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SM560 Datasheet(PDF) 4 Page - Cypress Semiconductor

Part No. SM560
Description  Spread Spectrum Clock Generator
Download  8 Pages
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Maker  CYPRESS [Cypress Semiconductor]
Homepage  http://www.cypress.com
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SM560 Datasheet(HTML) 4 Page - Cypress Semiconductor

   
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SM560
Document #: 38-07020 Rev. *E
Page 4 of 8
Absolute Maximum Ratings[1]
Supply Voltage (VDD): .................................... –0.5V to +6.0V
DC Input Voltage:..................................–0.5V to VDD + 0.5V
Junction Temperature .................................–40°C to +140°C
Operating Temperature:...................................... 0°C to 70°C
Storage Temperature.................................. –65°C to +150°C
Static Discharge Voltage (ESD).......................... 2,000V-Min.
SSCG Theory of Operation
The SM560 is a PLL-type clock generator using a proprietary
Cypress design. By precisely controlling the bandwidth of the
output clock, the SM560 becomes a Low EMI clock generator.
The theory and detailed operation of the SM560 will be
discussed in the following sections.
EMI
All digital clocks generate unwanted energy in their harmonics.
Conventional digital clocks are square waves with a duty cycle
that is very close to 50%. Because of this 50/50-duty cycle,
digital clocks generate most of their harmonic energy in the
odd harmonics, i.e.; third, fifth, seventh, etc. It is possible to
reduce the amount of energy contained in the fundamental
and odd harmonics by increasing the bandwidth of the funda-
mental clock frequency. Conventional digital clocks have a
very high Q factor, which means that all of the energy at that
frequency is concentrated in a very narrow bandwidth, conse-
quently, higher energy peaks. Regulatory agencies test
electronic equipment by the amount of peak energy radiated
from the equipment. By reducing the peak energy at the funda-
mental and harmonic frequencies, the equipment under test is
able to satisfy agency requirements for EMI. Conventional
methods of reducing EMI have been to use shielding, filtering,
multi-layer PCBs, etc. The SM560 uses the approach of
reducing the peak energy in the clock by increasing the clock
bandwidth, and lowering the Q.
SSCG
SSCG uses a patented technology of modulating the clock
over a very narrow bandwidth and controlled rate of change,
both peak and cycle to cycle. The SM560 takes a narrow band
digital reference clock in the range of 25–108 MHz and
produces a clock that sweeps between a controlled start and
stop frequency and precise rate of change. To understand
what happens to a clock when SSCG is applied, consider a
65-MHz clock with a 50% duty cycle. From a 65-MHz clock we
know the following:
Note:
1.
Single Power Supply: The Voltage on any input or I/O pin cannot exceed the power pin during power up.
Table 2. DC Electrical Characteristics: VDD = 3.3V, Temp. = 25°C and CL (Pin 4) = 15 pF, unless otherwise noted
Parameter
Description
Conditions
Min.
Typ.
Max.
Unit
VDD
Power Supply Range
±10%
2.97
3.3
3.63
V
VINH
Input High Voltage
S0 and S1 only
0.85VDD
VDD
VDD
V
VINM
Input Middle Voltage
S0 and S1 only
0.40VDD
0.50VDD
0.60VDD
V
VINL
Input Low Voltage
S0 and S1 only
0.0
0.0
0.15VDD
V
VOH1
Output High Voltage
IOH = 6 mA
2.4
V
VOH2
Output High Voltage
IOH = 20 mA
2.0
V
VOL1
Output Low Voltage
IOH = 6 mA
0.4
V
VOL2
Output Low Voltage
IOH = 20 mA
1.2
V
Cin1
Input Capacitance
Xin/CLK (Pin 1)
3
4
5
pF
Cin2
Input Capacitance
Xout (Pin 8)
6
8
10
pF
Cin2
Input Capacitance
S0, S1, SSCC (Pins 7,6,5)
3
4
5
pF
IDD1
Power Supply Current
FIN = 40 MHz
30
40
mA
IDD2
Power Supply Current
FIN = 65 MHz
35
45
mA
Table 3. Electrical Timing Characteristics: VDD = 3.3V, T = 25°C and CL = 15 pF, unless otherwise noted
Parameter
Description
Conditions
Min.
Typ.
Max.
Unit
ICLKFR
Input Clock Frequency Range
VDD = 3.30V
25
108
MHz
Trise
Clock Rise Time (Pin 4)
SSCLK1 @ 0.4 – 2.4V
1.2
1.4
1.6
ns
Tfall
Clock Fall Time (Pin 4)
SSCLK1 @ 0.4 – 2.4V
1.2
1.4
1.6
ns
DTYin
Input Clock Duty Cycle
XIN/CLK (Pin 1)
20
50
80
%
DTYout
Output Clock Duty Cycle
SSCLK1 (Pin 4)
45
50
55
%
JCC
Cycle-to-Cycle Jitter
Fin = 25 – 108 MHz
-
125
175
ps


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