ChipFind - документация

Электронный компонент: W181-52G

Скачать:  PDF   ZIP
Peak Reducing EMI Solution
W181
Cypress Semiconductor Corporation
3901 North First Street
San Jose
CA 95134
408-943-2600
Document #: 38-07152 Rev. *A
Revised September 25, 2001
Features
Cypress PREMISTM
family offering
Generates an EMI optimized clocking signal at the out-
put
Selectable input to output frequency
Single 1.25% or 3.75% down or center spread output
Integrated loop filter components
Operates with a 3.3V or 5V supply
Low power CMOS design
Available in 8-pin SOIC (Small Outline Integrated Cir-
cuit) or 14-pin TSSOP (Thin Shrink Small Outline Pack-
age select options only)
Key Specifications
Supply Voltages: ...........................................V
DD
= 3.3V5%
or V
DD
= 5V10%
Frequency Range: ............................ 28 MHz
F
in
75 MHz
Crystal Reference Range.................. 28 MHz
F
in
40 MHz
Cycle to Cycle Jitter: ....................................... 300 ps (max.)
Selectable Spread Percentage: ....................1.25% or 3.75%
Output Duty Cycle: ............................... 40/60% (worst case)
Output Rise and Fall Time: .................................. 5 ns (max.)
Table 1. Modulation Width Selection
SS%
W181-01, 02, 03
Output
W181-51, 52, 53
Output
0
F
in
F
out
F
in
1.25%
F
in
+ 0.625%
F
in
0.625%
1
F
in
F
out
F
in
3.75%
F
in
+ 1.875%
F
in
1.875%
Table 2. Frequency Range Selection
W181 Option#
FS2
FS1
-01, 51
(MHz)
-02, 52
(MHz)
-03, 53
(MHz)
0
0
28
F
IN
38
28
F
IN
38
N/A
0
1
38
F
IN
48
38
F
IN
48
N/A
1
0
46
F
IN
60
N/A
46
F
IN
60
1
1
58
F
IN
75
N/A
58
F
IN
75
PREMIS is a trademark of Cypress Semiconductor Corporation.
Simplified Block Diagram
Pin Configurations
W
181-02/
03
8
7
6
5
1
2
3
4
CLKIN or X1
NC or X2
GND
SS%
SSON#
FS1
VDD
CLKOUT
W
181-01/
51
8
7
6
5
1
2
3
4
CLKIN or X1
NC or X2
GND
SS%
FS2
FS1
VDD
CLKOUT
SOIC
Spread Spectrum
W181
(EMI suppressed)
3.3 or 5.0V
Oscillator or
Spread Spectrum
W181
(EMI suppressed)
3.3 or 5.0V
XTAL
X1
X2
Reference Input
Input
Output
Output
40 MHz
Max.
W
181-01
8
1
2
3
4
CLKIN or X1
NC or X2
GND
SS%
NC
FS1
VDD
CLKOUT
5
6
7
9
10
11
12
13
14
FS2
NC
NC
NC
NC
NC
TSSOP
W
181-52/
53
W181
Document #: 38-07152 Rev. *A
Page 2 of 10
Pin Definitions
Pin Name
Pin No.
(SOIC)
Pin No.
(TSSOP)(-01)
Pin
Type
Pin Description
CLKOUT
5
8
O
Output Modulated Frequency: Frequency modulated copy
of the unmodulated input clock (SSON# asserted).
CLKIN or X1
1
2
I
Crystal Connection or External Reference Frequency In-
put:
This pin has dual functions. It may either be connected
to an external crystal, or to an external reference clock.
NC or X2
2
3
I
Crystal Connection: If using an external reference, this pin
must be left unconnected.
SSON#
8(02/03/52/
53)
--
I
Spread Spectrum Control (Active LOW): Asserting this sig-
nal (active LOW) turns the internal modulation waveform on.
This pin has an internal pull-down resistor.
FS1:2
7, 8 (01/51)
12, 1
I
Frequency Selection Bit(s) 1 and 2: These pins select the
frequency range of operation. Refer to Table 2. These pins
have internal pull-up resistors.
SS%
4
6
I
Modulation Width Selection: When Spread Spectrum fea-
ture is turned on, this pin is used to select the amount of
variation and peak EMI reduction that is desired on the output
signal. This pin has an internal pull-up resistor.
VDD
6
10
P
Power Connection: Connected to 3.3V or 5V power supply.
GND
3 4
G
Ground Connection: Connect all ground pins to the com-
mon system ground plane.
NC
5, 7, 9, 11, 13,
14
NC
No Connection.
W181
Document #: 38-07152 Rev. *A
Page 3 of 10
Overview
The W181 products are one series of devices in the Cypress
PREMIS family. The PREMIS family incorporates the latest
advances in PLL spread spectrum frequency synthesizer tech-
niques. By frequency modulating the output with a low-
frequency carrier, peak EMI is greatly reduced. Use of this
technology allows systems to pass increasingly difficult EMI
testing without resorting to costly shielding or redesign.
In a system, not only is EMI reduced in the various clock lines,
but also in all signals which are synchronized to the clock.
Therefore, the benefits of using this technology increase with
the number of address and data lines in the system. The Sim-
plified Block Diagram on page 1 shows a simple implementa-
tion.
Functional Description
The W181 uses a Phase-Locked Loop (PLL) to frequency
modulate an input clock. The result is an output clock whose
frequency is slowly swept over a narrow band near the input
signal. The basic circuit topology is shown in Figure 1. The
input reference signal is divided by Q and fed to the phase
detector. A signal from the VCO is divided by P and fed back
to the phase detector also. The PLL will force the frequency of
the VCO output signal to change until the divided output signal
and the divided reference signal match at the phase detector
input. The output frequency is then equal to the ratio of P/Q
times the reference frequency. (Note: For the W181 the output
frequency is equal to the input frequency.) The unique feature
of the Spread Spectrum Frequency Timing Generator is that a
modulating waveform is superimposed at the input to the VCO.
This causes the VCO output to be slowly swept across a pre-
determined frequency band.
Because the modulating frequency is typically 1000 times
slower than the fundamental clock, the spread spectrum pro-
cess has little impact on system performance.
Frequency Selection With SSFTG
In Spread Spectrum Frequency Timing Generation, EMI re-
duction depends on the shape, modulation percentage, and
frequency of the modulating waveform. While the shape and
frequency of the modulating waveform are fixed for a given
frequency, the modulation percentage may be varied.
Using frequency select bits (FS1:2 pins), the frequency range
can be set. Spreading percentage is set to be 1.25% or 3.75%
(see Table 1).
A larger spreading percentage improves EMI reduction. How-
ever, large spread percentages may either exceed system
maximum frequency ratings or lower the average frequency to
a point where performance is affected. For these reasons,
spreading percentages between 0.5% and 2.5% are most
common.
Freq.
Phase
Modulating
VCO
Post
CLKOUT
Detector
Charge
Pump
Waveform
Dividers
Divider
Feedback
Divider
PLL
GND
V
DD
Q
P
Clock Input
Reference Input
(EMI suppressed)
Figure 1. Functional Block Diagram
W181
Document #: 38-07152 Rev. *A
Page 4 of 10
Spread Spectrum Frequency Timing Genera-
tion
The device generates a clock that is frequency modulated in
order to increase the bandwidth that it occupies. By increasing
the bandwidth of the fundamental and its harmonics, the am-
plitudes of the radiated electromagnetic emissions are re-
duced. This effect is depicted in Figure 2.
As shown in Figure 2, a harmonic of a modulated clock has a
much lower amplitude than that of an unmodulated signal. The
reduction in amplitude is dependent on the harmonic number
and the frequency deviation or spread. The equation for the
reduction is:
dB = 6.5 + 9*log
10
(P) + 9*log
10
(F)
Where P is the percentage of deviation and F is the frequency
in MHz where the reduction is measured.
The output clock is modulated with a waveform depicted in
Figure 3. This waveform, as discussed in "Spread Spectrum
Clock Generation for the Reduction of Radiated Emissions" by
Bush, Fessler, and Hardin produces the maximum reduction
in the amplitude of radiated electromagnetic emissions. Figure
3
details the Cypress spreading pattern. Cypress does offer
options with more spread and greater EMI reduction. Contact
your local Sales representative for details on these devices.
SSFTG
Typical Clock
Frequency Span (MHz)
Amp
litu
d
e
(d
B)
Spread
Spectrum
Enabled
EMI Reduction
Spread
Spectrum
Non-
Frequency Span (MHz)
Down Spread
Am
p
lit
u
d
e
(
d
B)
Center Spread
Figure 2. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
MAX.
MIN.
10
%
20
%
30
%
40
%
50
%
60
%
70
%
80
%
90
%
10
0%
10
%
20
%
30
%
40
%
50
%
60
%
70
%
80
%
90
%
10
0%
F
R
EQUENCY
Figure 3. Typical Modulation Profile
W181
Document #: 38-07152 Rev. *A
Page 5 of 10
Absolute Maximum Ratings
[1]
Stresses greater than those listed in this table may cause per-
manent damage to the device. These represent a stress rating
only. Operation of the device at these or any other conditions
above those specified in the operating sections of this specifi-
cation is not implied. Maximum conditions for extended peri-
ods may affect reliability.
Parameter
Description
Rating
Unit
V
DD
, V
IN
Voltage on any pin with respect to GND
0.5 to +7.0
V
T
STG
Storage Temperature
65 to +150
C
T
A
Operating Temperature
0 to +70
C
T
B
Ambient Temperature under Bias
55 to +125
C
P
D
Power Dissipation
0.5
W
DC Electrical Characteristics
: 0C < T
A
< 70C, V
DD
= 3.3V 5%
Parameter
Description
Test Condition
Min.
Typ.
Max.
Unit
I
DD
Supply Current
18
32
mA
t
ON
Power-Up Time
First locked clock cycle after Power
Good
5
ms
V
IL
Input Low Voltage
0.8
V
V
IH
Input High Voltage
2.4
V
V
OL
Output Low Voltage
0.4
V
V
OH
Output High Voltage
2.4
V
I
IL
Input Low Current
Note 2
100
A
I
IH
Input High Current
Note 2
10
A
I
OL
Output Low Current
@ 0.4V, V
DD
= 3.3V
15
mA
I
OH
Output High Current
@ 2.4V, V
DD
= 3.3V
15
mA
C
I
Input Capacitance
All pins except CLKIN
7
pF
C
I
Input Capacitance
CLKIN pin only
6
10
pF
R
P
Input Pull-Up Resistor
500
k
Z
OUT
Clock Output Impedance
25
Note:
1.
Single Power Supply: The voltage on any input or I/O pin cannot exceed the power pin during power-up.
2.
Inputs FS1:2 have a pull-up resistor; Input SSON# has a pull-down resistor.