 to 4.0 V
Rating
-0.5 V to VDD+0.5 V
-40 to +85° C
-55 to +125° C
-40 to +125° C
260° C
VDD + 1.0 V (t
OVER
< 50 ns)
GND - 1.0 V (t
UNDER
< 50 ns)
Overshoot/Undershoot
t
UNDER
< 50 ns
V
IOVER
< V
DD
+ 1.0 V
V
DD
GND
V
IUNDER
< GND - 1.0 V
Input pin
t
OVER
< 50 ns
Recommended Operation Conditions
Parameter
Ambient Operating Temperature
Power Supply Voltage (measured in respect to GND)
Min.
-40
+3.0
Typ.
3.3
Max.
+85
3.6
Units
°
C
V
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
4
ICS7151A-50
REV B 110409
ICS7151A-50
SPREAD SPECTRUM CLOCK GENERATOR
SSCG
DC Electrical Characteristics
Unless stated otherwise,
VDD = 3.3 V ±0.3 V,
Ambient Temperature -40 to +85° C
Parameter
Operating Voltage
Supply Current
Input Frequency
Input High Voltage
Input Low Voltage
Output High Voltage
Output Low Voltage
Input Capacitance
Symbol
VDD
IDD
Conditions
No load, at 3.3 V,
output = 24 MHz
Min.
3.0
Typ.
3.3
10
Max.
3.6
14
33.4
VDD + 0.3
VDD * 0.20
0.4
16
15
10
7
Units
V
mA
MHz
V
V
V
V
pF
pF
pF
pF
kΩ
16.5
V
IH
V
IL
V
OH
V
OL
C
IN
XIN, S0, S1, ENS
XIN, S0, S1, ENS
CKOUT, I
OH
= -4 mA
CKOUT, I
OL
= 4 mA
XIN, S0, S1, ENS
CKOUT, 8.3 to 66.7
MHz
VDD * 0.8
0.0
2.0
Load Capacitance
C
L
CKOUT, 66.7 to 100
MHz
CKOUT, 100 to 133.4
MHz
Input Pull-up Resistor
R
PU
ENS
100
240
400
AC Electrical Characteristics
Unless stated otherwise,
VDD = 3.3 V ±0.3 V,
Ambient Temperature -40 to +85° C
Parameter
Oscillation Frequency
Input Frequency
Output Frequency
Input Clock Duty Cycle
Output Clock Duty Cycle
Output Slew Rate
Cycle to Cycle Jitter
Lock Time
Modulation Frequency
Symbol
f
X
f
IN
f
OUT
Conditions
Fundamental
oscillation
XIN
CKOUT, 2-frequency
division
XIN, 16.5 to 33.4 MHz
CKOUT, 1.5 V
CKOUT, 0.4 to 2.4 V,
load capacitance 15 pF
Min.
16.5
16.5
8.3
40
40
0.5
Typ.
Max.
33.4
33.4
16.7
Units
MHz
MHz
MHz
%
%
V/ns
ps
ms
kHz
50
TBD
TBD
2
33
60
60
3.0
200
5
t
DCC
t
JC
t
LK
f
MOD
No load, standard
deviation
CKOUT
CKOUT=TBD
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
5
ICS7151A-50
REV B 110409
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