DATASHEET
SPREAD SPECTRUM CLOCK GENERATOR
Description
The ICS7151-10, -20, -40, and -50 are clock generators for
EMI (Electro Magnetic Interference) reduction (see below
for frequency ranges and multiplier ratios). Spectral peaks
can be attenuated by slightly modulating the oscillation
frequency. Both down and center spread profiles are
selectable. Down spread maintains an average frequency
less than an unspread clock, and will not exceed the
maximum frequency of an unspread clock.
ICS7151
Features
•
•
•
•
•
Operating voltage of 3.3 V ±0.3 V
Packaged in 8-pin SOIC
Pb (lead) free package, RoHS compliant
Input frequency range of 16.5 to 33.4 MHz
Output frequency ranges of 8.3 to 16.7 MHz, 16.5 to 33.4
MHz, 33.3 to 66.7 MHz, 66.6 to 133.4 MHz
center spread; -1.0%, -3.0% down spread)
•
Provides a spread spectrum clock output (±0.5%, ±1.5%
•
Multiplication rates of x1/2, x1, x2, and x4
•
Advanced, low-power CMOS process
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
Product Lineup
Product
Input Frequency Range
Multiplier Ratio
Output Frequency Range
ICS7151M-10, ICS7151MI-10
ICS7151M-20, ICS7151MI-20
ICS7151M-40, ICS7151MI-40
ICS7151M-50, ICS7151MI-50
16.5 MHz to 33.4 MHz
16.5 MHz to 33.4 MHz
16.5 MHz to 33.4 MHz
16.5 MHz to 33.4 MHz
X1
X2
X4
X1/2
16.5 MHz to 33.4 MHz
33.3 MHz to 66.7 MHz
66.6 MHz to 133.4 MHz
8.3 MHz to 16.7 MHz
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
1
ICS7151
REV J 051310
ICS7151
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
(note1)
0
0
1
1
ENS
(note 2)
S0
Pin 3
(note1)
0
1
0
1
Spread
Direction
Center
Center
Down
Down
Spread
Percentage (%)
±1.5
±0.5
-1.0
-3.0
Spread Spectrum
OFF
ON
0
1
Notes:
1. The modulation rate varies with input frequency.
2. Spread will default to ON when ENS pin is left open.
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
Resonator connection pin/clock input pin.
Connect to ground.
Select pin 0. Modulation rate setting pin.
Select pin 1. Modulation rate setting pin.
Modulated clock output pin.
Modulation enable setting pin. Internal pull-up resistor.
Connect to +3.3 V.
Resonator connection pin.
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
2
ICS7151
REV J 051310
ICS7151
SPREAD SPECTRUM CLOCK GENERATOR
SSCG
External Components
The ICS7151 requires a minimum number of external
components for proper operation.
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.
Spread Spectrum Profile
Decoupling Capacitor
A decoupling capacitor of 0.01µF must be connected
between GND and VDD on pin 7, as close to this pin 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.
The ICS7151 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
ICS7151. 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:
Crystal caps (pF) = (C
L
- 6) x 2
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
3
ICS7151
REV J 051310
ICS7151
SPREAD SPECTRUM CLOCK GENERATOR
SSCG
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS7151. 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
)
7V
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
ICS7151
REV J 051310
ICS7151
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 High Voltage
Input Low Voltage
Output High Voltage
Output Low Voltage
Input Capacitance
Symbol
VDD
IDD
V
IH
V
IL
V
OH
V
OL
C
IN
Conditions
No load, at 3.3 V
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
Min.
3.0
VDDx0.8
0.0
VDD-0.5
Typ.
3.3
10
Max.
3.6
20
VDD + 0.3
VDDx0.20
0.4
16
15
10
7
Units
V
mA
V
V
V
V
pF
pF
pF
pF
kΩ
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
Input Crystal Frequency
Input Clock Frequency
Symbol
f
IN
Conditions
Min.
16.5
16.5
Typ.
Max.
33.4
33.4
33.4
66.7
133.4
16.7
Units
MHz
MHz
MHz
MHz
MHz
MHz
%
%
V/ns
CKOUT, Multiply by 1
(ICS7151-10)
CKOUT, Multiply by 2
(ICS7151-20)
CKOUT, Multiply by 4
(ICS7151-40)
CKOUT, 2-frequency
division (ICS7151-50)
Input Clock Duty Cycle
Output Clock Duty Cycle
Output Slew Rate
t
DCC
XIN, 16.5 to 33.4 MHz
CKOUT, 1.5 V
CKOUT, 0.4 to 2.4 V,
CL = 15 pF
16.5
33.3
66.6
8.3
40
40
0.5
50
Output Frequency
f
OUT
60
60
3.0
IDT™ / ICS™
SPREAD SPECTRUM CLOCK GENERATOR
5
ICS7151
REV J 051310
编程基础
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